Modulation of the intestinal microbiota and morphology of tilapia, Oreochromis niloticus, following the application of a multi-species probiotic

Hematological changes in Florida pompano (Trachinotus carolinus) supplemented with β-glucan and Pediococcus acidilactici synbiotic

Florida pompano (Trachinotus carolinus) are a species of growing interest for commercial aquaculture. Effective health monitoring is crucial to the successful growout of the species, and prophylactic and therapeutic use of chemicals and antibiotics has been the traditional strategy for promoting stock health. However, concerns about antimicrobial resistance, chemical residues in seafood products and the environment, and resultant immunosuppression have prompted the industry to identify alternative management strategies, including supplementation with prebiotics, probiotics, and combinations of both (synbiotics). The objectives of this study are to determine and compare hematological, plasma biochemical, and plasma protein electrophoresis data of synbiotic-supplemented (β-glucan and Pediococcus acidilactici) and non-supplemented Florida pompano. Reference intervals for blood analytes are provided for both groups and for subgroups (females, males, large, and small fish) where statistically significant results exist. There are no differences between the hematological and plasma biochemistry analytes between the supplemented and control groups, except for blood urea nitrogen and carbon dioxide, indicating a possible effect of synbiotic supplementation on gill function and osmoregulation. Sex-related and size-related differences are observed within each of the control and supplemented groups; however, biometric measurements do not strongly correlate with blood analytes. These data represent baseline hematological and plasma biochemical data in the Florida pompano and indicate the safety of synbiotic supplementation in this commercially important species. This study serves to further the commercialization of Florida pompano by providing blood analyte reference intervals for health monitoring in the aquaculture setting.

A Novel Postbiotic Product Based on Weissella cibaria for Enhancing Disease Resistance in Rainbow Trout: Aquaculture Application

Postbiotics are innovative tools in animal husbandry, providing eco-friendly solutions for disease management within the industry. In this study, a new postbiotic product was evaluated for its impact on the health of rainbow trout (Oncorhynchus mykiss). In vivo studies were conducted to assess the safety of the Weissella cibaria strains used in postbiotic production. Additionally, this study evaluated the impact of diet supplementation with 0.50% postbiotics on growth performance during a 30-day feeding trial; the gut microbial communities, immunomodulation, and protection against Yersinia ruckeri infection were evaluated. The strains did not harm the animals during the 20-day observation period. Furthermore, the effect of postbiotics on growth performance was not significant (p < 0.05). The treated group showed a significant increase in acid-lactic bacteria on the 30th day of the feeding trial, with counts of 3.42 ± 0.21 log CFU/mL. Additionally, there was an up-regulation of the pro-inflammatory cytokine IL-1β in head kidney samples after 48 h of feed supplementation, whereas cytokines IL-10, IL-8, INF-γ, and TNF-α were down-regulated. The findings indicate that rainbow trout fed with postbiotics saw an improvement in their survival rate against Y. ruckeri, with a 20.66% survival improvement in the treated group. This study proves that incorporating postbiotics from two strains of W. cibaria previously isolated from rainbow trout into the diet of fish has immunomodulatory effects, enhances intestinal microbial composition, and improves fish resistance against Y. ruckeri.

Dietary Protein Quality Affects the Interplay between Gut Microbiota and Host Performance in Nile Tilapia

Dietary protein quality plays a key role in maintaining intestinal mucosal integrity, but also modulates the growth of luminal microorganisms. This work assessed the effect of dietary protein sources on the performance, gut morphology, and microbiome in Nile tilapia. Four isonitrogenous and isolipidic diets comprising equivalent amounts of the protein supply derived from either PLANT, ANIMAL, INSECT, or BACTERIAL (bacterial biomass) sources were fed to triplicate groups of fish (IBW: 12 g) for 46 days. Fish fed the ANIMAL and BACTERIAL diets showed significantly higher weight gains than those fed the PLANT and INSECT diets (p < 0.05). Relative abundance at the phylum level showed that Bacteroidetes, Fusobacteria, and Proteobacteria were the more abundant phyla in tilapia's intestine, while Cetobacterium was the most representative genus in all treatments. Interesting patterns were observed in the correlation between amino acid intake and genus and species abundance. Metabolism prediction analysis showed that BACTERIAL amine and polyamine degradation pathways are modulated depending on diets. In conclusion, different protein sources modulate the relationship between bacteria functional pathways and amino acid intake.

Microbiota plasticity in tilapia gut revealed by meta-analysis evaluating the effect of probiotics, prebiotics, and biofloc

Tilapia species are among the most cultivated fish worldwide due to their biological advantages but face several challenges, including environmental impact and disease outbreaks. Feed additives, such as probiotics, prebiotics, and other microorganisms, have emerged as strategies to protect against pathogens and promote immune system activation and other host responses, with consequent reductions in antibiotic use. Because these additives also influence tilapia's gut microbiota and positively affect the tilapia culture, we assume it is a flexible annex organ capable of being subject to significant modifications without affecting the biological performance of the host. Therefore, we evaluated the effect of probiotics and other additives ingested by tilapia on its gut microbiota through a meta-analysis of several bioprojects studying the tilapia gut microbiota exposed to feed additives (probiotic, prebiotic, biofloc). A total of 221 tilapia gut microbiota samples from 14 bioprojects were evaluated. Alpha and beta diversity metrics showed no differentiation patterns in relation to the control group, either comparing additives as a group or individually. Results also revealed a control group with a wide dispersion pattern even when these fish did not receive additives. After concatenating the information, the tilapia gut core microbiota was represented by four enriched phyla including Proteobacteria (31%), Fusobacteria (23%), Actinobacteria (19%), and Firmicutes (16%), and seven minor phyla Planctomycetes (1%), Chlamydiae (1%), Chloroflexi (1%), Cyanobacteria (1%), Spirochaetes (1%), Deinococcus Thermus (1%), and Verrucomicrobia (1%). Finally, results suggest that the tilapia gut microbiota is a dynamic microbial community that can plastically respond to feed additives exposure with the potential to influence its taxonomic profile allowing a considerable optimal range of variation, probably guaranteeing its physiological function under different circumstances.

Histomorphological Changes in Fish Gut in Response to Prebiotics and Probiotics Treatment to Improve Their Health Status: A Review

The gastrointestinal tract (GIT) promotes the digestion and absorption of feeds, in addition to the excretion of waste products of digestion. In fish, the GIT is divided into four regions, the headgut, foregut, midgut, and hindgut, to which glands and lymphoid tissues are associated to release digestive enzymes and molecules involved in the immune response and control of host-pathogens. The GIT is inhabited by different species of resident microorganisms, the microbiota, which have co-evolved with the host in a symbiotic relationship and are responsible for metabolic benefits and counteracting pathogen infection. There is a strict connection between a fish's gut microbiota and its health status. This review focuses on the modulation of fish microbiota by feed additives based on prebiotics and probiotics as a feasible strategy to improve fish health status and gut efficiency, mitigate emerging diseases, and maximize rearing and growth performance. Furthermore, the use of histological assays as a valid tool for fish welfare assessment is also discussed, and insights on nutrient absorptive capacity and responsiveness to pathogens in fish by gut morphological endpoints are provided. Overall, the literature reviewed emphasizes the complex interactions between microorganisms and host fish, shedding light on the beneficial use of prebiotics and probiotics in the aquaculture sector, with the potential to provide directions for future research.

Evaluation of dietary single probiotic isolates and probiotic multistrain consortia in growth performance, gut histology, gut microbiota, immune regulation, and infection resistance of Nile tilapia, Oreochromis niloticus, shows superior monostrain performance

The probiotic potential of a designed bacterial consortia isolated from a competitive exclusion culture originally obtained from the intestinal contents of tilapia juveniles were evaluated on Nile tilapia alevins. The growth performance, intestinal histology, microbiota effects, resistance to Streptococcus agalactiae challenge, and immune response were assessed. In addition, the following treatments were included in a commercial feed: A12+M4+M10 (Lactococcus lactis A12, Priestia megaterium M4, and Priestia sp. M10), M4+M10 (P. megaterium M4, and Priestia sp. M10) and the single bacteria as controls; A12 (L. lactis A12), M4 (P. megaterium M4), M10 (Priestia sp. M10), also a commercial feed without any probiotic addition was included as a control. The results showed that all probiotic treatments improved the growth performance, intestinal histology, and resistance during experimental infection with S. agalactiae in comparison to the control fish. Also, the administration of probiotics resulted in the modulation of genes associated with the innate and adaptive immune systems that were non-dependent on microbial colonization. Surprisingly, L. lactis A12 alone induced benefits in fish compared to the microbial consortia, showing the highest increase in growth rate, survival during experimental infection with S. agalactiae, increased intestinal fold length, and the number of differentially expressed genes. Lastly, we conclude that a competitive exclusion culture is a reliable source of probiotics, and monostrain L. lactis A12 has comparable or even greater probiotic potential than the bacterial consortia.

Effect of eco-friendly probiotics-supplemented rapeseed meal-based diet on the performance of Catla catla fingerlings

Ever-increasing human population compels the researchers to search for alternative food sources such as fish meat. For increase of fish growth and proper feed utilization, probiotics were added in rapeseed meal-based diet in current trial for proper digestion and absorption of nutrients in fish and ultimately higher growth with lower aquatic pollution. Fish gut microbiota is important for the feed utilization and absorption in body for higher growth. A 70-day study was conducted to investigate the effects of probiotics-supplemented rapeseed meal-based diet on growth performance, digestibility of nutrients, and absorption of minerals in Catla catla fingerlings with lowering water pollution level. Six test diets were prepared by using different levels of multi-strain probiotics i.e. 0, 1, 2, 3, 4 and 5 g/kg (0.0-0.5%) in rapeseed meal-based diet. At the rate of 4% of live wet weight, Catla fingerlings were fed two times a day and faeces samples from each tank were collected. According to the results, it was observed that probiotics supplementation (@2 g/kg) in rapeseed meal-based diet resulted with improvement in nutrient digestibility (CP, 72%; fat, 75% and GE, 70%), mineral absorption (Ca, 72%; Na, 76%; K, 70% and P, 70%), specific growth rate (SGR, 1.55), improved feed conversion ratio (FCR, 1.22) and weight gain percentage (WG%, 303%) of fingerlings. It was also noticed that probiotics supplementation decreased the discharge of minerals and nutrient through faeces, as compared to control diet; hence, it plays a significant role in reducing water pollution. On the basis of these results, it was concluded that probiotics inclusion at level of 2 g/kg was useful to formulate the cost effective and eco-friendly fish feed with the maximum improvement in growth and fish health by using rapeseed meal-based diet, as compared to control and other test diets.

