Lactic acid bacteria from fresh fruit and vegetables as biocontrol agents of phytopathogenic bacteria and fungi

Evaluation of Antifungal Metabolites Produced by Lactic Acid Bacteria

This study aimed to select and characterize lactic acid bacteria (LAB) with potential antifungal activities against the filamentous fungi Alternaria alternata ATCC MYA-4642, Aspergillus flavus KACC 45470, Aspergillus niger KACC 42589, Cladosporium sphaerospermum ATCC MYA-4645, Penicillium chrysogenum ATCC MYA-4644, and Penicillium expansum KACC 40815. Initial screening of the antifungal activity has identified six LAB strains belonging to the genera Enterococcus and Leuconostoc, selected by their antagonistic activities against at least three of the filamentous fungi in the test panel. Preliminary prediction of bioactive compounds was carried out to narrow down the possible identity of the antagonistic metabolites produced by the studied LAB. Furthermore, metabolic profiles were assessed and used as a basis for the identification of key metabolites based on VIP scores and PCA plot scores. Key metabolites were identified to be β-phenyllactic acid, ⍺-hydroxyisobutyric acid, 1,3-butanediol, phenethylamine, and benzoic acid. Individual assessment of each metabolic compound against the test panel showed specificity inhibitory patterns; yet, combinations between them only showed additive, but not synergetic effects. The pH neutralization significantly reduced the antifungal activity of the cell-free supernatant (CFS), but no bioactive compounds were found to be stable in high temperatures and pressure. This study will be beneficial as an additional building block on the existing knowledge and future antifungal application of LAB produced metabolites. Furthermore, this study also provides a new bio-preservative perspective on unexplored antifungal metabolites produced by LAB as biocontrol agents.

The potential of lactic acid bacteria in mediating the control of plant diseases and plant growth stimulation in crop production - A mini review

The microbial diseases cause significant damage in agriculture, resulting in major yield and quality losses. To control microbiological damage and promote plant growth, a number of chemical control agents such as pesticides, herbicides, and insecticides are available. However, the rising prevalence of chemical control agents has led to unintended consequences for agricultural quality, environmental devastation, and human health. Chemical agents are not naturally broken down by microbes and can be found in the soil and environment long after natural decomposition has occurred. As an alternative to chemical agents, biocontrol agents are employed to manage phytopathogens. Interest in lactic acid bacteria (LAB) research as another class of potentially useful bacteria against phytopathogens has increased in recent years. Due to the high level of biosafety, they possess and the processes they employ to stimulate plant growth, LAB is increasingly being recognized as a viable option. This paper will review the available information on the antagonistic and plant-promoting capabilities of LAB and its mechanisms of action as well as its limitation as BCA. This review aimed at underlining the benefits and inputs from LAB as potential alternatives to chemical usage in sustaining crop productivity.

Lactic Acid Bacteria in the Management of Oily Spot Disease of Pomegranate

The bacterial pathogen of oily spot disease, a major threat to pomegranate growers, was isolated from infected plant parts of pomegranate collected from orchards in Maharashtra, India. The pathogen was identified as Xanthomonas axonopodis pv. punicae (Xap) following phenotypic and molecular characterization by 16S rRNA gene sequencing. It produced pectinase, cellulase, xylanase in medium and in experimentally inoculated tissues with pathogen where pectinase activity was maximum (32.2 U/g). Pearson correlation analysis showed a perfect positive correlation (P < 0.05) between enzyme activity and disease rating scale. This indicates the co-synthesis of hydrolytic enzymes that aid in tissue degradation and suggests their role as virulence factors. Out of 150 indigenously isolated lactic acid bacteria (LAB), Lactococcus lactis subsp. cremoris PB6, Lactobacillus brevis PFR77 and L. lactis subsp. cremoris PFL9, the potent antagonists of Xap, were used in the management of bacterial blight. Under laboratory conditions, cell formulation of PB6, PFR77 and PFL9 were equally effective (P > 0.05) and significantly (P < 0.05) reduced the infection in fruits. Under field conditions, the disease severity index for the treatments where plants received a spray of PB6 with streptocycline, was lowest (4.61%) as compared to cells (15.74%), culture supernatant (20.66%) and their integrated treatments (21.38%), and streptocycline (15.37%) treatments. However, no significant difference (P > 0.05) was noticed between cells and streptocycline treatments, thus, indicating the effectiveness of LAB in treating bacterial blight. This is the first report on the use of antagonistic LAB for the control of oily spot disease of pomegranate.

Comparison of the Peel-Associated Epiphytic Bacteria of Anthocyanin-Rich "Sun Black" and Wild-Type Tomatoes under Organic and Conventional Farming

Tomatoes are among the most consumed vegetables worldwide and represent a source of health-beneficial substances. Our study represents the first investigating the peel-associated epiphytic bacteria of red and purple (anthocyanin-rich) tomatoes subjected to organic and conventional farming systems. Proteobacteria was the dominant phylum (relative abundances 79-91%) in all experimental conditions. Enterobacteriaceae represented a large fraction (39.3-47.5%) of the communities, with Buttiauxella and Atlantibacter as the most represented genera. The core microbiota was composed of 59 operational taxonomic units (OTUs), including the majority of the most abundant ones. The occurrence of the most abundant OTUs differed among the experimental conditions. OTU 1 (Buttiauxella), OTU 2 (Enterobacteriales), and OTU 6 (Bacillales) were higher in red and purple tomatoes grown under organic farming. OTU 5 (Acinetobacter) had the highest abundance in red tomatoes subjected to organic farming. OTU 3 (Atlantibacter) was among the major OTUs in red tomatoes under both farming conditions. OTU 7 (Clavibacter) and OTU 8 (Enterobacteriaceae) had abundances ≥1% only in red tomatoes grown under conventional farming. PCA and clustering analysis highlighted a high similarity between the bacterial communities of red and purple tomatoes grown under organic farming. Furthermore, the bacterial communities of purple tomatoes grown under organic farming showed the lowest diversity and evenness. This work paves the way to understand the role of nutritional superior tomato genotypes, combined with organic farming, to modulate the presence of beneficial/harmful bacteria and supply healthier foods within a sustainable agriculture.

Antimicrobial activity and safety features assessment of Weissella spp. from environmental sources

Weissella strains have been reported to be useful in biotechnological and probiotic determinations, and some of them are considered opportunistic pathogens. Given the widespread interest about antimicrobial susceptibilities, transmission of resistances, and virulence factors, there is little research available on such topics for Weissella. The aim of this study was to assess the safety aspects and antimicrobial potential of 54 Weissella spp. strains from different environmental sources. Antibiotic susceptibility, hemolytic activity, horizontal transfer, and antibacterial activity were studied, as well as the detection of biogenic amine BA production on decarboxylase medium and PCR was performed. All the strains were nonhemolytic and sensitive to chloramphenicol and ampicillin. Several strains were classified as resistant to fusidic acid, and very low resistance rates were detected to ciprofloxacin, tetracycline, streptomycin, lincomycin, erythromycin, and rifampicin, although all strains had intrinsic resistance to vancomycin, nalidixic acid, kanamycin, and teicoplanin. Two BA-producing strains (W. halotolerans FAS30 and FAS29) exhibited tyrosine decarboxylase activity, and just one W. confusa FS077 produced both tyramine and histamine, and their genetic determinants were identified. Ornithine decarboxylase/odc gene was found in 16 of the Weissella strains, although 3 of them synthesize putrescine. Interestingly, eight strains with good properties displayed antibacterial activity. Conjugation frequencies of erythromycin from Bacillus to Weissella spp. varied in the average of 3 × 10-9 transconjugants/recipient. However, no tetracycline-resistant transconjugant was obtained with Enterococcus faecalis JH2-2 as recipient. The obtained results support the safe status of Weissella strains, derived from environmental sources, when used as probiotics in animal feed.

