Inhibition of mycotoxin-producing fungi by Bacillus strains isolated from fish intestines

Probiotic-based adsorbent mitigates aflatoxin B1 toxicity in Piaractus mesopotamicus: assessing well-being via changes in tissue architecture and digestive enzyme activity

Aflatoxin is a mycotoxin produced by fungi of the genus Aspergillus that is present in various foods. Probiotics are well-established products in aquaculture, and due to their effective contribution to the intestine, they can be used as an aflatoxin adsorbent. This study evaluated the effects of aflatoxin B1 (AFB1) on enzymatic activity and intestinal function in Piaractus mesopotamicus (pacu) fingerlings fed diets containing a probiotic-based adsorbent (PBA). Seventy-two fish with an average weight of 12 ± 1.30 g were used in the study. The experiment was conducted over 15 days using a completely randomized design with six diet treatments (AFB1 per kg of formulated diet) and two replicates. These treatments were: control without AFB1; 25.0 µg of AFB1; 400.0 µg of AFB1; control diet without AFB1 + PBA; 25.0 µg of AFB1 + PBA; and 400.0 µg of AFB1 + PBA. After the experimental period, the digestive enzymes protease, amylase, and lipase from the stomach, pyloric caeca, and intestine were quantified. The height and width of the intestinal villi, pyloric caeca, and stomach wall were measured. Fish fed the 400.0 µg of AFB1 diet showed reduced feed consumption, even though they ingested higher amounts of AFB1 compared to those fed the other experimental diets. The best zootechnical performance parameters were observed in fish fed the control diet without AFB1 + PBA. Changes (p < 0.05) were observed in the amount of protease in the stomach, pyloric caeca, and intestine; in the amount of amylase in the intestine; and the amount of lipase in the pyloric caeca and intestine. Changes were observed (p < 0.05) in the length of the stomach wall and the anterior and posterior intestines. Changes in the width of the stomach and anterior intestine walls were observed as a result of diet. Our results suggest that the use of probiotics as an aflatoxin adsorbent in pacu diets is beneficial from a physiological perspective and may also enhance growth.

Insights into the antifungal mechanism of Bacillus subtilis cyclic lipopeptide iturin A mediated by potassium ion channel

Fungal infections pose severe and potentially lethal threats to plant, animal, and human health. Ergosterol has served as the primary target for developing antifungal medications. However, many antifungal drugs remain highly toxic to humans due to similarity in cell membrane composition between fungal and animal cells. Iturin A, lipopeptide produced by Bacillus subtilis, efficiently inhibit various fungi, but demonstrated safety in oral administration, indicating the existence of targets different from ergosterol. To pinpoint the exact antifungal target of iturin A, we used homologous recombination to knock out and overexpress erg3, a key gene in ergosterol synthesis. Saccharomyces cerevisiae and Aspergillus carbonarius were transformed using the LiAc/SS-DNNPEG and Agrobacterium-mediated transformation (AMT), respectively. Surprisingly, increasing ergosterol content did not augment antifungal activity. Furthermore, iturin A's antifungal activity against S. cerevisiae was reduced while it pre-incubation with voltage-gated potassium (Kv) channel inhibitor, indicating that Kv activation was responsible for cell death. Iturin A was found to activate the Kv protein, stimulating K+ efflux from cell. In vitro tests confirmed interaction between iturin A and Kv protein. This study highlights Kv as one of the precise targets of iturin A in its antifungal activity, offering a novel target for the development of antifungal medications.

The effects of probiotic-based additives on aflatoxin intoxication in Piaractus mesopotamicus: a study of liver histology and metabolic performance