Effects of probiotics on growth, survival, and intestinal and liver morphometry of Gangetic mystus (Mystus cavasius)

The usage of probiotics proved advantageous in aquaculture due to its positive impact on fish growth, immune response and environment. This study was aimed to assess the effects of probiotics on growth, survival and histometry of intestine and liver in Gangetic mystus (Mystus cavasius) using two separate experiments for a period of 8 weeks (in aquaria) and 16 weeks (in earthen ponds). Three different probiotic treatments were incorporated i.e. commercial probiotic one; CP-1 (T1), commercial probiotic two; CP-2 (T2), Lab developed (Lab dev.) probiotic (T3) including a control. The results indicated that the probiotics usage especially Lab dev. probiotic (T3) significantly improved the growth parameters such as weight gain (g) and specific growth rate (SGR, %/day) as well as ensured better feed conversion efficiency. Zero mortality was observed in aquaria whereas probiotic application enhanced survivability in earthen ponds. Moreover, all probiotic treatment exhibited positive results for different histo-morphometric features of intestine and liver. Mucus secreting goblet cells and fattening of mucosal fold increased significantly with probiotic usage. The amount of regular shaped nucleus was maximum in T3 with least intra cellular distance between liver tissues in earthen ponds. The greatest value for hemoglobin with lowest glucose level was observed in T3 as well. Furthermore, probiotic ensured low concentration of ammonia during culture. Overall, it was anticipated that the application of probiotics in Gangetic mystus culture resulted positive effect on its growth, feed utilization, survivability, histo-morphometry, immunity and hematological parameters.

A comparative study on effects of dietary three strains of lactic acid bacteria on the growth performance, immune responses, disease resistance and intestinal microbiota of Pacific white shrimp, Penaeus vannamei

The present study evaluated the growth performance, immune responses, disease resistance and intestinal microbiota in Penaeus vannamei fed diets supplemented with three strains of lactic acid bacteria (LAB). The basal diet (control, CO) supplemented with Lactobacillus plantarum W2 (LA), Pediococcus acidilactici Nj (PE), Enterococcus faecium LYB (EN) and florfenicol (FL), respectively, formed three LAB diets (1 × 10¹⁰ cfu kg^-1) and a florfenicol diet (15 mg kg^-1, positive control), were fed to shrimp for 42 days. Results indicated that specific growth rate, feed efficiency rate, and disease resistance of shrimp against Vibrio parahaemolyticus in the treatment groups were significantly improved versus the control (P < 0.05). Compared with the control, acid phosphatase, alkaline phosphatase, phenonoloxidase, total nitric oxide synthase, peroxidase, superoxide dismutase activities, total antioxidant capacity, and lysozyme content in the serum and the relative expression levels of SOD, LZM, proPO, LGBP, HSP70, Imd, Toll, Relish, TOR, 4E-BP, eIF4E1α and eIF4E2 genes in the hepatopancreas of LAB groups were enhanced to various extents. Intestinal microbiota analysis showed that the LA and EN groups significantly improved microbial diversity and richness, and LAB groups significantly altered intestinal microbial structure of shrimp. At the phylum level, the Verrucomicrobiota in the LA and PE groups, the Firmicutes in the EN group, and the Actinobacteriota in the PE and EN groups were enriched. Moreover, the CO group increased the proportion of potential pathogens (Vibrionaceae and Flavobacteriaceae). The potential pathogen (Vibrio) was reduced, and potential beneficial bacteria (Tenacibaculum, Ruegeria and Bdellovibrio) were enriched in response to dietary three strains of LAB. When the intestinal microbiota homeostasis of shrimp is considered, L. plantarum and E. faecium showed better effects than P. acidilactici. However, due to the concerns on the possible potential risks of E. faecium strains to human health, L. plantarum W2 is more suitable for application in aquaculture than E. faecium LYB. Considering collectively the above, Lactobacillus plantarum W2 could be applied as better probiotic to improve the growth performance, non-specific immunity, disease resistance and promote intestinal health of P. vannamei.

Effects of two host-associated probiotics Bacillus mojavensis B191 and Bacillus subtilis MRS11 on growth performance, intestinal morphology, expression of immune-related genes and disease resistance of Nile tilapia (Oreochromis niloticus) against Streptococcusiniae

The intensification and diversification of production systems have increased the incidence of diseases, which are usually treated with antibiotics. However, its use should be restricted due to the increasing prevalence of antibiotic-resistant bacteria. Probiotics represent therefore an alternative environmentally friendly strategy for improving growth and disease resistance in aquaculture. Considering that host-derived probiotics may offer greater advantages than those from other environments in terms of safety and efficacy, two potential host-associated probiotic strains (Bacillus mojavensis B191 and Bacillus subtilis MRS11) were used in the present study, which were previously isolated from intestinal mucus of Nile tilapia (Oreochromis niloticus). This study was conducted to assess the effects of dietary administration of two Bacillus strains on growth performance, intestinal morphology, immunity, and disease resistance of Nile tilapia. A total of 375 fish were randomly divided into five groups in triplicate. Nile tilapia were fed a basal diet (control group) or a basal diet supplemented with Bacillus mojavensis B191 (BM) or Bacillus subtilis MRS11 (BS) spores at different concentrations of 1 × 10⁶ (BM6 and BS6, respectively) and 1 × 10⁸ (BM8 and BS8, respectively) CFU/g of feed for 60 days. Moreover, the survival rate of tilapia upon challenge with Streptococcus iniae was determined following the feeding trial. After the feeding trial, the growth performances were significantly improved in all probiotic-fed groups, with the BS8 group being the highest. Light and electron microscopy observations revealed elevated goblet cells, intestinal villus length (except BM8), microvilli length, microvilli density, and perimeter ratio increase in the intestine of all probiotic-fed groups compared with the control group. Regarding the expression analysis, HSP70 gene was only up-regulated in the BM8 group and a general trend of up-regulation of some immune-related cytokines (TGF-β, IL-10, TNF-α and IL-1β) was observed in all probiotic-fed groups. Likewise, the best protection against Streptococcus iniae was observed in the BS8 group, followed by BS6, BM6 and BM8 groups. Altogether, dietary probiotic supplementation with BS8 and BM6 may improve growth performance, intestinal morphology, immunity, and disease resistance in Nile tilapia.

Dietary Supplementation of a Commercial Prebiotic, Probiotic and Their Combination Affected Growth Performance and Transient Intestinal Microbiota of Red Drum (Sciaenops ocellatus L.)

In the present study, the potential synergism between beneficial lactic acid bacteria (Pediococcus acidilactici) contained in a probiotic and a mixture of fermentable complex carbohydrates and autolyzed brewer's yeast (or prebiotic) were explored in red drum. Four experimental diets were formulated from practical ingredients, and the basal diet was supplemented with either probiotic, prebiotic, or both supplements. Red drum juveniles (~5.5 g) were offered the four experimental diets for 56 days, and at the end of the feeding trial fish fed diets supplemented with probiotic had significantly better weight gain than those fed the non-supplemented diets, and higher protein content in their whole-body composition. Transient intestinal microbiome alpha and beta diversity were significantly affected by the dietary treatments. Interestingly, a higher relative abundance of the lactic acid genus Pediococcus was observed for fish fed diets supplemented with the prebiotic. A higher relative abundance was also observed for the predicted functions of the microbial metagenome, and many of these pathways involved the biosynthesis of essential amino acids, vitamins, and nucleotides. Even though no potential synergistic effect was observed, the individual inclusion of these prebiotic and probiotic supplements positively affected the intestinal health and growth performance of red drum, respectively.

Synbiotic Lactic Dry® enhanced the growth performance, growth-related genes, intestinal health, and immunity of Nile tilapia reared in inland brackish groundwater

Nile tilapia is recognized as a suitable candidate for intensive farming and sustainability of the aquaculture industry. However, one issue limiting Nile tilapia expansion in arid and semi-arid areas is the scarcity of freshwater resources. In this study, the supplementation of synbiotics was investigated to enhance the growth performance, growth-related genes, intestinal health, and immunity of Nile tilapia reared in inland brackish groundwater. Four diets were prepared where the basal diets were mixed with the dietary mixture of probiotics and prebiotics (Synbiotic Lactic Dry®, a blend of Saccharomyces cerevisiae, Lactobacillus acidophilus, Streptococcus faecium, and Bacillus subtilis, mannan oligosaccharides and β-1.3/1.6-D-glucan) at 0, 0.5, 1, and 2 g/kg. After eight weeks, the final weight and weight gain are linearly increasing with increasing the supplementation level of synbiotic. Markedly fish fed 0.5, 1, and 2 g/kg of synbiotic had higher final weight, weight gain, and feed intake and lower feed conversion ratio (FCR) than fish fed synbiotic free diet. The specific growth rate (SGR) was significantly higher in fish fed 1 and 2 g/kg than in fish fed 0 and 0.5 g/kg. The intestine of fish fed on synbiotic shows an increase in intestinal villi density. Further, the intestine of fish fed on synbiotic showed an increase in the length and branching intestinal villi (anterior, middle, and posterior) in a dose-dependent manner. The lysozyme and phagocytic activities were significantly different from the control, while synbiotic supplementation did not affect the phagocytic index. Interestingly, the results showed marked upregulation of ghrelin, IGF-1, and GH genes in fish fed synbiotics at 0.5, 1, and 2 g/kg. In addition, fish fed 2 g/kg had the highest expression of ghrelin, IGF-1, and GH genes. In conclusion, growing Nile tilapia in inland brackish groundwater can be achieved without negative impacts on the growth performance and health status. Supplementing synbiotics (1-2 g/kg) in Nile tilapia feeds enhanced the growth and feed performances, intestinal histomorphological features, growth-related genes, and immune response.