Root-Knot Nematode (Meloidogyne incognita) Control Using a Combination of Lactiplantibacillus plantarum WiKim0090 and Copper Sulfate

Lactic acid bacteria (LAB) exert antagonistic activity against root-knot nematodes, mainly by producing organic acids via carbohydrate fermentation. However, they have not yet been used for root-knot nematode (Meloidogyne incognita) control owing to a lack of economic feasibility and effectiveness. In this study, we aimed to isolate organic acid-producing LAB from kimchi (Korean traditional fermented cabbage) and evaluated their nematicidal activity. Among the 234 strains isolated, those showing the highest nematicidal activity were selected and identified as Lactiplantibacillus plantarum WiKim0090. Nematicidal activity and egg hatch inhibitory activity of WiKim0090 culture filtrate were dose dependent. Nematode mortality 3 days after treatment with 2.5% of the culture filtrate was 100%, with a 50% lethal concentration of 1.41%. In pot tests, the inhibitory activity of an L. plantarum WiKim0090-copper sulfate mixture on gall formation increased. Compared to abamectin application, which is a commercial nematicide, a higher control value was observed using the WiKim0090-copper sulfate mixture, indicating that this combination can be effective in controlling the root-knot nematode.

Effect of fermentation of chosen vegetables on the nutrient, mineral, and biocomponent profile in human and animal nutrition

In the present study, the dry matter, crude ash, crude protein, ether extract, and energy, macro- (Na, K, Ca, Mg, P), micro- (Zn, Cu, Fe) minerals, heavy metals (Pb, Cd), vitamin C, A, carotene, and phenolic content were determined in chosen raw and fermented vegetables. The dietary intake of several macro- and microconstituents per one serving (100 g or humans and animals: ducks and pigs) was calculated. The fermentation process was found to reduce water and increase fat content in the vegetables. Lower levels of vitamin C and phenols were also found in the fermented vegetables. The vitamin A and carotene content in the fermented carrots and peppers were increased in comparison with the raw vegetables. The fermentation process decreased the concentration of some basic nutrients, mineral content, vitamins C and A, and phenols. Broccoli, peppers, and red beet had the highest levels of the analyzed nutrients and bioconstituents. The fermentation process is regarded by nutritionists as beneficial to human health. The addition of fermented plants is recommended in animal nutrition as well. This process modifies the chemical composition of preserved vegetables, e.g. it reduces the concentration of dietary fiber, and brings favorable effects in poultry and pig nutrition.

Community Structure of Phyllosphere Bacteria in Different Cultivars of Fingered Citron (Citrus medica 'Fingered') and Their Correlations With Fragrance

In recent years, plant metabolomics and microbiome studies have suggested that the synthesis and secretion of plant secondary metabolites are affected by microbial-host symbiotic interactions. In this study, six varieties of fingered citron (Citrus medica 'Fingered') are sampled to study their phyllosphere bacterial communities and volatile organic compounds (VOCs). High-throughput sequencing is used to sequence the V5-V7 region of the 16S rRNA of the fingered citron phyllosphere bacteria, and the results showed that Proteobacteria, Actinobacteria, Firmicutes, and Bacteroidetes were the dominant bacterial phylum in the phyllosphere of fingered citron. There were significant differences in the phyllosphere bacteria community between XiuZhen and the remaining five varieties. The relative abundance of Actinomycetospora was highest in XiuZhen, and Halomonas, Methylobacterium, Nocardioides, and Pseudokineococcus were also dominant. Among the remaining varieties, Halomonas was the genus with the highest relative abundance, while the relative abundances of all the other genera were low. Headspace solid-phase microextraction (HS-SPME) and gas chromatography-mass spectrometry (GC-MS) were used to analyze and identify the aroma compounds of six different fingered citron, and a total of 76 aroma compounds were detected in six varieties. Pinene, geraniol, and linalool were found to be the primary VOCs that affect the aroma of fingered citron based on relative odor activity value. The correlation analysis showed 55 positive and 60 negative correlations between the phyllosphere bacterial flora and aroma compounds of fingered citron. The top 10 genera in the relative abundance were all significantly associated with aroma compounds. This study provides deep insight into the relation between bacteria and VOCs of fingered citron, and this may better explain the complexity of the analysis of bacterial and metabolic interactions.

Characterization of antimicrobial compounds obtained from the potential probiotic Lactiplantibacillus plantarum S61 and their application as a biopreservative agent

This work aimed to characterize the antimicrobial compounds obtained from the potential probiotic Lactiplantibacillus plantarum S61, isolated from traditional fermented green olive, involved in their activity against fungi and bacteria responsible for food spoilage and poisonings. Their application as a biopreservative agent was also investigated. The culture of L. plantarum S61 showed substantial antifungal and antibacterial activity against yeasts (Rhodotorula glutinis and Candida pelliculosa), molds (Penicillium digitatum, Aspergillus niger, Fusarium oxysporum, and Rhizopus oryzae), and pathogenic bacteria (Listeria monocytogenes ATCC 19,117, Salmonella enterica subsp. enterica ATCC 14,028, Staphylococcus aureus subsp. aureus ATCC 6538, Pseudomonas aeruginosa ATCC 49,189), with inhibition zones > 10 mm. Likewise, the cell-free supernatant (CFS) of L. plantarum S61 showed an essential inhibitory effect against fungi and bacteria, with inhibition diameters of 12.25-22.05 mm and 16.95-17.25 mm, respectively. The CFS inhibited molds' biomass and mycelium growth, with inhibition ranges of 63.18-83.64% and 22.57-38.93%, respectively. The antifungal activity of the CFS was stable during 4 weeks of storage at 25 °C, while it gradually decreased during storage at 4 °C. Several antimicrobial compounds were evidenced in the CFS of L. plantarum S61, including organic acids, ethanol, hydrogen peroxide, diacetyl, proteins, and fatty acids. The protein fraction, purified by reversed-phase high-performance liquid chromatography (RP-HPLC), demonstrated important antifungal activity, in relation to the fraction with molecular weight between 2 and 6 kDa. L. plantarum S61 and its CFS, tested in apple and orange fruit biopreservation, demonstrated their protective effect against P. digitatum spoilage. The CFS exhibited effectiveness in reducing Salmonella enterica subsp. enterica ATCC 14,028 in apple juice. L. plantarum S61 and/or its bioactive compounds CFS represent a promising strategy for biocontrol against pathogens and spoilage microorganisms in the agro-industry.

One Health Probiotics as Biocontrol Agents: One Health Tomato Probiotics

Tomato (Lycopersicon esculentum) is one of the most popular and valuable vegetables in the world. The most common products of its industrial processing in the food industry are juice, tomato paste, various sauces, canned or sun-dried fruits and powdered products. Tomato fruits are susceptible to bacterial diseases, and bacterial contamination can be a risk factor for the safety of processed tomato products. Developments in bioinformatics allow researchers to discuss target probiotic strains from an existing large number of probiotic strains for any link in the soil-plant-animal-human chain. Based on the literature and knowledge on the "One Health" concept, this study relates to the suggestion of a new term for probiotics: "One Health probiotics", beneficial for the unity of people, animals, and the environment. Strains of Lactiplantibacillus plantarum, having an ability to ferment a broad spectrum of plant carbohydrates, probiotic effects in human, and animal health, as well as being found in dairy products, vegetables, sauerkraut, pickles, some cheeses, fermented sausages, fish products, and rhizospheric soil, might be suggested as one of the probable candidates for "One Health" probiotics (also, for "One Health-tomato" probiotics) for the utilization in agriculture, food processing, and healthcare.