Mycotoxins, produced by fungi, can contaminate fish food and harm their health. Probiotics enhance immune balance and primarily function in the animal intestine. This study aimed to assess aflatoxin's impact on Piaractus mesopotamicus and explore probiotic-based additive (PBA) benefits in mitigating these effects, focusing on antioxidant activity, biochemical indices, and hepatic histopathology. Two experiments were conducted using P. mesopotamicus fry. The first experimental assay tested various levels of aflatoxin B1 (0.0, 25.0, 50.0, 100.0, 200.0, and 400.0 µg kg-1) over a 10-day period. The second experimental assay examined the efficacy of the probiotic (supplemented at 0.20%) in diets with different levels of aflatoxin B1 (0.0, 25.0, and 400.0 µg kg-1) for 15 days. At the end of each assay, the fish underwent a 24-hour fasting period, and the survival rate was recorded. Six liver specimens from each treatment group were randomly selected for metabolic indicator assays, including superoxide dismutase, catalase, alanine aminotransferase, aspartate aminotransferase, and albumin. Additionally, histopathological analysis was performed on six specimens. The initial study discovered that inclusion rates above 25.0 µg kg-1 resulted in decreased activity of AST (aspartate aminotransferase), ALT (alanine aminotransferase), ALB (albumin), CAT (catalase), and SOD (superoxide dismutase), accompanied by liver histopathological lesions. In the second study, the inclusion of PBA in diets contaminated with AFB1 improved the activity of AST and ALT up to 25.0 µg kg-1 of AFB1, with no histopathological lesions observed. The study demonstrated the hepatoprotective effects of PBA in diets contaminated with AFB1. The enzyme activity and hepatic histopathology were maintained, indicating a reduction in damage caused by high concentrations of AFB1 (400.0 µg kg-1 of AFB1). The adverse effects of AFB1 on biochemical and histopathological parameters were observed from 25.0 µg kg-1 onwards. Notably, PBA supplementation enhanced enzymatic activity at a concentration of 25 µg kg-1 of AFB1 and mitigated the effects at 400.0 µg kg-1 of AFB1. The use of PBAs in pacu diets is highly recommended as they effectively neutralize the toxic effects of AFB1 when added to diets containing 25.0 µg kg-1 AFB1. Dietary inclusion of aflatoxin B1 at a concentration of 25.0 µg kg-1 adversely affects the liver of Piaractus mesopotamicus (Pacu). However, the addition of a probiotic-based additive (PBA) to the diets containing this concentration of aflatoxin neutralized its toxic effects. Therefore, the study recommends the use of PBAs in Pacu diets to mitigate the adverse effects of aflatoxin contamination.

Genomic analysis reveals genes that encode the synthesis of volatile compounds by a Bacillus velezensis-based biofungicide used in the treatment of grapes to control Aspergillus carbonarius

Fungal control strategies based on the use of Bacillus have emerged in agriculture as eco-friendly alternatives to replace/reduce the use of synthetic pesticides. Bacillus sp. P1 was reported as a new promising strain for control of Aspergillus carbonarius, a known producer of ochratoxin A, categorized as possible human carcinogen with high nephrotoxic potential. Grape quality can be influenced by vineyard management practices, including the use of fungal control agents. The aim of this study was to evaluate, for the first time, the quality parameters of Chardonnay grapes exposed to an antifungal Bacillus-based strategy for control of A. carbonarius, supporting findings by genomic investigations. Furthermore, genomic tools were used to confirm that the strain P1 belongs to the non-pathogenic species Bacillus velezensis and also to certify its biosafety. The genome of B. velezensis P1 harbors genes that are putatively involved in the production of volatiles and hydrolytic enzymes, which are responsible for releasing the free form of aroma compounds. In addition to promote biocontrol of phytopathogenic fungi and ochratoxins, the treatment with B. velezensis P1 did not change the texture (hardness and firmness), color and pH of the grapes. Heat map and hierarchical clustering analysis (HCA) of volatiles evaluated by GC/MS revealed that Bacillus-treated grapes showed higher levels of compounds with a pleasant odor descriptions such as 3-hydroxy-2-butanone, 2,3-butanediol, 3-methyl-1-butanol, 3,4-dihydro-β-ionone, β-ionone, dihydroactinidiolide, linalool oxide, and β-terpineol. The results of this study indicate that B. velezensis P1 presents desirable properties to be used as a biocontrol agent.