Rice protein concentrate as a fish meal substitute in Oreochromis niloticus: Effects on immune response, intestinal cytokines, Aeromonas veronii resistance, and gut microbiota composition

The potential of rice protein concentrate (RPC) to substitute fishmeal (FM) protein in the diet of Oreochromis niloticus was assessed in a five-month-long feeding trial. Fishmeal protein was replaced by RPC at rates of 0% (control), 25%, 50%, and 75% (RPC0, RPC25, RPC50, and RPC75, respectively). RPC25 had no significant effect on antioxidant capacity (total antioxidant capacity; superoxide dismutase, catalase, and glutathione peroxidase activities) and immune indices (lysozyme, nitric oxide, antiprotease, and bactericidal activities) after one, two, and five months of feeding, while the values for these parameters were significantly lower in the RPC75 group compared to those in the RPC0 group. The RPC25 group showed higher mRNA levels of the intestinal cytokines IL-1β, IL-10β, TGF-β, and TNF-α than the control group. In fish affected by Aeromonas veronii, the highest significant cumulative mortality was recorded in the RPC75 group, followed by the RPC50, RPC25, and control groups. Gut microbiome analyses showed a reduction in microbial diversity in response to the addition of RPC, regardless of the RPC content, and the composition of the community of the RPC samples differed from that of the control. RPC-enriched diets resulted in higher relative abundances of Bacteroidetes and Fusobacteria in the gut compared to that in the gut of the control fish. In summary, RPC can be used to replace up to 25% of the FM protein in the diet of O. niloticus, while improving the antioxidant capacity, immunocompetence, and disease resistance of the fish.

Effective Regulation of Gut Microbiota With Probiotics and Prebiotics May Prevent or Alleviate COVID-19 Through the Gut-Lung Axis

Coronavirus disease 2019 (COVID-19) can disrupt the gut microbiota balance, and patients usually have intestinal disorders. The intestine is the largest immune organ of the human body, and gut microbes can affect the immune function of the lungs through the gut-lung axis. Many lines of evidence support the role of beneficial bacteria in enhancing human immunity, preventing pathogen colonization, and thereby reducing the incidence and severity of infection. In this article, we review the possible approach of modulating microbiota to help prevent and treat respiratory tract infections, including COVID-19, and discuss the possibility of using probiotics and prebiotics for this purpose. We also discuss the mechanism by which intestinal micro-flora regulate immunity and the effects of probiotics on the intestinal micro-ecological balance. Based on this understanding, we propose the use of probiotics and prebiotics to modulate gut microbiota for the prevention or alleviation of COVID-19 through the gut-lung axis.

Effect of Enterococcus faecium as a Water and/or Feed Additive on the Gut Microbiota, Hematologic and Immunological Parameters, and Resistance Against Francisellosis and Streptococcosis in Nile Tilapia (Oreochromis niloticus)

In the present study, we evaluated the effects of administering Enterococcus faecium in food and/or water on the hematological and immunological parameters, intestinal microbiota, resistance to bacterial diseases (streptococcosis and francisellosis) and growth of Nile tilapia. Before the in vivo experiment, probiotic bacteria isolated from Nile tilapia were selected via inhibition tests. Sequencing, annotation, and assembly of the complete genome of the selected bacteria as well as other tests were performed using bioinformatics tools. Three treatments were implemented: G1 (probiotic feeding), G2 (probiotic in water), and G3 (probiotic in food and water); and a negative control (NC) was also employed. Treatment lasted 38 days, and each group consisted of fish and two repetitions. The fish were divided and infected with Streptococcus agalactiae S13 (serotype Ib) and Francisella orientalis. The G1 group had a higher average final weight gain than the G2, G3, and NC groups. Further, a significant increase in the number of thrombocytes was observed in the groups administered probiotics in the diet (G1 and G3). A statistical difference was observed in the mortality of fish infected with S. agalactiae in the NC compared to the treated groups. Cetobacterium was the 43 most abundant genus in the intestinal microbiota of all groups, including the NC group. E. faecium increased the immunity of fish administered the treatment and decreased the mortality caused by S. agalactiae. As an autochtone probiotic, E. faecium does not interfere with the local ecosystem and thus has a great probiotic potential for Nile tilapia in Brazil.

The functionality of probiotics in aquaculture: An overview

Probiotics are live beneficial bacteria introduced into the gastrointestinal tract through food or water, promoting good health by enhancing the internal microbial balance. Probiotic microbes produce bacteriocins, siderophores, lysozymes, proteases, and hydrogen peroxides, inhibiting the growth of harmful pathogens. Such beneficial bacteria also produce many enzymes such as amylase enzyme by Aeromonas spp., Bacillus subtilis, Bacteridaceae, Clostridium spp., Lactobacillus plantarum, and Staphylococcus sp., and protease and cellulase enzymes by B. subtilis, L. plantarum, and Staphylococcus sp. In aquaculture, probiotics confer several benefits and play important roles in improving growth performances, disease resistance, immunity, health status, intestinal epithelial barrier integrity, gut microbiome, and water quality. In addition, the practical application of probiotics in aquaculture diets could minimize antibiotic side effects. Promoting these feed additives for fish would help to improve their productive performance and feed utilization and, therefore, boost fish production and safeguard human health. This review provides updated information regarding definitions, sources of bacterial probiotics, probiotic use in fish diets against pathogenic bacteria, mechanisms of action, beneficial aspects, and potential applications of probiotics in fish. It is anticipated that these will be of significant value for nutritionists, agricultural engineers, researchers, pharmacists, scientists, pharmaceutical industries, and veterinarians.

The Efficacy of Moina micrura Enriched with Probiotic Bacillus pocheonensis in Enhancing Survival and Disease Resistance of Red Hybrid Tilapia (Oreochromis spp.) Larvae

The administration of probiotics via live feeds, such as Artemia and rotifers, has gained significant attention. Moreover, indiscriminate use of antibiotics in conventional aquaculture practices in order to prevent or control disease outbreaks has resulted in the occurrence of residues and antimicrobial resistance. Thus, the application of eco-friendly feed additives, such as probiotics, as a safer alternative has received increasing attention in recent years. However, only minimal information on the administration of probiotics via freshwater cladoceran Moina micrura is available despite being commonly used for larval and post-larval feeding of freshwater crustaceans and fish. Thus, this study aimed to evaluate the application of Bacillus pocheonensis strain S2 administered via M. micrura to red hybrid tilapia (Oreochromis spp.) larvae. Bacillus pocheonensis that has been previously isolated from Spirulina sp. was subjected to preliminary in vitro evaluation of antagonistic properties. The agar well-diffusion assay revealed that this probiont could inhibit the growth of Streptococcus agalactiae and Aeromonas hydrophila. The size of inhibition zones ranged from 8.8 ± 0.2 to 18.2 ± 0.4 mm. Moina micrura was later used as a biological model in preliminary in vivo bacterial challenge assays to evaluate the efficacy of B. pocheonensis in protecting the host from diseases. Moina micrura was pre-enriched with B. pocheonensis at 104 and 106&nbsp;CFU&nbsp;mL-1 before S. agalactiae and A. hydrophila were introduced into the culture. The study revealed that B. pocheonensis at 104&nbsp;CFU&nbsp;mL-1 was able to significantly enhance the survival of M. micrura after being challenged with both pathogens (63 ± 3%) in comparison to the control group. The relative percentage survival (RPS) of M. micrura was highest (p < 0.05) when treated with B. pocheonensis at both concentrations 104 and 106&nbsp;CFU&nbsp;mL-1 (38.33) after being challenged against S. agalactiae. To assess the efficacy of B. pocheonensis in protecting red hybrid tilapia against streptococcosis, the larvae were fed with either unenriched (control) Moina or probiont-enriched Moina daily for 10 days. A significantly (p < 0.05) higher survival rate (77 ± 3%) was observed in larvae fed with probiont-enriched M. micrura compared to other treatments, and the RPS was recorded at 62.90. In addition, the S. agalactiae load was suppressed in larvae fed probiont-enriched M. micrura (6.84±0.39&nbsp;CFU&nbsp;mL-1) in comparison to the control group (7.78±0.09&nbsp;CFU&nbsp;mL-1), indicating that the probiont might have contributed to the improvement of tilapia health and survival. This study illustrated that M. micrura was suitable to be used as a vector for probiotics in freshwater fish larvae as an alternative to hazardous antibiotics for disease control.

Aquaculture industry prospective from gut microbiome of fish and shellfish: An overview

The microbiome actually deals with micro-organisms that are associated with indigenous body parts and the entire gut system in all animals, including human beings. These microbes are linked with roles involving hereditary traits, defence against diseases and strengthening overall immunity, which determines the health status of an organism. Considerable efforts have been made to find out the microbiome diversity and their taxonomic identification in finfish and shellfish and its importance has been correlated with various physiological functions and activities. In recent past due to the availability of advanced molecular tools, some efforts have also been made on DNA sequencing of these microbes to understand the environmental impact and other stress factors on their genomic structural profile. There are reports on the use of next-generation sequencing (NGS) technology, including amplicon and shot-gun approaches, and associated bioinformatics tools to count and classify commensal microbiome at the species level. The microbiome present in the whole body, particularly in the gut systems of finfish and shellfish, not only contributes to digestion but also has an impact on nutrition, growth, reproduction, immune system and vulnerability of the host fish to diseases. Therefore, the study of such microbial communities is highly relevant for the development of new and innovative bio-products which will be a vital source to build bio and pharmaceutical industries, including aquaculture. In recent years, attempts have been made to discover the chemical ingredients present in these microbes in the form of biomolecules/bioactive compounds with their functions and usefulness for various health benefits, particularly for the treatment of different types of disorders in animals. Therefore, it has been speculated that microbiomes hold great promise not only as a cure for ailments but also as a preventive measure for the number of infectious diseases. This kind of exploration of new breeds of microbes with their miraculous ingredients will definitely help to accelerate the development of the drugs, pharmaceutical and other biological related industries. Probiotic research and bioinformatics skills will further escalate these opportunities in the sector. In the present review, efforts have been made to collect comprehensive information on the finfish and shellfish microbiome, their diversity and functional properties, relationship with diseases, health status, data on species-specific metagenomics, probiotic research and bioinformatics skills. Further, emphasis has also been made to carry out microbiome research on priority basis not only to keep healthy environment of the fish farming sector but also for the sustainable growth of biological related industries, including aquaculture.