The Potential of Fermented Food from Southeast Asia as Biofertiliser

The intensive amount of chemical usage in agricultural practices could contribute to a significant impact on food safety issues and environmental health. Over-usage of chemical fertilisers may alter soil characteristics and contaminate water sources, leading to several human and animal health issues. Recently, there have been efforts to use microbial biofertilisers as a more sustainable and environmentally friendly agricultural practice in the common household of Southeast Asia. Traditionally, this method tends to utilise leftover food materials and readily available bacterial cultures, such as yoghurt drinks, and ferment them under a specific period in either solid or liquid form. So far, most of the testimonial-based feedbacks from local communities have been positive, but only limited information is available in the literature regarding the usage of biofertiliser fermented food (BFF). Previously, raw food waste has been used in the agriculture system to promote plant growth, however, the functional role of fermented food in enhancing plant growth have yet to be discovered. An understanding of the symbiotic relationship between fermented food and plants could be exploited to improve agricultural plant production more sustainably. Fermented food is known to be rich in good microbial flora (especially lactic acid bacteria (LAB)). LAB exist in different sources of fermented food and can act as a plant growth-promoting agent, improving the nutrient availability of food waste and other organic materials. Therefore, in this review, the potential use of seafood-based, plant-based, and animal-based fermented food as biofertiliser, especially from Southeast Asia, will be discussed based on their types and microbial and nutritional contents. The different types of fermented food provide a wide range of microbial flora for the enrichment of proteins, amino acids, vitamins, and minerals content in enhancing plant growth and overall development of the plant. The current advances of biofertiliser and practices of BFF will also be discussed in this review.

Dietary Clostridium butyricum and Bacillus subtilis Promote Goose Growth by Improving Intestinal Structure and Function, Antioxidative Capacity and Microbial Composition

Simple Summary

In this study, the effects of dietary supplementation of Clostridium butyricum and/or Bacillus subtilis were determined on growth performance, intestinal antioxidative capacity, intestinal morphology, cytokine production, and intestinal microbial composition in Yangzhou geese. Data showed that probiotics promoted feed intake and growth, improved antioxidative capacity and intestinal morphology, increased the relative abundances of Firmicutes and Lactobacillus in intestinal content, decreased the relative abundances of Proteobacteria and Ralstonia, and altered α-diversity and the predicted functions of intestinal microflora, but did not induce the expression of genes related to intestinal inflammation and tight junction.

Abstract

Probiotics are a substitute for antibiotics in the sense of intestinal health maintenance. Clostridium butyricum and Bacillus subtilis, as probiotic bacteria, have been widely used in animal production. The aim of this study was to investigate the effects of the two probiotic bacteria in geese. A total of 288 1-day old, healthy Yangzhou geese were randomly assigned into 4 groups (A, B, C and D) with 6 replicates of 12 birds each. Group A, as control, was fed a basal diet, and the treatment groups (B, C and D) were fed the basal diet supplemented with 250 mg/kg Clostridium butyricum (the viable count was 3.0 × 10⁶ CFU/g), 250 mg/kg Bacillus subtilis (the viable count was 2.0 × 10⁷ CFU/g), or a combination of the two probiotic bacteria for 70 days, respectively. The results indicated that: compared with the control group, dietary probiotics (1) promoted the growth and feed intake of the geese, (2) increased the absolute weight of duodenum, (3) increased the antioxidative capacity (total antioxidative capacity (T-AOC), total superoxide dismutase (T-SOD) and glutathione peroxidase (GSH-PX)) of intestinal mucosa, (4) improved intestinal morphology (the ratio of villus height to crypt depth), (5) but did not induce inflammation and changes of tight junction in the intestine, which was indicated by no induction of pro/inflammatory cytokines (IL-1β, IL-6, IL-10, TNFAIP3) and tight junction related genes (TJP1 and OCLN). Moreover, dietary probiotics increased the relative abundances of Firmicutes phylum and Lactobacillus genus and decreased the relative abundances of Proteobacteria phylum or Ralstonia genus in the intestinal content. In addition, the alpha diversity (observed species, Chao1, and estimate the number of OTUs in the community(ACE)) was reduced and the predicted functions of intestinal microflora, including peptidases, carbon fixation and metabolic function of starch and sugar, were enhanced by dietary probiotics. In conclusion, dietary probiotics promote the growth of geese by their positive effects on intestinal structure and function, the composition and functions of gut microflora, and intestinal antioxidative capacity.

Gut Microbiota Dysbiosis Influences Metabolic Homeostasis in Spodoptera frugiperda

Insect gut microbiota plays important roles in acquiring nutrition, preventing pathogens infection, modulating immune responses, and communicating with environment. Gut microbiota can be affected by external factors such as foods and antibiotics. Spodoptera frugiperda (Lepidoptera: Noctuidae) is an important destructive pest of grain crops worldwide. The function of gut microbiota in S. frugiperda remains to be investigated. In this study, we fed S. frugiperda larvae with artificial diet with antibiotic mixture (penicillin, gentamicin, rifampicin, and streptomycin) to perturb gut microbiota, and then examined the effect of gut microbiota dysbiosis on S. frugiperda gene expression by RNA sequencing. Firmicutes, Proteobacteria, Bacteroidetes, and Actinobacteria were the most dominant phyla in S. frugiperda. We found that the composition and diversity of gut bacterial community were changed in S. frugiperda after antibiotics treatment. Firmicutes was decreased, and abundance of Enterococcus and Weissella genera was dramatically reduced. Transcriptome analysis showed that 1,394 differentially expressed transcripts (DETs) were found between the control and antibiotics-treated group. The Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) results showed that antibiotics-induced dysbiosis affected many biological processes, such as energy production, metabolism, and the autophagy–lysosome signal pathway. Our results indicated that dysbiosis of gut microbiota by antibiotics exposure affects energy and metabolic homeostasis in S. frugiperda, which help better understand the role of gut microbiota in insects.

Potential Use of Lactic Acid Bacteria with Pathogen Inhibitory Capacity as a Biopreservative Agent for Chorizo

The biopreservation of meat products is of great interest due to the demand for products with low or minimal chemical additives. Lactic acid bacteria (LAB) have been used as protective cultures for many centuries. The objective of this work was to characterize 10 native LAB isolated from meat masses with biopreservative potential for meat products. The isolates were subjected to viability tests with different concentrations of NaCl, nitrite, and nitrate salts, pHs, and temperature conditions. Antibiotic resistance and type of lactic acid isomer were tested. In addition, the isolates were tested against seven pathogens, and inhibitory substances were identified by diffusion in agar wells. Finally, two isolates, Lb. plantarum (SB17) and Lb. sakei (SB3) were tested as protective cultures of chorizo in a model. As a result, the viability at different concentrations of NaCl and nitrate and nitrate salts were obtained. pH and temperature exerted a negative effect on the growth of some of the isolates. Pathogens were inhibited mainly by the presence of organic acids; P. aurius was the most susceptible, and S. typhimurium and S. marcescens were the most resistant. The strains SB17 and SB3 had similar effects on chorizo, and time exerted a deleterious effect on microbiological quality and pH. The results indicated that the 10 isolates show promising characteristics for the preservation of cooked meat products, with the strain Lb. plantarum (SB17) being the most promising.

Molecular Assay Development to Monitor the Kinetics of Viable Populations of Two Biocontrol Agents, Bacillus subtilis QST 713 and Gliocladium catenulatum J1446, in the Phyllosphere of Lettuce Leaves

Simple Summary

There is a need to be able to track the viable populations of biocontrol agents when applied on the foliar surfaces of plants. We have developed a molecular-based method for the quantification of viable cells of two commercial biocontrol agents—a bacterium (Bacillus subtilis) and a fungus (Gliocladium catenulatum). The method has been tested on the leaf surfaces of lettuce plants to examine the changes in viable population over 10–12 days for the first time.