Genome analysis of Pseudomonas strain 4B with broad antagonistic activity against toxigenic fungi

Pseudomonas sp. 4B isolated from the effluent pond of a bovine abattoir was investigated as antifungal against toxigenic fungi. The complete genome of Pseudomonas 4B was sequenced using the Illumina MiSeq platform. Phylogenetic analysis and genome comparisons indicated that the strain belongs to the Pseudomonas aeruginosa group. In silico investigation revealed gene clusters associated with the biosynthesis of several antifungals, including pyocyanin, rhizomide, thanamycin, and pyochelin. This bacterium was investigated through antifungal assays, showing an inhibitory effect against all toxigenic fungi tested. Bacterial cells reduced the diameter of fungal colonies, colony growth rate, and sporulation of each indicator fungi in 10-day simultaneous growing tests. The co-incubation of bacterial suspension and fungal spores in yeast extract-sucrose broth for 48 h resulted in reduced spore germination. During simultaneous growth, decreased production of aflatoxin B1 and ochratoxin A by Aspergillus flavus and Aspergillus carbonarius, respectively, was observed. Genome analysis and in vitro studies showed the ability of P. aeruginosa 4B to reduce fungal growth parameters and mycotoxin levels, indicating the potential of this bacterium to control toxigenic fungi. The broad antifungal activity of this strain may represent a sustainable alternative for the exploration and subsequent use of its possible metabolites in order to control mycotoxin-producing fungi.

Safety assessment of surfactin-producing Bacillus strains and their lipopeptides extracts in vitro and in vivo

Beneficial Bacillus strains can be administered to livestock as probiotics to improve animal health. Cyclic lipopeptides produced by Bacillus such as surfactins may be responsible for some of the beneficial effects due to their anti-inflammatory and immunomodulatory activity. The aim of the present study was to isolate and evaluate the biocompatibility of native Bacillus spp. strains and their surfactin-like lipopeptides in vitro and in vivo to determine their potential to be used on animals. Biocompatibility of endospore suspensions (10⁸  UFC/mL), and different dilutions (1:10; 1:50; 1:100; 1:500, and 1:1000) of Bacillus lipopeptide extracts containing surfactin was tested on Caco-2 cells by microculture tetrazolium-based colorimetric assay. Genotoxicity was tested on BALB/c mice (n = 6) administered 0.2 mL of endospore suspensions by the bone marrow erythrocyte micronuclei assay. All the isolates tested produced between 26.96 and 239.97 µg mL^{- 1} of surfactin. The lipopeptide extract (LPE) from isolate MFF1.11 demonstrated significant cytotoxicity in vitro. In contrast, LPE from MFF 2.2; MFF 2.7, TL1.11, TL 2.5, and TC12 had no cytotoxic effect (V% > 70%) on Caco-2 cells, not affecting cell viability signifficantly in most treatments. Similarly, none of the endospore suspensions affected cell viability (V% > 80%). Likewise, endospores did not cause genotoxicity on BALB/c mice. This study was elementary as a first step for a new line of research, since it allowed us to choose the safest isolates to keep working on the search of new potentially probiotic strains destined to production animals to improve their performance and health.

Iturin A Strongly Inhibits the Growth and T-2 Toxin Synthesis of Fusarium oxysporum: A Morphological, Cellular, and Transcriptomics Study

Fusarium oxysporum (F. oxysporum) is a common contaminant of dried fish, and the T-2 synthesis by this organism in dried fish products poses a serious public health risk. In this study, we investigated the effects of iturin A, a cyclic lipopeptide produced by Bacillus subtilis, on the growth and synthesis of the T-2 toxin of F. oxysporum, and transcriptomics was conducted. Results showed that the inhibitory effect of iturin A on F. oxysporum was significantly enhanced with an increase in iturin A concentrations. More specifically, compared with the control group, all indexes in the iturin A treatment group with 50 μg/mL were decreased to 24.84 mm, 0.33 × 106 cfu/mL, and 5.86 ng/mL for the colony diameter, number of spores, and concentration of T-2 toxin, respectively. Furthermore, iturin A was proven to destroy the integrity of cell membranes and cause a significant increase in ROS at 25 μg/mL or 50 μg/mL. Transcriptomic analysis revealed that with the treatment of iturin A, the genes of the oxidation-reduction process were up-regulated, while the gene expression of mycelial growth, cell integrity, transmembrane transport, energy metabolism, and others were down-regulated. More importantly, the Tri5 gene cluster was significantly inhibited. This study provided new insights into the mechanism for the inhibitory effect of iturin A on the growth and T-2 toxin synthesis of F. oxysporum and theoretical guidance for the application of iturin A in the preservation of dried aquatic products.