Probiotic Bacteria with High Alpha-Gal Content Protect Zebrafish against Mycobacteriosis

Mycobacteriosis affects wild fish and aquaculture worldwide, and alternatives to antibiotics are needed for an effective and environmentally sound control of infectious diseases. Probiotics have shown beneficial effects on fish growth, nutrient metabolism, immune responses, disease prevention and control, and gut microbiota with higher water quality. However, the identification and characterization of the molecules and mechanisms associated with probiotics is a challenge that requires investigation. To address this challenge, herein we used the zebrafish model for the study of the efficacy and mechanisms of probiotic interventions against tuberculosis. First, bacteria from fish gut microbiota were identified with high content of the surface glycotope Galα1-3Galβ1-(3)4GlcNAc-R (α-Gal) that has been shown to induce protective immune responses. The results showed that probiotics of selected bacteria with high α-Gal content, namely Aeromonas veronii and Pseudomonas entomophila, were biosafe and effective for the control of Mycobacterium marinum. Protective mechanisms regulating immunity and metabolism activated in response to α-Gal and probiotics with high α-Gal content included modification of gut microbiota composition, B-cell maturation, anti-α-Gal antibodies-mediated control of mycobacteria, induced innate immune responses, beneficial effects on nutrient metabolism and reduced oxidative stress. These results support the potential of probiotics with high -Gal content for the control of fish mycobacteriosis and suggested the possibility of exploring the development of combined probiotic treatments alone and in combination with -Gal for the control of infectious diseases.

Gut microbiota of homologous Chinese soft-shell turtles (Pelodiscus sinensis) in different habitats

Background

Chinese soft-shell turtle (Pelodiscus sinensis) is an important commercial species for their high nutritional value and unique taste, but it has been a vulnerable species due to habitat loss. In this study, homologous juvenile turtles were allocated to lake, pond and paddy field to investigate the habitat effects on turtles.

Results

The growth, morphology and gut microbial communities were monitored during the 4 months cultural period. It showed higher growth rate of turtles in paddy field and pond. The appearance, visceral coefficients, gut morphology and microbial communities in turtles were distinct among different habitats. The microbial community richness on Chao1 was obviously lower in initial turtle guts from greenhouses, whereas it was relative higher in turtle guts sampled from paddy fields than ponds and lake. Significant differences on dominant microbes were found among initial and subsequent samples from different habitats. Firmicutes was the most abundant phylum in the guts of turtles sampled from the greenhouse initially, while Proteobacteria was the most abundant phylum after cultivation in different habitats, followed by Bacteroidetes. The microbial composition were distinct in different habitats at 60d, and the appearance of dominant phyla and genera was more driven by sampling time than habitats at 120d. Both the sampling time and habitats affected the appearance of dominant phyla and genera during the cultivation. The functional predictions indicated that both habitat type and sampling time had significant effects on metabolic pathways, especially amino acid and carbohydrate metabolism.

Conclusions

The turtles could adapt to natural lakes, artificial ponds and paddy fields. The gut microbial abundance was different among the habitats and sampling time. The species of microbes were significantly more diverse in paddy field specimens than in those from ponds and lakes. Rice-turtle coculture is a potential ecological and economic farming mode that plays important roles in wild turtle protection and food security.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12866-021-02209-y.

Multi-Strain Probiotics: Synergy among Isolates Enhances Biological Activities

The use of probiotics for health benefits is becoming popular because of the quest for safer products with protective and therapeutic effects against diseases and infectious agents. The emergence and spread of antimicrobial resistance among pathogens had prompted restrictions over the non-therapeutic use of antibiotics for prophylaxis and growth promotion, especially in animal husbandry. While single-strain probiotics are beneficial to health, multi-strain probiotics might be more helpful because of synergy and additive effects among the individual isolates. This article documents the mechanisms by which multi-strain probiotics exert their effects in managing infectious and non-infectious diseases, inhibiting antibiotic-resistant pathogens and health improvement. The administration of multi-strain probiotics was revealed to effectively alleviate bowel tract conditions, such as irritable bowel syndrome, inhibition of pathogens and modulation of the immune system and gut microbiota. Finally, while most of the current research focuses on comparing the effects of multi-strain and single-strain probiotics, there is a dearth of information on the molecular mechanisms of synergy among multi-strain probiotics isolates. This forms a basis for future research in the development of multi-strain probiotics for enhanced health benefits.

A Tentative Study of the Effects of Heat-Inactivation of the Probiotic Strain Shewanella putrefaciens Ppd11 on Senegalese Sole (Solea senegalensis) Intestinal Microbiota and Immune Response

Concerns about safety, applicability and functionality associated with live probiotic cells have led to consideration of the use of non-viable microorganisms, known as paraprobiotics. The present study evaluated the effects of dietary administration of heat-inactivated cells of the probiotic strain Shewanella putrefaciens Ppd11 on the intestinal microbiota and immune gene transcription in Solea senegalensis. Results obtained were evaluated and compared to those described after feeding with viable Pdp11 cells. S. senegalensis specimens were fed with basal (control) diet or supplemented with live or heat inactivated (60 °C, 1 h) probiotics diets for 45 days. Growth improvement was observed in the group receiving live probiotics compared to the control group, but not after feeding with a probiotic heat-inactivated diet. Regarding immune gene transcription, no changes were observed for tnfα, il-6, lys-c1, c7, hsp70, and hsp90aa in the intestinal samples based on the diet. On the contrary, hsp90ab, gp96, cd4, cd8, il-1β, and c3 transcription were modulated after probiotic supplementation, though no differences between viable and heat-inactivated probiotic supplemented diets were observed. Modulation of intestinal microbiota showed remarkable differences based on the viability of the probiotics. Thus, higher diversity in fish fed with live probiotic cells, jointly with increased Mycoplasmataceae and Spirochaetaceae to the detriment of Brevinemataceae, was detected. However, microbiota of fish receiving heat-inactivated probiotic cells showed decreased Mycoplasmataceae and increased Brevinemataceae and Vibrio genus abundance. In short, the results obtained indicate that the viable state of Pdp11 probiotic cells affects growth performance and modulation of S. senegalensis intestinal microbiota. On the contrary, minor changes were detected in the intestinal immune response, being similar for fish receiving both, viable and inactivated probiotic cell supplemented diets, when compared to the control diet.

Dietary Supplementation of Bacillus sp. SJ-10 and Lactobacillus plantarum KCCM 11322 Combinations Enhance Growth and Cellular and Humoral Immunity in Olive Flounder (Paralichthys olivaceus)

Experiments were conducted to identify different ratios of Bacillus sp. SJ-10 and Lactobacillus plantarum KCCM 11322 mixtures at a concentration of 1 × 10⁸ CFU/g diet; the effects on growth and cellular and humoral immune responses and the characteristics of disease protection in olive flounder (Paralichthys olivaceus). Flounder were divided into six groups and fed control diet D-1 (without Bacillus sp. SJ-10 and L. plantarum KCCM 11322), positive control diets D-2 (Bacillus sp. SJ-10 at 1 × 10⁸ CFU/g feed) and D-3 (L. plantarum KCCM 11322 at 1 × 10⁸ CFU/g feed); or treatment diets D-4 (3:1 Bacillus sp. SJ-10 and L. plantarum KCCM 11322 at 0.75 + 0.25 × 10⁸ CFU/g feed), D-5 (1:1 Bacillus sp. SJ-10 and L. plantarum KCCM 11322 at 0.50 + 0.50 × 10⁸ CFU/g feed), or D-6 (1:3 Bacillus sp. SJ-10 and L. plantarum KCCM 11322 at 0.25 + 0.75 × 10⁸ CFU/g feed) for 8 weeks. Group D-4 demonstrated better growth and feed utilization (P < 0.05) compared with the controls and positive controls. Similar modulation was also observed in respiratory burst for all treatments and in the expression levels of TNF-α, IL-1β, IL-6, and IL-10 in different organs in D-4. D-4 and D-5 increased respiratory burst, superoxide dismutase, lysozyme, and myeloperoxidase activities compared with the controls, and only D-4 increased microvilli length. When challenged with 1 × 10⁸ CFU/mL Streptococcus iniae, the fish in the D-4 and D-5 groups survived up to 14 days, whereas the fish in the other groups reached 100% mortality at 11.50 days. Collectively, a ratio-specific Bacillus sp. SJ-10 and L. plantarum KCCM 11322 mixture (3:1) was associated with elevated growth, innate immunity, and streptococcosis resistance (3:1 and 1:1) compared with the control and single probiotic diets.