Abstract

Optimising the use of biocontrol agents (BCAs) requires the temporal tracking of viable populations in the crop phyllosphere to ensure that effective control can be achieved. No sensitive systems for quantifying viable populations of commercially available BCAs, such as Bacillus subtilis and Gliocladium catenulatum, in the phyllosphere of crop plants are available. The objective of this study was to develop a method to quantify viable populations of these two BCAs in the crop phyllosphere. A molecular tool based on propidium monoazide (PMA) (PMAxx™-qPCR) capable of quantifying viable populations of these two BCAs was developed. Samples were treated with PMAxx™ (12.5–100 μM), followed by 15 min incubation, exposure to a 800 W halogen light for 30 min, DNA extraction, and quantification using qPCR. This provided a platform for using the PMAxx™-qPCR technique for both BCAs to differentiate viable from dead cells. The maximum number of dead cells blocked, based on the DNA, was 3.44 log₁₀ for B. subtilis and 5.75 log₁₀ for G. catenulatum. Validation studies showed that this allowed accurate quantification of viable cells. This method provided effective quantification of the temporal changes in viable populations of the BCAs in commercial formulations on lettuce leaves in polytunnel and glasshouse production systems.

Antagonistic Activity of Lactic Acid Bacteria Against Phytopathogenic Fungi Isolated from Cherry Tomato (Solanum lycopersicum var. cerasiforme)

The postharvest deterioration of cherry tomatoes due to diseases caused by fungi is one of the main causes of the loss of this product. The objective of this study was to determine the antagonistic capacity by evaluating the antifungal power of nine strains of lactic acid bacteria (LAB) in vitro against the phytopathogenic fungi Aspergillus niger, Fusarium sp., and Rhizopus stolonifer isolated from cherry tomatoes (Solanum lycopersicum var. cerasiforme) and to measure the biosurfactant production capacity, its antagonism in vivo, and the production of organic acids. The results showed that seven of the nine strains were able to inhibit at least one of the three fungi isolated in the in vitro assay. In eight of nine strains, biosurfactant production was identified, and the strains Weissella confusa and Lactiplantibacillus plantarum A6 showed the highest antifungal activity in vitro and in vivo against the fungi evaluated, with the identification of organic acid production in both strains. LAB demonstrated the ability to inhibit cherry tomato fungi, thus emerging as an alternative to the use of chemical preservatives in the production of this fruit and being projected as a preservation technology for this type of product through the use of strains or their metabolites.

Effects of Lacto-Fermented Agricultural By-Products as a Natural Disinfectant against Post-Harvest Diseases of Mango (Mangifera indica L.)

Background: the antagonism activity of lactic acid bacteria metabolites has the potential to prevent fungal growth on mango. Methods: the potential of developing natural disinfectant while using watermelon rinds (WR), pineapple (PP), orange peels (OP), palm kernel cake (PKC), and rice bran (RB), via lacto-fermentation was investigated. The obtained lactic acid bacteria (LAB) metabolites were then employed and the in vitro antifungal activity toward five spoilage fungi of mango was tested through liquid and solid systems. Besides, the effect of the produced disinfectant on the fungal growth inhibition and quality of mango was investigated. Results: the strains Lactobacillus plantarum ATCC8014 and Lactobacillus fermentum ATCC9338 growing in the substrates PKC and PP exhibited significantly higher in vitro antifungal activity against Colletotrichum gloeosporioides and Botryodiplodia theobromae as compared to other tested LAB strains and substrates. The in-situ results demonstrated that mango samples that were treated with the disinfectant produced from PKC fermented with L. plantarum and L. fermentum had the lowest disease incidence and disease severity index after 16 days shelf life, as well as the lowest conidial concentration. Furthermore, PKC that was fermented by L. fermentum highly maintained the quality of the mango. Conclusions: lactic acid fermentation of PKC by L. fermentum demonstrated a high potential for use as a natural disinfectant to control C. gloeosporioides and B. theobromae on mango.

Pectobacterium brasiliense: Genomics, Host Range and Disease Management

Pectobacterium brasiliense (Pbr) is considered as one of the most virulent species among the Pectobacteriaceae. This species has a broad host range within horticulture crops and is well distributed elsewhere. It has been found to be pathogenic not only in the field causing blackleg and soft rot of potato, but it is also transmitted via storage causing soft rot of other vegetables. Genomic analysis and other cost-effective molecular detection methods such as a quantitative polymerase chain reaction (qPCR) are essential to investigate the ecology and pathogenesis of the Pbr. The lack of fast, field deployable point-of-care testing (POCT) methods, specific control strategies and current limited genomic knowledge make management of this species difficult. Thus far, no comprehensive review exists about Pbr, however there is an intense need to research the biology, detection, pathogenicity and management of Pbr, not only because of its fast distribution across Europe and other countries but also due to its increased survival to various climatic conditions. This review outlines the information available in peer-reviewed literature regarding host range, detection methods, genomics, geographical distribution, nomenclature and taxonomical evolution along with some of the possible management and control strategies. In summary, the conclusions and a further directions highlight the management of this species.

A microbial ecosystem: agricultural Jiaosu achieves effective and lasting antifungal activity against Botrytis cinerea

Synthetic fungicides are eco-unfriendly to agriculture and the environment. Agricultural Jiaosu (AJ), which originates from organic wastes, has the potential to be a substitute for synthetic fungicides. In this study, the characteristics of AJ and its antifungal activity against Botrytis cinerea were investigated for the first time. AJ was rich in lactic acid (4.46 g/L), acetic acid (1.52 g/L), Lactobacillus (72.45%) and Acetobacter (15.23%), which was a microbial ecosystem consisting of acid-based substances (AS) and beneficial microorganisms (BM). The results of the antifungal assays suggested that B. cinerea was effectively inhibited by AJ, with the half-maximal inhibitory concentration (IC₅₀) of 9.24%. AJ showed the strongest and most-lasting inhibitory effect compared to cell-free supernatant and microbial solution of AJ, indicating that AS and BM and their synergistic effect contributed to the antifungal activity of AJ. Two-step inhibition’ is an antifungal mode of AJ. Firstly, AS not only inhibited the pathogen directly but also provided a dominant niche for BM of AJ. Then, BM in AJ, especially Acetobacter, proliferated and metabolized acetic acid continuously. Thus, AJ achieved high-efficiency and long-acting inhibition. AJ is a promising biological agent considering its features of an eco-friendly, low-cost and easy-to-operate biological agent in rural areas.

Isolation and Characterization of Biosurfactant-Producing Bacteria From Oil Well Batteries With Antimicrobial Activities Against Food-Borne and Plant Pathogens

Microbial biosurfactants, produced by fungi, yeast, and bacteria, are surface-active compounds with emulsifying properties that have a number of known activities, including the solubilization of microbial biofilms. In an on-going survey to uncover new or enhanced antimicrobial metabolite-producing microbes from harsh environments, such as oil-rich niches, 123 bacterial strains were isolated from three oil batteries in the region of Chauvin, Alberta, and characterized by 16S rRNA gene sequencing. Based on their nucleotide sequences, the strains are associated with 3 phyla (Actinobacteria, Proteobacteria and Firmicutes), as well as 17 other discrete genera that shared high homology with known sequences, with the majority of these strains identified to the species level. The most prevalent strains associated with the three oil wells belonged to the Bacillus genus. Thirty-four of the 123 strains were identified as biosurfactant-producers, among which Bacillus methylotrophicus strain OB9 exhibited the highest biosurfactant activity based on multiple screening methods and a comparative analysis with the commercially available biosurfactant, Tween 20. B. methylotrophicus OB9 was selected for further antimicrobial analysis and addition of live cultures of B. methylotrophicus OB9 (or partially purified biosurfactant fractions thereof) were highly effective on biofilm disruption in agar diffusion assays against several Gram-negative food-borne bacteria and plant pathogens. Upon co-culturing with B. methylotrophicus OB9, the number of either Salmonella enterica subsp. enterica Newport SL1 or Xanthomonas campestris B07.007 cells significantly decreased after 6 h and were not retrieved from co-cultures following 12 h exposure. These results also translated to studies on plants, where bacterized tomato seedlings with OB9 significantly protected the tomato leaves from Salmonella enterica Newport SL1 contamination, as evidenced by a 40% reduction of log10 CFU of Salmonella/mg leaf tissue compared to non-bacterized tomato leaves. When B. methylotrophicus 0B9 was used for bacterized lettuce, the growth of X. campestris B07.007, the causal agent of bacterial leaf spot of lettuce, was completely inhibited. While limited, these studies are noteworthy as they demonstrate the inhibition spectrum of B. methylotrophicus 0B9 against both human and plant pathogens; thereby making this bacterium attractive for agricultural and food safety applications in a climate where microbial-biofilm persistence is an increasing problem.