A Bacillus-based biofungicide agent prevents ochratoxins occurrence in grapes and impacts the volatile profile throughout the Chardonnay winemaking stages

Bacillus-based biocontrol agents have emerged as a strategy to eliminate or reduce the use of synthetic fungicides that are detrimental to health and the environment. In vineyards, a special concern arises from the control of Aspergillus carbonarius, a fungus known for its potential to produce ochratoxins. Ochratoxin A (OTA) is the most toxic form among ochratoxins and its maximum limit in wine has been established in Europe and Brazil as 2 μg/kg. Wine quality, especially the volatile profile, may be influenced by the antifungal strategies, since fungicide residues are transferred from grapes to must during winemaking. The objective of this study was to evaluate, for the first time, the impact of a biocontrol strategy containing Bacillus velezensis P1 on the volatile profile and occurrence of ochratoxins when grapes infected with A. carbonarius were used in winemaking. The evaluation of ochratoxins was carried out by liquid chromatography coupled to quadrupole time-of-flight mass spectrometry (LC-QToF-MS), and volatile compounds were analyzed using comprehensive two-dimensional gas chromatography coupled to quadrupole mass spectrometry (GC × GC/qMS). Six ochratoxins were identified in must prepared with Chardonnay grapes inoculated with A. carbonarius (ochratoxin α, ochratoxin β, ochratoxin α methyl-ester, ochratoxin α amide, N-formyl-ochratoxin α amide and OTA). Although winemaking causes a decrease in the levels of all forms of ochratoxins, the co-occurrence of these mycotoxins was verified in wine made with grapes containing A. carbonarius. B. velezensis P1 prevented the occurrence of ochratoxins in must, ensuring the safety of wines. Regarding the volatile profile, a predominant presence of terpenic compounds was verified in samples treated with B. velezensis when compared with those not treated with the biocontrol strategy, whereas the presence of A. carbonarius resulted in a higher concentration of volatile compounds with an odor described as fatty/waxy, possibly compromising wine quality. Therefore, B. velezensis P1 is a new biofungicide possibility to produce ochratoxin-free grapes and high-quality wines.

Reduction of Mycotoxigenic Fungi Growth and Their Mycotoxin Production by Bacillus subtilis QST 713

The use of chemical pesticides to control the occurrence of mycotoxigenic fungi in crops has led to environmental and human health issues, driving the agriculture sector to a more sustainable system. Biocontrol agents such as Bacillus strains and their antimicrobial metabolites have been proposed as alternatives to chemical pesticides. In the present work, a broth obtained from a commercial product containing Bacillus subtilis QST 713 was tested for its ability to inhibit the growth of mycotoxigenic fungi as well as reduce their mycotoxin production. Mass spectrometry analysis of Bacillus subtilis broth allowed to detect the presence of 14 different lipopeptides, belonging to the iturin, fengycin, and surfactin families, already known for their antifungal properties. Bacillus subtilis broth demonstrated to be a useful tool to inhibit the growth of some of the most important mycotoxigenic fungi such as Aspergillus flavus, Fusarium verticillioides, Fusarium graminearum, Aspergillus carbonarius, and Alternaria alternata. In addition, cell-free Bacillus subtilis broth provided the most promising results against the growth of Fusarium graminearum and Alternaria alternata, where the radial growth was reduced up to 86% with respect to the untreated test. With regard to the mycotoxin reduction, raw Bacillus subtilis broth completely inhibited the production of aflatoxin B1, deoxynivalenol, zearalenone, and tenuazonic acid. Cell-free broth provided promising inhibitory properties toward all of the target mycotoxins, even if the results were less promising than the corresponding raw broth. In conclusion, this work showed that a commercial Bacillus subtilis, characterized by the presence of different lipopeptides, was able to reduce the growth of the main mycotoxigenic fungi and inhibit the production of related mycotoxins.