The Impact of Sampling Season and Catching Site (Wild and Aquaculture) on Gut Microbiota Composition and Diversity of Nile Tilapia (Oreochromis niloticus)

Simple Summary

The gut microbiota (all microbes in the intestine) of fishes is known to play an essential role in diverse aspects of their life. The gut microbiota of fish is affected by various environmental parameters, including temperature changes, salinity and diet. This study characterised the microbial composition in gut samples of Nile Tilapia collected from Lake Tana and the Bahir Dar aquaculture facility centre applying modern molecular techniques. The results show clear differences in the gut microbiota in fish from the Lake Tana and the ones from aquaculture. Further, also significant differences were observed on the composition of the gut microbiota across sampling months. Samples from the aquaculture centre displayed a higher diversity than the wild catch Nile tilapia from Lake Tana even though there is also an overlapping of the detected microbial groups. Overall, this is the first study on the effects of sampling season and catching site on the gut microbiota of Nile tilapia in Ethiopia. Future work will help to precisely explain the causes of these changes and their influence of the health and growth of Nile tilapia in Ethiopian lakes as well as under aquaculture conditions.

Abstract

The gut microbiota of fishes is known to play an essential role in diverse aspects of host biology. The gut microbiota of fish is affected by various environmental parameters, including temperature changes, salinity and diet. Studies of effect of environment on gut microbiota enables to have a further understanding of what comprises a healthy microbiota under different environmental conditions. However, there is insufficient understanding regarding the effects of sampling season and catching site (wild and aquaculture) on the gut microbiota of Nile tilapia. This study characterised gut microbial composition and diversity from samples collected from Lake Tana and the Bahir Dar aquaculture facility centre using 16S rDNA Illumina MiSeq platform sequencing. Firmicutes and Fusobacteria were the most dominant phyla in the Lake Tana samples, while Proteobacteria was the most dominant in the aquaculture samples. The results of differential abundance testing clearly indicated significant differences for Firmicutes, Fusobacteria, Bacteroidetes and Cyanobacteria across sampling months. However, Proteobacteria, Chloroflexi, Fusobacteria and Cyanobacteria were significantly enriched in the comparison of samples from the Lake Tana and aquaculture centre. Significant differences were observed in microbial diversity across sampling months and between wild and captive Nile tilapia. The alpha diversity clearly showed that samples from the aquaculture centre (captive) had a higher diversity than the wild Nile tilapia samples from Lake Tana. The core gut microbiota of all samples of Nile tilapia used in our study comprised Firmicutes, Proteobacteria and Fusobacteria. This study clearly showed the impact of sampling season and catching site (wild and aquaculture) on the diversity and composition of bacterial communities associated with the gut of Nile tilapia. Overall, this is the first study on the effects of sampling season and catching site on the gut microbiota of Nile tilapia in Ethiopia. Future work is recommended to precisely explain the causes of these changes using large representative samples of Nile tilapia from different lakes and aquaculture farms.

Probiotic Shewanella putrefaciens (SpPdp11) as a Fish Health Modulator: A Review

Aquaculture is considered one of the largest food production sectors in the world. Probiotics have long been considered as a beneficial tool in this industry since these microorganisms improve the welfare of different fish species by modulating several physiological functions, such as metabolism, digestion, immune response, stress tolerance, and disease resistance, among others. SpPdp11, a probiotic isolated from the skin of healthy gilthead seabream, has been the center of attention in a good number of studies since its discovery. The purpose of this paper is to summarize, comment, and discuss the current knowledge related to the effects of SpPdp11 in two commercially important fish species in aquaculture (gilthead seabream and Senegalese sole). Furthermore, some considerations for future studies are also indicated.

Dual expression of transgenic delta-5 and delta-6 desaturase in tilapia alters gut microbiota and enhances resistance to Vibrio vulnificus infection

Omega-3 polyunsaturated fatty acids (n-3 PUFAs), such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), exhibit antibacterial and anti-inflammatory activities. Furthermore, diets rich in n-3 PUFAs are known to improve disease resistance and limit pathogen infection in commercial aquaculture fishes. In this study, we examined the effects of transgenic overexpression of n-3 PUFA biosynthesis genes on the physiological response to bacterial infection in tilapia. We first established tilapia strains with single or dual expression of salmon delta-5 desaturase and/or delta-6 desaturase and then challenged the fish with Vibrio vulnificus infection. Interestingly, our data suggest that n-3 PUFA-mediated alterations in gut microbiota may be important in determining disease outcome via effects on immune response of the host. Both liver- and muscle-specific single and dual expression of delta-5 desaturase and delta-6 desaturase resulted in higher n-3 PUFA content in transgenic fish fed with a LO basal diet. The enrichment of n-3 PUFAs in dual-transgenic fish is likely responsible for their improved survival rate and comparatively reduced expression of inflammation- and immune-associated genes after V. vulnificus infection. Gut microbiome analysis further revealed that dual-transgenic tilapia had high gut microbiota diversity, with low levels of inflammation-associated microbiota (i.e., Prevotellaceae). Thus, our findings indicate that dual expression of transgenic delta-5 and delta-6 desaturase in tilapia enhances disease resistance, an effect that is associated with increased levels of n-3 PUFAs and altered gut microbiota composition.

Effects of three host-associated Bacillus species on mucosal immunity and gut health of Nile tilapia, Oreochromis niloticus and its resistance against Aeromonas hydrophila infection

Skin and intestinal mucosa lymphoid tissues are known to be the fish's first line of defence since they serve as the first point of contact for pathogens. Only few studies have investigated the influence of host-associated Bacillus on mucosal immunity. In this study, the effects of three host-associated Bacillus species on mucosal immunity, intestinal morphology, intestinal digestive enzymes activity, intestinal microbiome and resistance of Nile tilapia against Aeromonas hydrophila infection was evaluated. The fish were divided into five treatment groups and fed with diets containing no bacteria denoted as Control, Bacillus velezensis TPS3N denoted as group V, Bacillus subtilis TPS4 denoted as group S, Bacillus amyloliquefaciens TPS17 denoted as group A and a 5^th group containing the three Bacillus species at a ratio 1:1:1 denoted as group CB. At the end of the feeding trial, significant enhancement of both skin mucus and intestinal immune titres were recorded in terms of nitric oxide (NO) (except in the mucus of V and S groups), immunoglobulin M (IgM) (except in the intestine of group V), lysozyme (LZM), and alkaline phosphatase (AKP) in all fish fed the Bacillus supplemented groups relative to the untreated group. Intestinal antioxidant enzymes (catalase (CAT) (except in the intestine of group S) and superoxide dismutase (SOD)) capacity of Nile tilapia were higher in the Bacillus groups. Intestinal lipase activity was elevated in the Bacillus supplemented groups. The intestinal morphological parameters (villus height, villus width, goblet cells count (except in group S and A), and intestinal muscle thickness) were significantly enhanced in the Bacillus supplemented groups relative to the Control group. Dietary probiotic supplementation also influenced the intestinal microflora composition of Nile tilapia. Proteobacteria recorded the highest abundance followed by Firmicutes, Fusobacteria, and Bacteroidetes at the phylum level in this study. At the genus level, the abundance of pathogenic bacteria viz Staphylococcus and Aeromonas were reduced in the Bacillus supplemented groups in comparison to the Control group. A challenge test with A. hydrophila resulted in lower mortalities (%) in the Bacillus treated groups thus 86.67%, 50.00%, 43.33%, 63.33%, and 30.00% for Nile tilapia fed Control, V, S, A, and CB diets respectively. In conclusion, the inclusion of B. velezensis TPS3N, B. subtilis TPS4, and B. amyloliquefaciens TPS17 in the diet of Nile tilapia singularly or in combination, could enhance the mucosal immunity, intestinal health, and resistance of Nile tilapia against A. hydrophila infection.

Comparative study on the effects of different feeding habits and diets on intestinal microbiota in Acipenser baeri Brandt and Huso huso

Background

Siberian sturgeon (Acipenser baeri Brandt) and Beluga sturgeon (Huso huso) are two important commercial fish in China, and the feeding habits of them are very different. Diets and feeding habits are two significant factors to affect the gastrointestinal microbiota in fish. The intestinal microbiota has been reported to play a key role in nutrition and immunity. However, it is rarely reported about the relationship between the intestinal microbiota and feeding habits/diets on different Acipenseridae fish. This study is to comparative analysis of gut microbial community in Siberian sturgeon and Beluga sturgeon fed with the same diet/Beluga sturgeon fed with different diets in order to determine the effects of different feeding habits/diets on the fish intestinal microbiota.

Results

According to the experimental objectives, BL and BH groups were Beluga sturgeon (Huso huso) fed with low fishmeal diet and high fishmeal diet, respectively. SH group represented Siberian sturgeon (Acipenser baeri Brandt) fed with the same diet as BH group. After 16 weeks feeding trial, the intestinal microbiota was examined by 16S rRNA high-throughput sequencing technology. On the phylum level, Proteobacteria and Bacteroidetes were significantly higher in BL group than BH group, and Cyanobacteria showed the opposite trend. Compared with BH group, Proteobacteria and Firmicutes were significantly increased in SH group, whereas Cyanobacteria were clearly decreased. At the genus level, Pseudomonas and Citrobacter in BL group were significantly higher comparing with BH group, while Bacillus, Luteibacter, Staphylococcus and Oceanobacillus was lower in BH group than SH group.

Conclusions

Alpha and beta diversities indicated that the intestinal microflora were significant difference between Siberian sturgeon and Beluga sturgeon when they fed with the same diet. Meanwhile, Beluga sturgeon fed with low fishmeal diet can increase the species diversity of intestinal microbiota than it fed high fishmeal diet. Therefore, feeding habits clearly affected the gastrointestinal microbiota of sturgeons. Moreover, the impact of changes in food on the gut microbiota of sturgeons should be taken into consideration during the process of sturgeon aquaculture.