Seasonal epiphytic microbial dynamics on grapevine leaves under biocontrol and copper fungicide treatments

Winemakers have long used copper as a conventional fungicide treatment on grapevine and only recently, the use of biocontrol agents depicted a promising alternative. Most of the studies that investigate the impact of fungicide treatments, focus on specific pathogenic microbes. In the present work instead, a field experiment conducted in South Africa shows the seasonal microbial change occurring on grapevine leaves, periodically treated with two different fungicide treatments: copper sulphate and Lactobacillus plantarum MW-1. In this work, NGS data were combined with strain-specific and community qPCRs to reveal the shift of the microbial communities throughout the growing season and highlight the impact of fungicides on the microbiota. Only the family of Lactobacillaceae systematically changed between treatments, while the bacterial community remained relatively stable over time. MW-1 was exclusively detected on biocontrol-sprayed leaves. Conversely, the fungal community was largely shaped by sampling time, underlining the succession of different dominant taxa over the months. Between treatments, only a few fungal taxa appeared to change significantly and the fungal load was also comparable. Monitoring the dynamics of the microbial community under different fungicide treatments may advise the best timing to apply treatments to the plants, toward the realization of more sustainable agricultural practices.

Biological control of Erwinia mallotivora, the causal agent of papaya dieback disease by indigenous seed-borne endophytic lactic acid bacteria consortium

Dieback disease caused by Erwinia mallotivora is a major threat to papaya plantation in Malaysia. The current study was conducted to evaluate the potential of endophytic lactic acid bacteria (LAB) isolated from papaya seeds for disease suppression of papaya dieback. Two hundred and thirty isolates were screened against E. mallotivora BT-MARDI, and the inhibitory activity of the isolates against the pathogen was ranging from 11.7–23.7 mm inhibition zones. The synergistic experiments revealed that combination of W. cibaria PPKSD19 and Lactococcus lactis subsp. lactis PPSSD39 increased antibacterial activity against the pathogen. The antibacterial activity was partially due to the production of bacteriocin-like inhibitory substances (BLIS). The nursery experiment confirmed that the application of bacterial consortium W. cibaria PPKSD19 and L. lactis subsp. lactis PPSSD39 significantly reduced disease severity to 19% and increased biocontrol efficacy to 69% of infected papaya plants after 18 days of treatment. This study showed that W. cibaria PPKSD19 and L. lactis subsp. lactis PPSSD39 are potential candidate as biocontrol agents against papaya dieback disease.

Role of biological control agents and physical treatments in maintaining the quality of fresh and minimally-processed fruit and vegetables

Fruit and vegetables are an important part of human diets and provide multiple health benefits. However, due to the short shelf-life of fresh and minimally-processed fruit and vegetables, significant losses occur throughout the food distribution chain. Shelf-life extension requires preserving both the quality and safety of food products. The quality of fruit and vegetables, either fresh or fresh-cut, depends on many factors and can be determined by analytical or sensory evaluation methods. Among the various technologies used to maintain the quality and increase shelf-life of fresh and minimally-processed fruit and vegetables, biological control is a promising approach. Biological control refers to postharvest control of pathogens using microbial cultures. With respect to application of biological control for increasing the shelf-life of food, the term biopreservation is favored, although the approach is identical. The methods for screening and development of biocontrol agents differ greatly according to their intended application, but the efficacy of all current approaches following scale-up to commercial conditions is recognized as insufficient. The combination of biological and physical methods to maintain quality has the potential to overcome the limitations of current approaches. This review compares biocontrol and biopreservation approaches, alone and in combination with physical methods. The recent increase in the use of meta-omics approaches and other innovative technologies, has led to the emergence of new strategies to increase the shelf-life of fruit and vegetables, which are also discussed herein.

Deciphering the microbiome shift during fermentation of medicinal plants

The importance of the human-microbiome relationship for positive health outcomes has become more apparent over the last decade. Influencing the gut microbiome via modification of diet represents a possibility of maintaining a healthy gut flora. Fermented food and lactic acid bacteria (LAB) display a preventive way to inhibit microbial dysbioses and diseases, but their ecology on plants is poorly understood. We characterized the microbiome of medicinal plants (Matricaria chamomilla L. and Calendula officinalis L.) using 16S rRNA gene profiling from leaves that were fermented over a six-week time course. The unfermented samples were characterized by a distinct phyllosphere microbiome, while the endosphere revealed a high similarity. During fermentation, significant microbial shifts were observed, whereby LAB were enhanced in all approaches but never numerically dominated. Among the LAB, Enterococcaceae were identified as the most dominant family in both plants. M. chamomilla community had higher relative abundances of Lactobacillaceae and Carnobacteriaceae, while C. officinalis showed a higher presence of Leuconostocaceae and Streptococcaceae. The natural leaf microbiome and the indigenous LAB communities of field-grown Asteraceae medicinal plants are plant-specific and habitat-specific and are subjected to significant shifts during fermentation. Leaf surfaces as well as leaf endospheres were identified as sources for biopreservative LAB.

Diversity and Functional Properties of Lactic Acid Bacteria Isolated From Wild Fruits and Flowers Present in Northern Argentina

Lactic acid bacteria (LAB) are capable of converting carbohydrate substrates into organic acids (mainly lactic acid) and producing a wide range of metabolites. Due to their interesting beneficial properties, LAB are widely used as starter cultures, as probiotics, and as microbial cell factories. Exploring LAB present in unknown niches may lead to the isolation of unique species or strains with relevant technological properties. Autochthonous rather than allochthonous starter cultures are preferred in the current industry of fermented food products, due to better adaptation and performance of autochthonous strains to the matrix they originate from. In this work, the lactic microbiota of eight different wild tropical types of fruits and four types of flowers were studied. The ability of the isolated strains to produce metabolites of interest to the food industry was evaluated. The presence of 21 species belonging to the genera Enterococcus, Fructobacillus, Lactobacillus, Lactococcus, Leuconostoc, and Weissella was evidenced by using culture-dependent techniques. The isolated LAB corresponded to 95 genotypically differentiated strains by applying rep-PCR and sequencing of the 16S rRNA gene; subsequently, representative strains of the different isolated species were studied for technological properties, such as fast growth rate and acidifying capacity; pectinolytic and cinnamoyl esterase activities, and absence of biogenic amine biosynthesis. Additionally, the strains' capacity to produce ethyl esters as well as mannitol was evaluated. The isolated fruit- and flower-origin LAB displayed functional properties that validate their potential use in the manufacture of fermented fruit-based products setting the background for the design of novel functional foods.

Recent advances in the biocontrol of Xanthomonas spp

Bacterial diseases caused by members of the genus Xanthomonas affect agricultural crops of great importance in the world. At least 350 different plant diseases are caused by species of Xanthomonas. Important crops, such as: rice, citrus, cassava, tomato, sugar cane, passionfruit and brassicas are severely affected by bacteria of this genus. Due to its rapid propagation, handling difficulties, problems with chemical control and severity of the losses of the affected plantations Xanthomonas is a difficult obstacle for agriculture around the world. In addition, chemical control of some of these diseases is carried out using copper-based chemicals, which causes a negative impact on health and the environment. A more sustainable alternative to combat these diseases is the control of Xanthomonas by microorganisms directly or indirectly through the use of its secondary metabolites involved in biocontrol. This review is a report concerning the recent advances in the search for microorganisms for the biocontrol of several Xanthomonas that are important for the world economy.