Target Mechanism of Iturinic Lipopeptide on Differential Expression Patterns of Defense-Related Genes against Colletotrichum acutatum in Pepper

Bacillus subtilis KB21 is an isolate with broad spectrum antifungal activity against plant pathogenic fungi. Our aim was to produce and purify antifungal lipopeptides via fermentation using B. subtilis KB21 and verify their antifungal mechanism against pepper anthracnose. When the KB21 strain was cultured in tryptic soy broth medium, the antifungal activity against pepper anthracnose correlated with biosurfactant production. However, there was no antifungal activity when cultured in Luria-Bertani medium. KB21 filtrates showed the highest degree of inhibition of mycelia (91.1%) and spore germination (98.9%) of Colletotrichum acutatum via increases in the biosurfactant levels. Using liquid chromatography-mass spectrometry (LC-MS) and LC-tandem MS (LC-MS/MS) analyses, the component with antifungal activity in the fermentation medium of the KB21 strain was determined to be the cyclic lipopeptide (CLP) antibiotic, iturin A. When the iturin fractions were applied to pepper fruits inoculated with conidia of C. acutatum, the lesion diameter and hyphal growth on the fruit were significantly suppressed. In addition, iturin CLP elevated the gene expression of PAL, LOX, and GLU in the treatments both with and without following fungal pathogens. Overall, the results of this study show that iturin CLPs from B. subtilis KB21 may be potential biological control agents for plant fungal diseases.

Antifungal Peptides and Proteins to Control Toxigenic Fungi and Mycotoxin Biosynthesis

The global challenge to prevent fungal spoilage and mycotoxin contamination on food and feed requires the development of new antifungal strategies. Antimicrobial peptides and proteins (AMPs) with antifungal activity are gaining much interest as natural antifungal compounds due to their properties such as structure diversity and function, antifungal spectrum, mechanism of action, high stability and the availability of biotechnological production methods. Given their multistep mode of action, the development of fungal resistance to AMPs is presumed to be slow or delayed compared to conventional fungicides. Interestingly, AMPs also accomplish important biological functions other than antifungal activity, including anti-mycotoxin biosynthesis activity, which opens novel aspects for their future use in agriculture and food industry to fight mycotoxin contamination. AMPs can reach intracellular targets and exert their activity by mechanisms other than membrane permeabilization. The mechanisms through which AMPs affect mycotoxin production are varied and complex, ranging from oxidative stress to specific inhibition of enzymatic components of mycotoxin biosynthetic pathways. This review presents natural and synthetic antifungal AMPs from different origins which are effective against mycotoxin-producing fungi, and aims at summarizing current knowledge concerning their additional effects on mycotoxin biosynthesis. Antifungal AMPs properties and mechanisms of action are also discussed.

Aspergillus carbonarius-derived ochratoxins are inhibited by Amazonian Bacillus spp. used as a biocontrol agent in grapes

Bacillus spp. have been used as a biocontrol strategy to eliminate/reduce toxic fungicides in viticulture. Furthermore, the presence of fungi that are resistant to commonly used products is frequent, highlighting the need for new biocontrol strains. Aspergillus carbonarius can produce ochratoxins, including ochratoxin A (OTA), which has a regulatory maximum allowable limit for grape products. The purpose of this study was to assess the ability of four Amazonian strains of Bacillus (P1, P7, P11, and P45) to biocontrol A. carbonarius and various forms of ochratoxins in grapes. Berries treated with strain P1 presented no fungal colonies (100% reduction), while P7, P11 and P45 strains caused a reduction of 95, 95 and 61% on fungal counts, respectively. Six forms of ochratoxin were found in the grapes inoculated with A. carbonarius, including ochratoxin α, ochratoxin β, ochratoxin α methyl-ester, ochratoxin α amide, N-formyl-ochratoxin α amide, and OTA. Four of these ochratoxin forms (ochratoxin β, ochratoxin α methyl-ester, ochratoxin α amide, N-formyl-ochratoxin α amide) are reported for the first time in grapes. These ochratoxins were identified using liquid chromatography coupled to quadrupole time-of-flight mass spectrometry (LC-QToF-MS). All Bacillus strains inhibited the synthesis of OTA, which is the most toxic form of ochratoxin. No ochratoxin form was found when P1 and P7 were used. Although some forms of ochratoxin were detected in grapes treated with Bacillus spp. P11 and P45, the levels decreased by 97%. To our knowledge, this is the first report on the inhibition of Aspergillus carbonarius-derived ochratoxin by Bacillus species. P1 strain, identified as Bacillus velezensis, was found to be the most promising for completely inhibiting fungal growth and production of all ochratoxins.

