The Application of Bacillus subtilis for Adhesion Inhibition of Pseudomonas and Preservation of Fresh Fish

Transcriptome Analysis Reveals the Molecular Mechanism of Pseudomonas with Different Adhesion Abilities on Tilapia Decay

This study aimed to investigate the molecular mechanism of Pseudomonas with varying adhesion capabilities to Tilapia's intestinal mucus influence the spoilage potential of Tilapia. Sodium chloride(NaCl) was used as an environmental factor to regulate Pseudomonas' adhesion ability. After being exposed to 3.5% NaCl stress, the PS01 strain with low adhesion showed an enhancement in adhesion ability, while the LP-3 strain with high adhesion exhibited a decrease. Correspondingly, the expression of critical adhesion genes, such as flgC, fliC, and cheB, was found to be altered. LP-3, with high adhesion ability, was observed to promote a relative increase in Nocardioides and Cloacibacterium in fish intestines. This led to the production of more volatile compounds, including 2-octen-1-ol Z, 2,3-Octanedione, and Eicosane, thus deepening the spoilage of tilapia. LP-3, with reduced adhesion ability after NaCl regulation, showed a diminished capacity to cause fish spoilage. Transcriptomics analysis was used to examine two Pseudomonas strains that exhibited different adhesion abilities, leading to the identification of an adhesion regulatory network involving flagellar assembly regulation, bacterial chemotaxis, quorum sensing, two-component systems, biofilm formation, and bacterial secretion systems. This study identified the Pseudomonas adhesion regulatory pathway and determined 10 key adhesion-related genes.

New advances in biological preservation technology for aquatic products

Aquatic products, characterized by their high moisture content, abundant nutrients, and neutral pH, create an optimal environment for the rapid proliferation of spoilage organisms, lipid oxidation, and autolytic degradation. These factors collectively expedite the spoilage and deterioration of aquatic products during storage and transportation within the supply chain. To maintain the quality and extend the shelf-life of aquatic products, appropriate preservation methods must be implemented. The growing consumer preference for bio-preservatives, is primarily driven by consumer demands for naturalness and concerns about environmental sustainability. The present review discusses commonly employed bio-preservatives derived from plants, animals, and microorganisms and their utilization in the preservation of aquatic products. Moreover, the preservation mechanisms of bio-preservatives, including antioxidant activity, inhibition of spoilage bacteria and enzyme activity, and the formation of protective films are reviewed. Integration of bio-preservation techniques with other methods, such as nanotechnology, ozone technology, and coating technology that enhance the fresh-keeping effect are discussed. Importantly, the principal issues in the application of bio-preservation technology for aquatic products and their countermeasures are presented. Further studies and the identification of new bio-preservatives that preserve the safety and quality of aquatic products should continue.

Revealing the optimal traditional processing methods and its protective effects against febrile seizures of Arisaema cum bile

Arisaema cum bile (known as Dan Nanxing in Chinese, DNX) is a herbal medicine used for treating febrile seizure (FS), which commonly prepared by using Arisaematis Rhizoma and animal bile. This study was designed to explore the optimal processing time of DNX and its potential mechanism on the anti-FS effect. A total of 17 volatile organic compounds (VOCs) were the characteristic ones to distinguish different fermentation stages of DNX by using gas chromatography-ion mobility spectrometry (GC-IMS), such as 2-heptanone monomer, and heptanal monomer. DNX with fermentation for 3 months had an obvious pattern of VOCs with others, which could be regarded as the optimal fermentation time. The Enterococcus and Staphylococcus might be the core bacteria on the production of VOCs. Additionally, DNX (2.8 g/kg, p.o.) reversed hot water bath-induced FSs of rats, as indicated by increased seizure latency and decreased seizure duration time. It also prevented hippocampal neuronal loss, increased GABAAR, and decreased GRIA1 expression. At the genus level, relative abundance of Enterococcus and Akkermansia were enriched after DNX treatment. These findings suggested that fermentation for 3 months might be the optimal process time for DNX, and DNX possess an anti-FS effect through regulating neurotransmitter disorder and gut microbiota.