Nutritional and Microbiological Quality of Tiger Nut Tubers (Cyperus esculentus), Derived Plant-Based and Lactic Fermented Beverages

Tiger nut (Cyperus esculentus) is a tuber that can be consumed raw or processed into beverages. Its nutritional composition shows a high content of lipid and dietary fiber, close to those of nuts, and a high content of starch, like in other tubers. Tiger nuts also contain high levels of phosphorus, calcium, and phenolic compounds, which contribute to their antioxidant activity. From those characteristics, tiger nuts and derived beverages are particularly relevant to limit food insecurity in regions where the plant can grow. In Europe and United States, the tiger nut derived beverages are of high interest as alternatives to milk and for gluten-free diets. Fermentation or addition of probiotic cultures to tiger nut beverages has proven the ability of lactic acid bacteria to acidify the beverages. Preliminary sensory assays concluded that acceptable products are obtained. In the absence of pasteurization, the safety of tiger nut-based beverages is not warranted. In spite of fermentation, some foodborne pathogens or mycotoxigenic fungi have been observed in fermented beverages. Further studies are required to select a tailored bacterial cocktail which would effectively dominate endogenous flora, preserve bioactive compounds and result in a well-accepted beverage.

Lactobacillus plantarum 299V improves the microbiological quality of legume sprouts and effectively survives in these carriers during cold storage and in vitro digestion

Probiotics improve consumers' health and additionally may positively influence the microbiological and organoleptic quality of food. In the study, legume sprouts were inoculated with Lactobacilllus plantarum 299V to produce a new functional product ensuring the growth and survival of the probiotic and high microbiological quality of the final product. Legume sprouts, which are an excellent source of nutrients, were proposed as alternative carriers for the probiotic. The key factors influencing the production of probiotic-rich sprouts include the temperature (25°C) of sprouting and methods of inoculation (soaking seeds in a suspension of probiotics). Compared to the control sprouts, the sprouts enriched with the probiotic were characterized by lower mesophilic bacterial counts. In the case of fresh and stored probiotic-rich sprouts, lactic acid bacteria (LAB) accounted for a majority of total microorganisms. The Lb. plantarum population was also stable during the cold storage. The high count of LAB observed in the digest confirmed the fact that the studied sprouts are effective carriers for probiotics and ensure their survival in the harmful conditions of the digestive tract in an in vitro model. Enrichment of legume sprouts with probiotics is a successful attempt and yields products for a new branch of functional foods.

Application of Autochthonous Lactobacillus Strains as Biopreservatives to Control Fungal Spoilage in Caciotta Cheese

Fungal spoilage is one of the main causes of economic losses worldwide in the food industry. In the last years, consumer's demands for preservative-free processed foods have increased as a result of growing awareness about the health hazards associated with chemicals. Lactic acid bacteria have been extensively studied for their antibacterial and antifungal potential in order to be used as biopreservatives. The first objective of this study was to investigate in vitro the antifungal activity of autochthonous Lactobacillus strains against moulds commonly associated with cheese spoilage. Then, the Lactobacillus strains with the highest inhibitory effect and broadest spectrum were tested in single or mixed cultures against Penicillium chrysogenum ATCC 9179 and Aspergillus flavus ATCC 46283 on miniature Caciotta cheese produced at laboratory scale to evaluate in situ their ability to prevent mould growth and to determine their impact on cheese organoleptic properties and starter culture activity. The growth of the starter lactococcal population exhibited similar trend and values during ripening, suggesting that the addition of lactobacilli did not influence its growth and survival. Inhibition of P. chrysogenum inoculated in the milk was determined in cheeses produced with single or mixed Lactobacillus adjuncts as compared to cheeses without adjunct. The mixed adjunct cultures resulted in more effective, significantly reducing mould counts of more than 2 log units at the end of ripening. The application of the adjunct cultures resulted in a delay in mycelial growth of P. chrysogenum and A. flavus inoculated on the cheese surface as well. Finally, we found no significant differences among samples for the sensory parameters evaluated that received similar ratings. Our results indicate that the selected Lactobacillus strains may have a potential effect in controlling mould contamination on cheeses. Further studies are currently being carried out to identify the molecules responsible for the antifungal activity.

Lactobacillus plantarum 5BG Survives During Refrigerated Storage Bio-Preserving Packaged Spanish-Style Table Olives (cv. Bella di Cerignola)

This paper proposes bio-preservation as a tool to assure quality and safety of Spanish-style table olives cv. Bella di Cerignola. Lactobacillus plantarum 5BG was inoculated in ready to sell olives packaged in an industrial plant by using a half-volume brine (4% NaCl; 2% sucrose). The samples were stored at 4°C. The survival of the inoculated strain, the microbiological quality, the sensory scores and the survival of a strain of Listeria monocytogenes inoculated in brines were evaluated. The persistence of the Lb. plantarum bio-preserving culture was confirmed on olives (≥6.5 Log CFU/g) and in brine (≥7 Log CFU/ml). Bio-preserved olives (SET1) showed a better sensory profile than chemically acidified control olives (SET2) and the texture was the real discriminative parameter among samples. Bio-preserved olives recorded better scores during storage because of their ability to retain good hardness, crunchiness, and fibrousness without cracks. The inoculation of Lb. plantarum positively acted on the safety of olives, as the D-value of L. monocytogenes was reduced from 40 (SET2) to 5 days (SET1). In conclusion, Lb. plantarum 5BG and the physico-chemical conditions achieved in the settled procedure are suitable for the industrial packaging of Bella di Cerignola table olives, improving the process by halving brining volumes and avoiding chemical stabilizers, and significantly reducing the salt concentration. The final product is also safely preserved for almost 5 months as suggested by the reduction of the survival rate of L. monocytogenes.

Monitoring Viable Cells of the Biological Control Agent Lactobacillus plantarum PM411 in Aerial Plant Surfaces by Means of a Strain-Specific Viability Quantitative PCR Method

A viability quantitative PCR (v-qPCR) assay was developed for the unambiguous detection and quantification of Lactobacillus plantarum PM411 viable cells in aerial plant surfaces. A 972-bp region of a PM411 predicted prophage with mosaic architecture enabled the identification of a PM411 strain-specific molecular marker. Three primer sets with different amplicon lengths (92, 188, and 317 bp) and one TaqMan probe were designed. All the qPCR assays showed good linearity over a 4-log range and good efficiencies but differed in sensitivity. The nucleic acid-binding dye PEMAX was used to selectively detect and enumerate viable bacteria by v-qPCR. The primer set amplifying a 188-bp DNA fragment was selected as the most suitable for v-qPCR. The performance of the method was assessed on apple blossoms, pear, strawberry, and kiwifruit leaves in potted plants under controlled environmental conditions, as well as pear and apple blossoms under field conditions, by comparing v-qPCR population estimations to those obtained by qPCR and specific plate counting on de Man-Rogosa-Sharpe (MRS)-rifampin. The population estimation did not differ significantly between methods when conditions were conducive to bacterial survival. However, under stressful conditions, differences between methods were observed due to cell death or viable-but-nonculturable state induction. While qPCR overestimated the population level, plate counting underestimated this value in comparison to v-qPCR. PM411 attained stable population levels of viable cells on the flower environment under high relative humidity. However, the unfavorable conditions on the leaf surface and the relatively dryness in the field caused an important decrease in the viable population.

IMPORTANCE The v-qPCR method in combination with plate counting and qPCR is a powerful tool for studies of colonization and survival under field conditions, to improve formulations and delivery strategies of PM411, and to optimize the dose and timing of spray schedules. It is expected that PEMAX v-qPCR could also be developed for monitoring other strains on plant surfaces not only as biological control agents but also beneficial bacteria useful in the sustainable management of crop production.