The effect of dietary supplementation with Clostridium butyricum on the growth performance, immunity, intestinal microbiota and disease resistance of tilapia (Oreochromis niloticus)

This study was conducted to assess the effects of dietary Clostridium butyricum on the growth, immunity, intestinal microbiota and disease resistance of tilapia (Oreochromis niloticus). Three hundreds of tilapia (56.21 ± 0.81 g) were divided into 5 groups and fed a diet supplemented with C. butyricum at 0, 1 x 10⁴, 1 x 10⁵, 1 x 10⁶ or 1 x 10⁷ CFU g^-1 diet (denoted as CG, CB1, CB2, CB3 and CB4, respectively) for 56 days. Then 45 fish from each group were intraperitoneally injected with Streptococcus agalactiae, and the mortality was recorded for 14 days. The results showed that dietary C. butyricum significantly improved the specific growth rate (SGR) and feed intake in the CB2 group and decreased the cumulative mortality post-challenge with S. agalactiae in the CB2, CB3 and CB4 groups. The serum total antioxidant capacity and intestinal interleukin receptor-associated kinase-4 gene expression were significantly increased, and serum malondialdehyde content and diamine oxidase activity were significantly decreased in the CB1, CB2, CB3 and CB4 groups. Serum complement 3 and complement 4 concentrations and intestinal gene expression of tumour necrosis factor α, interleukin 8, and myeloid differentiation factor 88 were significantly higher in the CB2, CB3 and CB4 groups. Intestinal toll-like receptor 2 gene expression was significantly upregulated in the CB3 and CB4 groups. Dietary C. butyricum increased the diversity of the intestinal microbiota and the relative abundance of beneficial bacteria (such as Bacillus), and decreased the relative abundance of opportunistic pathogenic bacteria (such as Aeromonas) in the CB2 group. These results revealed that dietary C. butyricum at a suitable dose enhanced growth performance, elevated humoral and intestinal immunity, regulated the intestinal microbial components, and improved disease resistance in tilapia. The optimal dose was 1 x 10⁵ CFU g^-1 diet.

Effects of dietary multi-strain probiotics supplementation in a low fishmeal diet on growth performance, nutrient utilization, proximate composition, immune parameters, and gut microbiota of juvenile olive flounder (Paralichthys olivaceus)

A 12-week feeding trial was conducted to evaluate the effects of multi-strain probiotics (MSP) in a low fish meal (FM) diet on overall performance, gut microbiota, selected non-specific immune responses and antioxidant enzyme activities of olive flounder (Paralichthys olivaceus) juveniles. A total of 225 healthy olive flounders (initial mean body weight, 13.5 ± 0.01 g) were randomly separated into 3 groups of 75 fish, each group having three replicates of 25 fish; first group was fed with a FM-based control diet (Con), 2nd group was fed with a low-FM diet containing a blend of plant and animal protein meals replacing 30% of the FM protein (FM30), and 3rd group was fed with the FM30 diet supplemented with 10⁸-10⁹ CFU kg^-1 of the MSP (Pro). With the exception of lipid retention, which was significantly lower in fish fed the FM30 diet compared to the other two treatments, no other statistically significant differences were recorded with respect to any of the other growth and nutrient utilization parameters. Myeloperoxidase and lysozyme activities of fish fed the Pro diet were much higher and significantly different than those of fish fed the FM30 diet. Glutathione peroxidase activity was significantly higher in Pro- than in Con-fed fish, which, in turn, was significantly higher than FM30-fed fish. Expression of immune-related genes including IL-1β, IL-6, and TNF-α was markedly upregulated in livers of the fish fed Pro diet compared to those fed the Con and FM30 diets. Furthermore, supplementation of MSP in FM30 diet enriched the Lactobacillus abundance in the fish gut as well as predictive gene functions in relation to lipid and carbohydrate metabolisms. These data suggested that the MSP could reduce the potential adverse effects of the low-FM diet and might be used as a healthy immunostimulant for olive flounder.

Improvements in the growth performance, immunity, disease resistance, and gut microbiota by the probiotic Rummeliibacillus stabekisii in Nile tilapia (Oreochromis niloticus)

The application of probiotics as an eco-friendly alternative to antibiotics is an emerging strategy for sustainable aquaculture. In the present study, Rummeliibacillus stabekisii was isolated from the gut of Nile tilapia, and the effects of R. stabekisii on the growth, innate immunity, disease resistance, and gut microbiota of Nile tilapia (Oreochromis niloticus) were investigated. The results showed significantly increased weight gain (WG), feed conversion ratio (FCR), and feed efficiency (FE) in Nile tilapia fed R. stabekisii for 8 weeks compared to those in fish fed a control diet. Intestinal digestive enzymes such as protease, cellulase, and xylanase were also significantly increased in the R. stabekisii-administered groups. Enhanced cumulative survival was exhibited in fish fed R. stabekisii after challenge with Aeromonas hydrophila and Streptococcus iniae. Immune parameters such as the phagocytic activity, respiratory bursts, and superoxide dismutase of head kidney leukocytes; serum lysozyme activity; and expression of the cytokine genes interleukin-1β, tumor necrosis factor-α, transforming growth factor-β, and heat shock protein 70 were significantly elevated in fish fed R. stabekisii. Administration of R. stabekisii considerably increased the abundance of potential probiotics (Bacillus and Lactobacillus spp.) and reduced abundances of potential pathogenic bacteria (Streptococcus and Staphylococcus spp.) in fish intestines. The present study indicated that dietary supplementation with R. stabekisii improved the growth, immunity, disease resistance, and gut microflora of Nile tilapia. This research is the first study reporting that the genus Rummeliibacillus is a potential probiotic in animals, suggesting that R. stabekisii can be used as a feed additive to enhance the growth and health status in tilapia.

Effects of dietary probiotic supplementation on the growth, gut health and disease resistance of juvenile Nile tilapia (Oreochromis niloticus)

This study investigated the effects of the Streptococcus agalactiae antagonizing probiotics Bacillus cereus NY5 and Bacillus subtilis as feed additives for Nile tilapia in terms of growth performance, intestinal health and resistance to S. agalactiae. A total of 720 apparently healthy juvenile Nile tilapia (0.20 ± 0.05 g) were randomly divided into 4 equal groups with 3 replicates for each group. Fish were fed a basal diet (control check group, CK group) supplemented with B. subtilis (1 × 10⁸ CFU/g feed, BS group), B. cereus NY5 (1 × 10⁸ CFU/g feed, BC group), and B. subtilis + B. cereus NY5 (0.5 × 10⁸ CFU/g feed of each probiotic, BS + BC group) for 6 wk, and the probiotic supplementation groups were then fed the basal diet for 1 wk to investigate the gut microbial community. The results of this study showed that BS + BC and BC treatments significantly increased weight gain (WG), feed conversion ratio (FCR) and S. agalactiae resistance in Nile tilapia (P < 0.05). Gut microvilli length and density and c-type lysozyme (lyzc) gene expression were significantly increased by probiotic supplementation (P < 0.05). The results of high-throughput sequencing showed that the B. cereus NY5 and B. subtilis + B. cereus NY5-supplemented feed resulted in a significant improvement in tilapia autochthonous gut bacterial communities and had a stimulation effect on a variety of potential probiotics after 6 wk of feeding. After cessation of probiotic administration for 1 wk, the gut bacteria of the fish in the BS + BC and BC groups had minor changes and maintained a stable state. Consequently, it was inferred that, as a feed supplement, B. cereus NY5 and the mixture of B. subtilis and B. cereus NY5 at 1 × 10⁸ CFU/g feed were able to promote growth and disease resistance, which may be associated with the supplement's effects on gut immune status, intestinal morphology, and intestinal microbial community composition.

The effect of a multi-strain probiotic on growth performance, non-specific immune response, and intestinal health of juvenile turbot, Scophthalmus maximus L

Probiotic is well known because of its health benefit on the host, including improve growth, treat disease, and enhance immunity. Currently, probiotic has been widely used in aquaculture. However, there is little information about the effect of probiotic on turbot. Therefore, an effort was made to explore the effect of a multi-strain probiotic on growth performance, non-specific immune response, and intestinal health of juvenile turbot, Scophthalmus maximus L. One hundred eighty juvenile turbot (20.04 ± 0.23 g) were randomly divided into three groups (T0, T1, T2), and fed diet were formulated to contain 0%, 1%, and 5% multi-strain probiotic, respectively. Sixty days after the feeding experiment, the growth performance, body composition, enzyme activities, and intestinal microorganism of turbot were analyzed. T2 and T1 showed better growth performance and significant higher (P < 0.05) enzyme activities than T0 (except lysozyme). Moreover, the IV (intestinal villus), IW (intestinal wall), and GC (goblet cell) were well modulated in probiotic treatments. Furthermore, Lactobacillus was found colonized in the intestine of the group fed with 5% multi-strain probiotic. These results suggested adding dietary multi-strain probiotic could positively affect for turbot aquaculture.

Effects of dietary mixed probiotics on growth, non-specific immunity, intestinal morphology and microbiota of juvenile pacific white shrimp, Litopenaeus vannamei

This study was conducted to elucidate the effects of dietary mixed probiotics on growth, non-specific immunity, intestinal morphology and microbiota of juvenile pacific white shrimp, Litopenaeus vannamei. Juvenile shrimp (initial body weight 1.21 ± 0.01 g) were fed diets containing graded probiotics (F1: 0 mg/kg probiotics; F2: 1000 mg/kg probiotics; F3: 2000 mg/kg probiotics; F4: 4000 mg/kg compound probiotics; F5: 6000 mg/kg probiotics; F6: 8000 mg/kg probiotics) for 8 weeks. The result of this trial showed that the growth performance (SGR, WG, FBW) of shrimp fed diets containing probiotics (F2∼F6) were significantly higher than that of shrimp fed diet without supplemental probiotics (F1) (P < 0.05), and the highest values of the growth performance (SGR, WG, FBW) and lowest FCR were found in shrimp fed the diet containing 2000 mg/kg probiotics. Total antioxidant capacity of shrimp fed diet F2 and F3 were significantly higher than that of shrimp fed the basal diets (P < 0.05). Superoxide dismutase in F4 treatment was significantly higher than that of basal treatment (P < 0.05). Catalase of shrimp in all probiotics supplemented (F2∼F6) treatments were significantly higher than that of the control one (F1) (P < 0.05). Malondialdehyde in F5 groups was significantly lower than that of F1 groups (P < 0.05). Alkline phosphatase and acid phosphatase in F3 treatments were significantly higher than those of the basal one (P < 0.05). Lysozyme of shrimp fed F2∼F6 were significantly higher than that of shrimp fed F1 diet (P < 0.05). The lipase and amylase activities in 2000 mg/kg probiotics groups showed the highest activities and were significantly higher than that of control one (P < 0.05). Intestinal villi height in F3∼F6 treatments were significantly higher than that of control one (P < 0.05). Alpha diversity indices including observed species, chao1, ACE and shannon indices showed that F2 and F3 groups had higher microbial diversity in their intestines, both richness and evenness. PCA plot showed that there was a clear shift of F2 and F3 groups from the control groups in microbial community structure. The dominant phyla in pacific white shrimp are proteobacteria, bacteroidetes and actinobacteria, the dominant genus were algoriphagus and vibrio. As the probiotics increased, the gemmatimonadetes, acidobacteria, deltaproteobacteria and xanthomonadales firstly increased and then decreased, with the highest content in F2 group, which was no significant difference to F3 group (P > 0.05) while significantly higher than other groups (P < 0.05). In conclusion, the supplement of mixed species probiotics can promote growth performance, enhance the non-specific immunity, influence the microbiota of the pacific white shrimps and the recommended optimum dosage in diet of Litopenaeus vannamei was 2000 mg/kg.