Stochastic processes shape microbial community assembly in biofilters: Hidden role of rare taxa

Stochastic and deterministic processes are the major themes governing microbial community assembly; however, their roles in bioreactors are poorly understood. Herein, the mechanisms underlying microbial assembly and the effect of rare taxa were studied in biofilters. Phylogenetic tree analysis revealed differences in microbial communities at various stages. Null model analysis showed that stochastic processes shaped the community assembly, and deterministic processes emerged only in the inoculated activated sludge after domestication. This finding indicates the dominant role of stochastic factors (biofilm formation, accumulation, and aging). The Sloan neutral model corroborated the advantages of stochastic processes and mainly attributed these advantages to rare taxa. Cooccurrence networks revealed the importance of rare taxa, which accounted for more than 85% of the keystones. Overall, these results provide good foundations for understanding community assembly, especially the role of rare taxa, and offer theoretical support for future community design and reactor regulation.

Strain-Specific Benefits of Bacillus Probiotics in Hybrid Grouper: Growth Enhancement, Metabolic Health, Immune Modulation, and Vibrio harveyi Resistance

In the realm of modern aquaculture, the utilization of probiotics has gained prominence, primarily due to their ability to enhance growth, boost immunity, and prevent diseases in aquatic species. This study primarily investigates the efficacy of Bacillus subtilis strains, both host-derived and from other sources, in influencing fish growth, immunity, lipid metabolism, and disease resistance. Employing a 42-day feeding trial, we divided hybrid grouper into four distinct groups: a control group on a basal diet and three experimental groups supplemented with 1 × 108 CFU/g of different Bacillus subtilis strains-BS, 6-3-1, and HAINUP40. Remarkably, the study demonstrated that the 6-3-1 and HAINUP40 groups exhibited significant enhancements across key growth parameters: final body weight (FBW), weight gain rate (WGR), feed intake (FI), feed efficiency ratio (FER), and feed conversion ratio (FCR). The investigation into lipid metabolism revealed that the 6-3-1 strain upregulated seven metabolism-related genes, HAINUP40 affected four metabolism-related genes, and the BS strain influenced two metabolism-related genes, indicating diverse metabolic impacts by different strains. Further, a notable reduction in liver enzymes AST and ALT was observed across all supplemented groups, implying improved liver health. Noteworthy was the BS strain's superior antioxidative capabilities, positively affecting all four measured parameters (CAT, GSH-Px, MDA). In the sphere of immune-related gene expression, the BS strain significantly decreased the expression of both inflammation and apoptosis-related genes, whereas the HAINUP40 strain demonstrated an upregulation in these genes. The challenge test results were particularly telling, showcasing improved survival rates against Vibrio harveyi infection in the BS and 6-3-1 groups, unlike the HAINUP40 group. These outcomes highlight the strain-specific nature of probiotics and their varying mechanisms of action within the host. In conclusion, this study reveals that probiotic strains, varying by source, demonstrate unique, strain-specific effects in promoting growth and modulating immunity in hybrid grouper. This research highlights the promise of tailored probiotic applications in improving aquaculture practices. Such advancements contribute to more sustainable and efficient fish farming methods.

Microbial community succession and its correlation with the dynamics of flavor compound profiles in naturally fermented stinky sufu

Wuhan stinky sufu is a traditional fermented soybean product with a short ripening period and unique flavor. The aim of this study was to explore the characteristic flavor compounds and core functional microbiota of naturally fermented Wuhan stinky sufu. The results indicated that 11 volatile compounds including guaiacol, 2-pentylfuran, dimethyl trisulfide, dimethyl disulfide, acetoin, 1-octen-3-ol, (2E)-2-nonenal, indole, propyl 2-methylbutyrate, ethyl 4-methylvalerate, nonanal were characteristic aroma compounds, and 6 free amino acids (Ser, Lys, Arg, Glu, Met and Pro) were identified as taste-contributing compounds. 4 fungal genera (Kodamaea, unclassified_Dipodascaceae, Geotrichum, Trichosporon), and 9 bacterial genera (Lysinibacillus, Enterococcus, Acidipropionibacterium, Bifidobacterium, Corynebacterium, Lactococcus, Pseudomonas, Enterobacter, and Acinetobacter) were identified as the core functional microbiota with positive effects on the production of flavor compounds. These findings would enhance the understanding of core flavor-producing microorganisms in naturally fermented soybean products and potentially provide guidance for enhancing the quality of sufu.