Characterization and Antibacterial Potential of Lactic Acid Bacterium Pediococcus pentosaceus 4I1 Isolated from Freshwater Fish Zacco koreanus

This study was undertaken to characterize a lactic acid bacterium 4I1, isolated from the freshwater fish, Zacco koreanus. Morphological, biochemical, and molecular characterization of 4I1 revealed it to be Pediococcus pentosaceus 4I1. The cell free supernatant (CFS) of P. pentosaceus 4I1 exhibited significant (p < 0.05) antibacterial effects (inhibition zone diameters: 16.5-20.4 mm) against tested foodborne pathogenic bacteria with MIC and MBC values of 250-500 and 500-1,000 μg/mL, respectively. Further, antibacterial action of CFS of P. pentosaceus 4I1 against two selected bacteria Staphylococcus aureus KCTC-1621 and Escherichia coli O157:H7 was determined in subsequent assays. The CFS of P. pentosaceus 4I1 revealed its antibacterial action against S. aureus KCTC-1621 and E. coli O157:H7 on membrane integrity as confirmed by a reduction in cell viability, increased potassium ion release (900 and 800 mmol/L), reduced absorption at 260-nm (3.99 and 3.77 OD), and increased relative electrical conductivity (9.9 and 9.7%), respectively. Gas chromatography-mass spectrometry (GC-MS) analysis of the CFS of P. pentosaceus 4I1 resulted in the identification of seven major compounds, which included amino acids, fatty acids and organic acids. Scanning electron microscopic-based morphological analysis further confirmed the antibacterial effect of CFS of P. pentosaceus 4I1 against S. aureus KCTC-1621 and E. coli O157:H7. In addition, the CFS of P. Pentosaceus 4I1 displayed potent inhibitory effects on biofilms formation by S. aureus KCTC-1621 and E. coli O157:H7. The study indicates the CFS of P. pentosaceus 4I1 offers an alternative means of controlling foodborne pathogens.

GABA Production in Lactococcus lactis Is Enhanced by Arginine and Co-addition of Malate

Lactococcus lactis NCDO 2118 was previously selected for its ability to decarboxylate glutamate to γ-aminobutyric acid (GABA), an interesting nutritional supplement able to improve mood and relaxation. Amino acid decarboxylation is generally considered as among the biochemical systems allowing lactic acid bacteria to counteracting acidic stress and obtaining metabolic energy. These strategies also include arginine deiminase pathway and malolactic fermentation but little is known about their possible interactions of with GABA production. In the present study, the effects of glutamate, arginine, and malate (i.e., the substrates of these acid-resistance pathways) on L. lactis NCDO 2118 growth and GABA production performances were analyzed. Both malate and arginine supplementation resulted in an efficient reduction of acidity and improvement of bacterial biomass compared to glutamate supplementation. Glutamate decarboxylation was limited to narrow environmental conditions (pH < 5.1) and physiological state (stationary phase). However, some conditions were able to improve GABA production or activate glutamate decarboxylation system even outside of this compass. Arginine clearly stimulated glutamate decarboxylation: the highest GABA production (8.6 mM) was observed in cultures supplemented with both arginine and glutamate. The simultaneous addition of arginine, malate, and glutamate enabled earlier GABA production (i.e., during exponential growth) at relatively high pH (6.5). As far as we know, no previous study has reported GABA production in such conditions. Although further studies are needed to understand the molecular basis of these phenomena, these results represent important keys suitable of application in GABA production processes.

Biocontrol of the Potato Blackleg and Soft Rot Diseases Caused by Dickeya dianthicola

Development of protection tools targeting Dickeya species is an important issue in the potato production. Here, we present the identification and the characterization of novel biocontrol agents. Successive screenings of 10,000 bacterial isolates led us to retain 58 strains that exhibited growth inhibition properties against several Dickeya sp. and/or Pectobacterium sp. pathogens. Most of them belonged to the Pseudomonas and Bacillus genera. In vitro assays revealed a fitness decrease of the tested Dickeya sp. and Pectobacterium sp. pathogens in the presence of the biocontrol agents. In addition, four independent greenhouse assays performed to evaluate the biocontrol bacteria effect on potato plants artificially contaminated with Dickeya dianthicola revealed that a mix of three biocontrol agents, namely, Pseudomonas putida PA14H7 and Pseudomonas fluorescens PA3G8 and PA4C2, repeatedly decreased the severity of blackleg symptoms as well as the transmission of D. dianthicola to the tuber progeny. This work highlights the use of a combination of biocontrol strains as a potential strategy to limit the soft rot and blackleg diseases caused by D. dianthicola on potato plants and tubers.

A natural odor attraction between lactic acid bacteria and the nematode Caenorhabditis elegans

Animal predators can track prey using their keen sense of smell. The bacteriovorous nematode Caenorhabditis elegans employs sensitive olfactory sensory neurons that express vertebrate-like odor receptors to locate bacteria. C. elegans displays odor-related behaviors such as attraction, aversion and adaptation, but the ecological significance of these behaviors is not known. Using a combination of food microbiology and genetics, we elucidate a possible predator-prey relationship between C. elegans and lactic acid bacteria (LAB) in rotting citrus fruit. LAB produces the volatile odor diacetyl as an oxidized by-product of fermentation in the presence of citrate. We show that C. elegans is attracted to LAB when grown on citrate media or Citrus medica L, commonly known as yuzu, a citrus fruit native to East Asia, and this attraction is mediated by the diacetyl odor receptor, ODR-10. We isolated a wild LAB strain and a wild C. elegans-related nematode from rotten yuzu, and demonstrate that the wild nematode was attracted to the diacetyl produced by LAB. These results not only identify an ecological function for a C. elegans olfactory behavior, but contribute to the growing understanding of ecological relationships between the microbial and metazoan worlds.

Phenotypic and genotypic characterization of some lactic Acid bacteria isolated from bee pollen: a preliminary study

In the present work, five hundred and sixty-seven isolates of lactic acid bacteria were recovered from raw bee pollen grains. All isolates were screened for their antagonistic activity against both Gram-positive and Gram-negative pathogenic bacteria. Neutralized supernatants of 54 lactic acid bacteria (LAB) cultures from 216 active isolates inhibited the growth of indicator bacteria. They were phenotypically characterized, based on the fermentation of 39 carbohydrates. Using the simple matching coefficient and unweighted pair group algorithm with arithmetic averages (UPGMA), seven clusters with other two members were defined at the 79% similarity level. The following species were characterized: Lactobacillus plantarum, Lactobacillus fermentum, Lactococcus lactis, Pediococcus acidilactici, Pediococcus pentosaceus, and unidentified lactobacilli. Phenotypic characteristics of major and minor clusters were also identified. Partial sequencing of the 16S rRNA gene of representative isolates from each cluster was performed, and ten strains were assigned to seven species: Lactobacillus plantarum, Lactobacillus fermentum, Lactococcus lactis, Lactobacillus ingluviei, Pediococcus pentosaceus, Lactobacillus acidipiscis and Weissella cibaria. The molecular method used failed to determine the exact taxonomic status of BH0900 and AH3133.

Fungal/mycotic diseases of poultry-diagnosis, treatment and control: a review

Fungal/mycotic diseases cause significant economic losses to the poultry industry either due to their direct infectious nature or due to production of mycotoxins, the secondary fungal metabolites produced in grains or poultry feed. Several fungi have created havoc in the poultry industry and some of them cause direct harm to human health due to their zoonotic implications. They are responsible for high morbidity and mortality, especially in young birds and cause stunted growth and diarrhea; and fatal encephalitis. Mycotic dermatitis is a possible health hazard associated with poultry houses. Mycotoxins are the leading cause of producing immunosuppression in birds, which makes them prone to several bacterial and viral infections leading to huge economic losses to the poultry industry. In comparison to bacterial and viral diseases, advances in diagnosis, treatment, prevention and control of fungal diseases in poultry has not taken much attention. Recently, molecular biological tools have been explored for rapid and accurate diagnosis of important fungal infections. Effective prevention and control measures include: appropriate hygiene, sanitation and disinfection, strict biosecurity programme and regular surveillance/monitoring of fungal infections as well as following judicious use of anti-fungal drugs. Precautionary measures during crop production, harvesting and storing and in feed mixing plants can help to check the fungal infections including health hazards of mycotoxins/mycotoxicosis. The present review describes the fungal pathogens causing diseases in poultry/birds, especially focusing to their diagnosis, prevention and control measures, which would help in formulating appropriate strategies to have a check and control on these unwanted troubles to the poultry producers/farmers.