Method for high-throughput antifungal activity screening of bacterial strain libraries

Our laboratory developed a high-throughput screen for antifungal phenotypes in which bacterial libraries in 96-well format are transferred to agar pour plates inoculated with spores of the target fungus. This method is an improvement over bacterial/fungal coculture plate methods that measure antifungal activity as inhibition of radial fungal growth.

Potential of Bacillus velezensis as a probiotic in animal feed: a review

Bacillus velezensis is a plant growth-promoting bacterium that can also inhibit plant pathogens. However, based on its properties, it is emerging as a probiotic in animal feed. This review focuses on the potential characteristics of B. velezensis for use as a probiotic in the animal feed industry. The review was conducted by collecting recently published articles from peer-reviewed journals. Google Scholar and PubMed were used as search engines to access published literature. Based on the information obtained, the data were divided into three groups to discuss the (i) probiotic characteristics of B. velezensis, (ii) probiotic potential for fish, and (iii) the future potential of this species to be developed as a probiotic for the animal feed industry. Different strains of B. velezensis isolated from different sources were found to have the ability to produce antimicrobial compounds and have a beneficial effect on the gut microbiota, with the potential to be a candidate probiotic in the animal feed industry. This review provides valuable information about the characteristics of B. velezensis, which can provide researchers with a better understanding of the use of this species in the animal feed industry.

Rhamnolipids inhibit aflatoxins production in Aspergillus flavus by causing structural damages in the fungal hyphae and down-regulating the expression of their biosynthetic genes

Aflatoxins are hepatotoxic and carcinogenic fungal secondary metabolites that usually contaminate crops and represent a serious health hazard for humans and animals worldwide. In this work, the effect of rhamnolipids (RLs) produced by Pseudomonas aeruginosa #112 on the growth and aflatoxins production by Aspergillus flavus MUM 17.14 was studied in vitro. At concentrations between 45 and 1500 mg/L, RLs reduced the mycelial growth of A. flavus by 23-40% and the production of aflatoxins by 93.9-99.5%. Purified mono-RLs and di-RLs exhibited a similar inhibitory activity on fungal growth. However, the RL mixture had a stronger inhibitory effect on aflatoxins production at concentrations up to 190 mg/L, probably due to a synergistic effect resulting from the combination of both congeners. Using transmission electron microscopy, it was demonstrated that RLs damaged the cell wall and the cytoplasmic membrane of the fungus, leading to the loss of intracellular content. This disruptive phenomenon explains the growth inhibition observed. Furthermore, RLs down-regulated the expression of genes aflC, aflE, aflP and aflQ involved in the aflatoxins biosynthetic pathway (6.4, 44.3, 38.1 and 2.0-fold, respectively), which is in agreement with the almost complete inhibition of aflatoxins production. Overall, the results herein gathered demonstrate for the first time that RLs could be used against aflatoxigenic fungi to attenuate the production of aflatoxins, and unraveled some of their mechanisms of action.

Antifungal potential against Sclerotinia sclerotiorum (Lib.) de Bary and plant growth promoting abilities of Bacillus isolates from canola (Brassica napus L.) roots

Endophytic bacteria show important abilities in promoting plant growth and suppressing phytopathogens, being largely explored in agriculture as biofertilizers or biocontrol agents. Bacteria from canola roots were isolated and screened for different plant growth promotion (PGP) traits and biocontrol of Sclerotinia sclerotiorum. Thirty isolates belonging to Bacillus, Paenibacillus, Lysinibacillus, and Microbacterium genera were obtained. Several isolates produced auxin, siderophores, hydrolytic enzymes, fixed nitrogen and solubilized phosphate. Five isolates presented antifungal activity against S. sclerotiorum by the dual culture assay and four of them also inhibited fungal growth by volatile organic compounds production. All antagonistic isolates belonged to the Bacillus genus, and had their genomes sequenced for the search of biosynthetic gene clusters (BGC) related to antimicrobial metabolites. These isolates were identified as Bacillus safensis (3), Bacillus pumilus (1), and Bacillus megaterium (1), using the genomic metrics ANI and dDDH. Most strains showed several common BGCs, including bacteriocin, polyketide synthase (PKS), and non-ribosomal peptide synthetase (NRPS), related to pumilacidin, bacillibactin, bacilysin, and other antimicrobial compounds. Pumilacidin-related mass peaks were detected in acid precipitation extracts through MALDI-TOF analysis. The genomic features demonstrated the potential of these isolates in the suppression of plant pathogens; however, some aspects of plant-bacterial interactions remain to be elucidated.