Microbial community evolution and functional trade-offs of biofilm in odor treatment biofilters

Biofilters inoculated with activated sludge are widely used for odor control in WWTP. In this process, biofilm community evolution plays an important role in the function of reactor and is closely related to reactor performance. However, the trade-offs in biofilm community and bioreactor function during the operation are still unclear. Herein, an artificially constructed biofilter for odorous gas treatment was operated for 105 days to study the trade-offs in the biofilm community and function. Biofilm colonization was found to drive community evolution during the start-up phase (phase 1, days 0-25). Although the removal efficiency of the biofilter was unsatisfactory at this phase, the microbial genera related to quorum sensing and extracellular polymeric substance secretion led to the rapid accumulation of the biofilm (2.3 kg biomass/m³ filter bed /day). During the stable operation phase (phase 2, days 26-80), genera related to target-pollutant degradation showed increases in relative abundance, which accompanied a high removal efficiency and a stable accumulation of biofilm (1.1 kg biomass/m³ filter bed/day). At the clogging phase (phase 3, days 81-105), a sharp decline in the biofilm accumulation rate (0.5 kg biomass/m³ filter bed /day) and fluctuating removal efficiency were observed. The quorum quenching-related genera and quenching genes of signal molecules increased, and competition for resources among species drove the evolution of the community in this phase. The results of this study highlight the trade-offs in biofilm community and functions during the operation of bioreactors, which could help improve bioreactor performance from a biofilm community perspective.

Bacillus subtilis KM0 Impacts gut Microbiota Profile and Transcription of Genes Related to Transcellular Transport in Zebrafish (Danio rerio)

It is known that probiotic microorganisms play important roles in the composition of the intestinal microbiota. Also, probiotics can affect the paracellular and transcellular transport mechanisms performed by intestinal cells. The aim of this work was to evaluate the effect of the potential probiotic Bacillus subtilis KM0 on the profile of the gut microbiota and transcription of genes related to intestinal transport of zebrafish (Danio rerio). Zebrafish was exposed by immersion to B. subtilis KM0 for 48 h, and the intestines were collected for metataxonomic analysis and transcription of genes related to transcellular and paracellular transports. Although exposure to B. subtilis changed the intestinal microbiota profile of zebrafish, the diversity indices were not altered. A decrease in the number of genera of potentially pathogenic bacteria (Flavobacterium, Plesiomonas, and Pseudomonas) and downregulation in transcription of transcellular transport genes (cubn and amn) were observed. B. subtilis KM0 strain had the expected probiotic effect, by interfering with the proliferation of potentially pathogenic bacteria and decreasing the transcription of genes codifying for signals involved with a mechanism that can be used for invasion by pathogens. The present study demonstrated that, even with a short-term exposure, a bacterium with probiotic potential such as the KM0 strain of B. subtilis can modify the profile of the host's intestinal microbiota, with an impact on the regulation of intestinal genes related to mechanisms that can be used for invasion by pathogenic bacteria.

The Adhesion and Spoilage of Shewanella putrefaciens in Tilapia

Shewanella putrefaciens is a typical spoilage bacteria organism in seafood. The adhesion ability of three S. putrefaciens strains (HR-15, JR-18, HC-71) isolated from putrefied tilapia were evaluated by mucus adhesion in vitro and intestinal adhesion in vivo. The results of the spoilage of the inoculated fish fillets and spoilage of the refrigerated fish both showed that the adhesion ability of S. putrefaciens was positively correlated with the spoilage ability. High-throughput sequencing and GC-MS results showed that S. putrefaciens with high adhesion ability also significantly changed the intestinal flora of fish, causing an increase in the intestinal bacteria such as Plesionomas, Macellibacteroides, Acinetobacter, and Legionella, which then led to the increase in volatile substances such as low-grade aldehydes, alcohols, and ketones in the fish, serious fatty acid oxidation, and excitement of the fishy smell.