Dietary supplementation with probiotics regulates gut microbiota structure and function in Nile tilapia exposed to aluminum

BACKGROUNDS AND AIMS

Aluminum contamination of water is becoming increasingly serious and threatens the health status of fish. Lactobacillus plantarum CCFM639 was previously shown to be a potential probiotic for alleviation aluminum toxicity in Nile tilapia. Considering the significant role of the gut microbiota on fish health, it seems appropriate to explore the relationships among aluminum exposure, probiotic supplementation, and the gut microbiota in Nile tilapia and to determine whether regulation of the gut microbiota is related to alleviation of aluminum toxicity by a probiotic in Nile tilapia.

METHODS AND RESULTS

The tilapia were assigned into four groups, control, CCFM639 only, aluminum only, and aluminum + CCFM639 groups for an experimental period of 4 weeks. The tilapia in the aluminum only group were grown in water with an aluminum ion concentration of 2.73 mg/L. The final concentration of CCFM639 in the diet was 108 CFU/g. The results show that environmental aluminum exposure reduced the numbers of L. plantarum in tilapia feces and altered the gut microbiota. As the predominant bacterial phyla in the gut, the abundances of Bacteroidetes and Proteobacteria in aluminum-exposed fish were significantly elevated and lowered, respectively. At the genus level, fish exposed to aluminum had a significantly lower abundance of Deefgea, Plesiomonas, and Pseudomonas and a greater abundance of Flavobacterium, Enterovibrio, Porphyromonadaceae uncultured, and Comamonadaceae. When tilapia were exposed to aluminum, the administration of a probiotic promoted aluminum excretion through the feces and led to a decrease in the abundance of Comamonadaceae, Enterovibrio and Porphyromonadaceae. Notably, supplementation with a probiotic only greatly decreased the abundance of Aeromonas and Pseudomonas.

CONCLUSION

Aluminum exposure altered the diversity of the gut microbiota in Nile tilapia, and probiotic supplementation allowed the recovery of some of the diversity. Therefore, regulation of gut microbiota with a probiotic is a possible mechanism for the alleviation of aluminum toxicity in Nile tilapia.

Bacterial Community Dynamics in an Oyster Hatchery in Response to Probiotic Treatment

Larval oysters in hatcheries are susceptible to diseases caused by bacterial pathogens, including Vibrio spp. Previous studies have shown that daily addition of the probiotic Bacillus pumilus RI06-95 to water in rearing tanks increases larval survival when challenged with the pathogen Vibrio coralliilyticus. We propose that the presence of probiotics causes shifts in bacterial community structure in rearing tanks, leading to a net decrease in the relative abundance of potential pathogens. During three trials spanning the 2012-2015 hatchery seasons, larvae, tank biofilm, and rearing water samples were collected from control and probiotic-treated tanks in an oyster hatchery over a 12-day period after spawning. Samples were analyzed by 16S rRNA sequencing of the V4 or V6 regions followed by taxonomic classification, in order to determine bacterial community structures. There were significant differences in bacterial composition over time and between sample types, but no major effect of probiotics on the structure and diversity of bacterial communities (phylum level, Bray-Curtis k = 2, 95% confidence). Probiotic treatment, however, led to a higher relative percent abundance of Oceanospirillales and Bacillus spp. in water and oyster larvae. In the water, an increase in Vibrio spp. diversity in the absence of a net increase in relative read abundance suggests a likely decrease in the abundance of specific pathogenic Vibrio spp., and therefore lower chances of a disease outbreak. Co-occurrence network analysis also suggests that probiotic treatment had a systemic effect on targeted members of the bacterial community, leading to a net decrease in potentially pathogenic species.

The intestinal environment as an evolutionary adaptation to mouthbrooding in the Astatotilapia burtoni cichlid

Many of the various parental care strategies displayed by animals are accompanied by a significant reduction in food intake that imposes a substantial energy trade-off. Mouthbrooding, as seen in several species of fish in which the parent holds the developing eggs and fry in the buccal cavity, represents an extreme example of reduced food intake during parental investment and is accompanied by a range of physiological adaptations. In this study we use 16S sequencing to characterize the gut microbiota of female Astatotilapia burtoni cichlid fish throughout the obligatory phase of self-induced starvation during the brooding cycle in comparison to stage-matched females that have been denied food for the same duration. In addition to a reduction of gut epithelial turnover, we find a dramatic reduction in species diversity in brooding stages that recovers upon release of fry and refeeding that is not seen in females that are simply starved. Based on overall species diversity as well as differential abundance of specific bacterial taxa, we suggest that rather than reflecting a simple deprivation of caloric intake, the gut microbiota is more strongly influenced by physiological changes specific to mouthbrooding including the reduced epithelial turnover and possible production of antimicrobial agents.

Effects of Lactococcus lactis subsp. lactis JCM5805 on colonization dynamics of gut microbiota and regulation of immunity in early ontogenetic stages of tilapia

The administration of probiotics during early ontogenetic stages can be an effective way to manipulate the gut microbiota of animals. Specifically, the administration of probiotics can enhance gut-colonization success and regulate the immune response. In this study, the effects of early contact with probiotic Lactococcus lactis subsp. lactis JCM5805 on the gut microbial assembly of larvae Nile tilapia were examined. The effects of JCM5805 on IFNα expression through the TLR7 and TLR9-dependent signal transduction pathway as well as larval disease resistance were studied. Three days postfertilization, embryos were randomly allocated into nine 30 L tanks with a concentration of 20 eggs L^-1. Triplicate tanks were performed for each treatment. Treatments included a control group (C), a low probiotic concentration group (T1), where JCM5805 was added to the water at 1 × 10⁴ cfu ml^-1, and a high probiotic concentration group (T2), where JCM5805 was added to the water at 1 × 10⁸ cfu ml^-1. Probiotics were administered continuously for 15 days. qPCR was used to analyze transcript levels of the TLR7, TLR9, MyD88, IRF7 and IFNα genes using RNA extracted from whole embryos on day 5 and 10, and from the intestine of larvae on day 15. Transcription of these genes was also measured in the intestine, liver and spleen of larvae one month after the cessation of probiotic administration. The results showed that MyD88 and IRF7 were significantly elevated on days 5 and 10 in the T2 group. TLR9 and IFNα were also significantly elevated on days 5, 10 and 15 during probiotic application of T2 (P < 0.05). One month after the cessation of probiotics administration, no significant difference was observed in the expression of these genes (P > 0.05). The larvae were fed probiotics for 15 days and were infused with Streptococcus agalactiae strain WC1535 at a final concentration of 1 × 10⁶ cfu ml^-1. The survival rate of T2 was significantly higher than that of the C group (P < 0.05). Microbial characterization by Illumina HiSeq sequencing of 16S rRNA gene amplicons showed the significantly higher presence of JCM5805 in the guts of T2 after 15 days of probiotic continuous application. Although JCM5805 was below the detection level after the cessation of probiotic for 5 days, the gut microbiota of the exposed tilapia larvae in T2 remained clearly different from that of the control treatment after the cessation of probiotic administration. These data indicated that a high concentration of the probiotic strain JCM5805 upregulated the expression of IFNα via the TLR7/TLR9-Myd88 pathway and enhanced disease resistance of larvae. JCM5805 was only transiently detected and thus was not included in the stable larval microbiota. The early microbial exposure of tilapia larvae affects the gut microbiota at later life stages. However, whether the upregulation of related genes is related to the presence of JCM5805 strain in the intestine requires further verification.

Gut Microbiota and Energy Homeostasis in Fish

The microorganisms within the intestinal tract (termed gut microbiota) have been shown to interact with the gut-brain axis, a bidirectional communication system between the gut and the brain mediated by hormonal, immune, and neural signals. Through these interactions, the microbiota might affect behaviors, including feeding behavior, digestive/absorptive processes (e.g., by modulating intestinal motility and the intestinal barrier), metabolism, as well as the immune response, with repercussions on the energy homeostasis and health of the host. To date, research in this field has mostly focused on mammals. Studies on non-mammalian models such as fish may provide novel insights into the specific mechanisms involved in the microbiota-brain-gut axis. This review describes our current knowledge on the possible effects of microbiota on feeding, digestive processes, growth, and energy homeostasis in fish, with emphasis on the influence of brain and gut hormones, environmental factors, and inter-specific differences.