Diversity and antimicrobial properties of lactic acid bacteria isolated from rhizosphere of olive trees and desert truffles of Tunisia

A total of 119 lactic acid bacteria (LAB) were isolated, by culture-dependant method, from rhizosphere samples of olive trees and desert truffles and evaluated for different biotechnological properties. Using the variability of the intergenic spacer 16S-23S and 16S rRNA gene sequences, the isolates were identified as the genera Lactococcus, Pediococcus, Lactobacillus, Weissella, and Enterococcus. All the strains showed proteolytic activity with variable rates 42% were EPS producers, while only 10% showed the ability to grow in 9% NaCl. In addition, a low rate of antibiotic resistance was detected among rhizospheric enterococci. Furthermore, a strong antibacterial activity against plant and/or pathogenic bacteria of Stenotrophomonas maltophilia, Pantoea agglomerans, Pseudomonas savastanoi, the food-borne Staphylococcus aureus, and Listeria monocytogenes was recorded. Antifungal activity evaluation showed that Botrytis cinerea was the most inhibited fungus followed by Penicillium expansum, Verticillium dahliae, and Aspergillus niger. Most of the active strains belonged to the genera Enterococcus and Weissella. This study led to suggest that environmental-derived LAB strains could be selected for technological application to control pathogenic bacteria and to protect food safety from postharvest deleterious microbiota.

Antimicrobial activity of bacteriocin-producing lactic acid bacteria isolated from cheeses and yogurts

The biopreservation of foods using bacteriocinogenic lactic acid bacteria (LAB) isolated directly from foods is an innovative approach. The objectives of this study were to isolate and identify bacteriocinogenic LAB from various cheeses and yogurts and evaluate their antimicrobial effects on selected spoilage and pathogenic microorganisms in vitro as well as on a food commodity.

LAB were isolated using MRS and M17 media. The agar diffusion bioassay was used to screen for bacteriocin or bacteriocin-like substances (BLS) producing LAB using Lactobacillus sakei and Listeria innocua as indicator organisms. Out of 138 LAB isolates, 28 were found to inhibit these bacteria and were identified as strains of Enterococcus faecium, Streptococcus thermophilus, Lactobacillus casei and Lactobacillus sakei subsp. sakei using 16S rRNA gene sequencing. Eight isolates were tested for antimicrobial activity at 5°C and 20°C against L. innocua, Escherichia coli, Bacillus cereus, Pseudomonas fluorescens, Erwinia carotovora, and Leuconostoc mesenteroides subsp. mesenteroides using the agar diffusion bioassay, and also against Penicillium expansum, Botrytis cinerea and Monilinia frucitcola using the microdilution plate method. The effect of selected LAB strains on L. innocua inoculated onto fresh-cut onions was also investigated.

Twenty percent of our isolates produced BLS inhibiting the growth of L. innocua and/or Lact. sakei. Organic acids and/or H₂O₂ produced by LAB and not the BLS had strong antimicrobial effects on all microorganisms tested with the exception of E. coli. Ent. faecium, Strep. thermophilus and Lact. casei effectively inhibited the growth of natural microflora and L. innocua inoculated onto fresh-cut onions. Bacteriocinogenic LAB present in cheeses and yogurts may have potential to be used as biopreservatives in foods.

Bio-protective potential of lactic acid bacteria isolated from fermented wax gourd

The antifungal activities of 85 lactic acid bacteria strains isolated from fermented wax gourd against the four fungal species, Penicillium oxalicum, Aspergillus flavus, Aspergillus sydowii, and Mucor racemosus, were determined. Inhibitory activity against at least one or more fungal species was observed with 27 Weissella cibaria and 11 Weissella paramesenteroides strains. Among these strains, W. cibaria 861006 and W. paramesenteroides 860509 showed greater inhibitory activities and were therefore selected for further analysis. The results suggested that the antifungal activities were originated from the organic acids produced by W. cibaria 861006 and W. paramesenteroides 860509. The application tests indicated that the growth of P. oxalicum could be effectively inhibited by W. cibaria 861006 for 6 days on grape surfaces. However, W. paramesenteroides 860509 could only remain its inhibition effect for 48 h. The findings obtained in this study suggest the potential use of W. cibaria 861006 as a bio-protective agent against fungi for agricultural purposes or ready-to-eat fresh fruit and vegetable products.

Effect of acid lactic bacteria isolated from faeces of healthy dogs on growth parameters and aflatoxin B1 production by Aspergillus species in vitro

The aim of the present study was to evaluate the inhibitory effect of Enterococcus faecium and Lactococcus lactis subsp. lactis isolated from faeces of healthy dogs on (i) lag phase, (ii) growth rate, and (iii) aflatoxin B1 production by Aspergillus section Flavi on in vitro assays. Thirteen lactic acid bacteria (LAB) isolates were used as antagonist microorganisms. Antagonistic activity was assayed against four potentially aflatoxigenic Aspergillus section Flavi isolates: A. flavus (AF210 and AF281), A. parasiticus (AP245) and A. parasiticus (NRRL 2999). In general, the longest lag phases of Aspergillus isolates were obtained with E. faecium GJ40. Respecting the growth rate, no significant reduction was found in this parameter in the interaction assays with A. flavus and antagonist isolates respecting the control. While in A. parasiticus a significant reduction in growth rate was only observed in the interaction among reference strain and E. faecium MF5 isolate (p < 0.05). In general, AFB1 production was reduced by most of the LAB isolates assayed, except for E. faecium GJ18, GJ20, MF3 and MF4. This study provides the first data about the antiaflatoxigenic activity of autochthonous LAB isolated from dog faeces.

Isolation and characteristics of lactic acid bacteria isolated from ripe mulberries in Taiwan

The objective of this study was to isolate, characterize, and identify lactic acid bacteria (LAB) from ripe mulberries collected in Taiwan. Ripe mulberry samples were collected at five mulberry farms, located in different counties of Taiwan. Eighty-eight acid-producing cultures were isolated from these samples, and isolates were divided into classes first by phenotype, then into groups by restriction fragment length polymorphism (RFLP) analysis and sequencing of 16S ribosomal DNA (rDNA). Phenotypic and biochemical characteristics led to identification of four bacterial groups (A to D). Weissella cibaria was the most abundant type of LAB distributed in four mulberry farms, and Lactobacillus plantarum was the most abundant LAB found in the remaining farm. Ten W. cibaria and one Lactococcus lactis subsp. lactis isolate produced bacteriocins against the indicator strain Lactobacillus sakei JCM 1157^T. These results suggest that various LAB are distributed in ripe mulberries and W. cibaria was the most abundant LAB found in this study.

Inhibition of mycotoxin-producing Aspergillus nomius vsc 23 by lactic acid bacteria and Saccharomyces cerevisiae

The effect of different fermenting microorganisms on growth of a mycotoxin- producing Aspergillus nomius was assayed. Two lactic acid bacteria, Lactobacillus fermentum and Lactobacillus rhamnosus, and Saccharomyces cerevisiae, all of which are widely used in fermentation and preservation of food, were assayed on their fungus inhibitory properties. Assays were carried out by simultaneous inoculation of one of the possible inhibiting microorganisms and the fungus or subsequent inoculation of one of the microorganisms followed by the fungus. All three microorganisms assayed showed growth inhibition of the mycotoxin-producing Aspergillus strain. L. rhamnosus O236, isolated from sheep milk and selected for its technological properties, showed highest fungal inhibition of the microorganisms assayed. The use of antifungal LAB with excellent technological properties rather than chemical preservatives would enable the food industry to produce organic food without addition of chemical substances.