Effects of Lactogen 13, a New Probiotic Preparation, on Gut Microbiota and Endocrine Signals Controlling Growth and Appetite of Oreochromis niloticus Juveniles

In the present study, Nile tilapia Oreochromis niloticus was used as experimental model to study the molecular effects of a new probiotic preparation, Lactogen 13 (Lactobacillus rhamnosus IMC 501® encapsulated with vegetable fat matrices by spray chilling and further indicated as probiotic microgranules), on growth and appetite during larval development. Probiotic microgranules were administered for 30 days to tilapia larvae starting from first feeding. Molecular analysis using high-throughput sequencing revealed that the probiotic could populate the gastrointestinal tract and modulate the microbial communities by significantly increasing the proportion of Lactobacillus as well as reducing the proportion of potential pathogens such as members of the Family Microbacteriaceae, Legionellaceae, and Weeksellaceae. Morphometric analysis evidenced that body weight and total length significantly increased after probiotic treatment. This increase coincided with the modulation of genes belonging to the insulin-like growth factors (igfs) system and genes involved on myogenesis, such as myogenin, and myogenic differentiation (myod). Alongside the improvement of growth, an increase of feed intake was evidenced at 40 days post-fertilization (dpf) in treated larvae. Gene codifying for signals belonging to the most prominent systems involved in appetite regulation, such as neuropeptide y (npy), agouti-related protein (agrp), leptin, and ghrelin were significantly modulated. These results support the hypothesis that gastrointestinal (GI) microbiota changes due to probiotic administration modulate growth and appetite control, activating the endocrine system of tilapia larvae.

Lactic Acid Bacteria in Finfish-An Update

A complex and dynamic community of microorganisms, play important roles within the fish gastrointestinal (GI) tract. Of the bacteria colonizing the GI tract, are lactic acid bacteria (LAB) generally considered as favorable microorganism due to their abilities to stimulating host GI development, digestive function, mucosal tolerance, stimulating immune response, and improved disease resistance. In early finfish studies, were culture-dependent methods used to enumerate bacterial population levels within the GI tract. However, due to limitations by using culture methods, culture-independent techniques have been used during the last decade. These investigations have revealed the presence of Lactobacillus, Lactococcus, Leuconostoc, Enterococcus, Streptococcus, Carnobacterium, Weissella, and Pediococcus as indigenous species. Numerous strains of LAB isolated from finfish are able to produce antibacterial substances toward different potential fish pathogenic bacteria as well as human pathogens. LAB are revealed be the most promising bacterial genera as probiotic in aquaculture. During the decade numerous investigations are performed on evaluation of probiotic properties of different genus and species of LAB. Except limited contradictory reports, most of administered strains displayed beneficial effects on both, growth-and reproductive performance, immune responses and disease resistance of finfish. This eventually led to industrial scale up and introduction LAB-based commercial probiotics. Pathogenic LAB belonging to the genera Streptococcus, Enterococcus, Lactobacillus, Carnobacterium, and Lactococcus have been detected from ascites, kidney, liver, heart, and spleen of several finfish species. These pathogenic bacteria will be addressed in present review which includes their impacts on finfish aquaculture, possible routes for treatment. Finfish share many common structures and functions of the immune system with warm-blooded animals, although apparent differences exist. This similarity in the immune system may result in many shared LAB effects between finfish and land animals. LAB-fed fish show an increase in innate immune activities leading to disease resistances: neutrophil activity, lysozyme secretion, phagocytosis, and production of pro-inflammatory cytokines (IL-1β, IL-6, IL-8, and TNF-α). However, some LAB strains preferentially induces IL-10 instead, a potent anti-inflammatory cytokine. These results indicate that LAB may vary in their immunological effects depending on the species and hosts. So far, the immunological studies using LAB have been focused on their effects on innate immunity. However, these studies need to be further extended by investigating their involvement in the modulation of adaptive immunity. The present review paper focuses on recent findings in the field of isolation and detection of LAB, their administration as probiotic in aquaculture and their interaction with fish immune responses. Furthermore, the mode of action of probiotics on finfish are discussed.

Effects of dietary Lactobacillus rhamnosus JCM1136 and Lactococcus lactis subsp. lactis JCM5805 on the growth, intestinal microbiota, morphology, immune response and disease resistance of juvenile Nile tilapia, Oreochromis niloticus

The present study aimed to evaluate the individual and combined effects of Lactobacillus rhamnosus (LR) JCM1136 and Lactococcus lactis subsp. lactis (LL) JCM5805 on the growth, intestinal microbiota, intestinal morphology, immune response and disease resistance of juvenile Nile tilapia (Oreochromis niloticus). A total of 720 apparently healthy juvenile Nile tilapia (0.20 ± 0.05 g) were randomly divided into four equal groups. Fish were fed with a basal diet (CK) supplemented with JCM1136 (LR), JCM5805 (LL), and JCM1136 + JCM5805 (LR+LL) at 1 × 10⁸ CFU/g basal diet for 6 weeks, followed by a basal diet for 1 week. After 6 weeks of feeding, the LL treatment significantly increased the growth and feed utilization of Nile tilapia when compared with the CK. Light microscopy and transmission electron microscopy images of the midgut revealed that probiotic supplementation significantly increased gut microvilli length and microvilli density compared to CK. The transcript levels of several key immune-related genes in the mid-intestine and liver of fish were analyzed by means of quantitative polymerase chain reaction (qPCR) at the end of the sixth week. The results showed the following: when compared to CK group, fish in LR had significantly increased transcript levels of IFN-γ, lyzc, hsp70 and IL-1β in the intestine; LL fish showed significantly increased expressions of TNF-α, IFN-γ, lyzc, hsp70 and IL-1β in the intestine and liver; and intestine lyzc, hsp70 and IL-1β and liver TNF-α, IFN-γ, hsp70 and IL-1β were significantly increased in LR+LL fish. Following a 6-week period of being fed probiotics or a control diet, the tilapia were challenged with an intraperitoneal injection of 20 μl of the pathogenic Streptococcus agalactiae (WC1535) (1 × 10⁵ CFU/ml). The survival rates of the probiotic-fed groups were significantly higher than that of the CK group, and the LL group had the highest survival rate. High-throughput sequencing revealed a significantly higher presence of JCM5805 in the guts of LL fish during the period of probiotic application, but this was no longer detected in all LL samples 1 week post cessation of probiotic administration. Cessation of probiotic administration led to disorders of individual gut microbes within the LR and LL groups. Statistical analysis (LEfSe) demonstrated that three phyla, namely, Bacteroidetes, Fusobacteria and Actinobacteria were enriched in the CK group, while the abundance of Proteobacteria was greater in the probiotic-fed fish. At the genus level, Plesiomonas, which includes potential pathogens of fish, were significantly decreased in the probiotic-fed groups. In contrast, a significant increase of Rhizobium and Achromobacter, which can produce a variety of enzymes with cellulolytic and pectolytic activity, were observed in fish fed with probiotics, indicating that dietary probiotics were helpful in the propagation of some probiotic bacteria. Our data revealed that JCM1136 and JCM5805, as a feed additive at 10⁸ CFU/g feed, could improve intestinal morphology, enhance immune status and disease resistance, and affect the gut microbiota of tilapia; thus, these additives could be used as probiotics for juvenile Nile tilapia. JCM5805 was more effective than JCM1136 or the mixture of the two for promoting the growth, enhancing the immune status and disease resistance of tilapia.

Treatment With High-Hydrostatic Pressure, Activated Film Packaging With Thymol Plus Enterocin AS-48, and Its Combination Modify the Bacterial Communities of Refrigerated Sea Bream (Sparus aurata) Fillets

The aim of this study was to determine the impact of activated plastic films with thymol and enterocin AS-48 and high-hydrostatic pressure (HP) treatment on the bacterial load and bacterial diversity of vacuum-packaged sea bream fillets under refrigerated storage for 10 days. The activated film and the HP treatment reduced aerobic mesophiles viable counts by 1.46 and 2.36 log cycles, respectively, while the combined treatment achieved a reduction of 4.13 log cycles. HP and combined treatments resulted in longer delays in bacterial growth. Proteobacteria were the dominant phyla in sea bream fillets. The relative abundance of Firmicutes increased by the end of storage both in controls and in samples treated by HP singly or in combination with the activated films. The predominant operational taxonomic units (OTUs) found at time 0 in control samples (Listeria, Acinetobacter, Pseudomonas, Enterobacteriaceae, Chryseobacterium) rapidly changed during storage (with an increase of Vibrio, Photobacterium, and Shewanella together with Cloacibacterium and Lactobacillales by the end of storage). The activated film and the HP treatment induced drastic changes in bacterial diversity right after treatments (with Comamonadaceae, Methylobacterium, Acidovorax, and Sphingomonas as main OTUs) and also induced further modifications during storage. Bacterial diversity in activated film samples was quite homogeneous during storage (with Vibrio, Photobacterium, and Shewanella as main OTUs) and approached control samples. HP treatments (singly or in combination with activated films) determined a high relative abundance of Acinetobacter (followed by Pseudomonas and Shewanella) during early storage as well as a higher relative abundance of lactic acid bacteria by the end of storage. The results indicate that the complex dynamics of bacterial populations in the refrigerated sea bream fillets are markedly influenced by treatment and antimicrobials applied.

Stochastic Individual-Based Modeling of Bacterial Growth and Division Using Flow Cytometry

A realistic description of the variability in bacterial growth and division is critical to produce reliable predictions of safety risks along the food chain. Individual-based modeling of bacteria provides the theoretical framework to deal with this variability, but it requires information about the individual behavior of bacteria inside populations. In this work, we overcome this problem by estimating the individual behavior of bacteria from population statistics obtained with flow cytometry. For this objective, a stochastic individual-based modeling framework is defined based on standard assumptions during division and exponential growth. The unknown single-cell parameters required for running the individual-based modeling simulations, such as cell size growth rate, are estimated from the flow cytometry data. Instead of using directly the individual-based model, we make use of a modified Fokker-Plank equation. This only equation simulates the population statistics in function of the unknown single-cell parameters. We test the validity of the approach by modeling the growth and division of Pediococcus acidilactici within the exponential phase. Estimations reveal the statistics of cell growth and division using only data from flow cytometry at a given time. From the relationship between the mother and daughter volumes, we also predict that P. acidilactici divide into two successive parallel planes.