Characterization and inhibition of four fungi producing citrinin in various culture media

PURPOSE

This study aimed to investigate the effects of different fermentation conditions (culture medium, temperature, incubation time, pH value and additive) on citrinin production by four fungi.

RESULTS

Among the culture media, potato dextrose medium had lowest citrinin production, followed by yeast sucrose medium and monosodium glutamate medium. The lowest citrinin contents were produced by Monascus anka (M. anka) in potato dextrose medium and yeast sucrose medium, Aspergillus oryzae AS3.042 (A. oryzae) produced the lowest citrinin production in monosodium glutamate medium. The optimum fermentation temperatures for citrinin production by Aspergillus niger (A. niger) and Penicillium citrinum (P. citrinum) were at 30 °C, whereas those by M. anka and A. oryzae were at 35 °C. Citrinin synthesis by four fungi were completely inhibited with a pH value of less than 5.4. By adding ethylene diamine tetraacetic acid (EDTA) or triammonium citrate into monosodium glutamate medium, citrinin production by A. oryzae and A. niger were totally inhibited. Ammonium sulfate completely inhibited citrinin production by A. oryzae, M. anka and P. citrinum, and ammonium nitrate completely inhibited citrinin production by A. oryzae.

CONCLUSIONS

These results indicated that the suitable fermentation conditions could make considerable contributions to the reduction of citrinin production. This study provided an effective way for decreasing the citrinin production.

Diversity of cyclic antimicrobial lipopeptides from Bacillus P34 revealed by functional annotation and comparative genome analysis

Cyclic lipopeptides (CLPs) from Bacillus strains have demonstrated a wide range of bioactivities making them interesting candidates for different applications in the pharmaceutical, food and biotechnological industries. Genome sequencing, together with phylogenetic analysis of the Bacillus sp. P34, isolated from a freshwater fish gut, showed that the bacterial strain belongs to the Bacillus velezensis group. In silico investigation of metabolic gene clusters of nonribosomal peptide synthetases (NRPS) revealed the genetic elements associated with the synthesis of surfactin, fengycin and iturin family component bacillomycin. Further, an assay was conducted to investigate the production of CLPs in the presence of heat inactivated bacterial cultures or fungal spores. Maximum fengycin concentration was observed at 24 h (2300-2700 mg/mL), while maximum iturin amounts were detected at 48 h (250 mg/mL) in the presence of heat-inactivated spores of Aspergillus niger. Heat-inactivated cells of Listeria monocytogenes caused a reduction of both fengycin and iturin amounts. The production of fengycins A and B and the iturin family component bacillomycin L was confirmed by mass spectrometry analyses. This study reinforces the potential of B. velezensis P34 as a valuable strain for biotechnological production of CLPs recognized as important antimicrobial substances.

The Aspergilli and Their Mycotoxins: Metabolic Interactions With Plants and the Soil Biota

Species of the highly diverse fungal genus Aspergillus are well-known agricultural pests, and, most importantly, producers of various mycotoxins threatening food safety worldwide. Mycotoxins are studied predominantly from the perspectives of human and livestock health. Meanwhile, their roles are far less known in nature. However, to understand the factors behind mycotoxin production, the roles of the toxins of Aspergilli must be understood from a complex ecological perspective, taking mold-plant, mold-microbe, and mold-animal interactions into account. The Aspergilli may switch between saprophytic and pathogenic lifestyles, and the production of secondary metabolites, such as mycotoxins, may vary according to these fungal ways of life. Recent studies highlighted the complex ecological network of soil microbiotas determining the niches that Aspergilli can fill in. Interactions with the soil microbiota and soil macro-organisms determine the role of secondary metabolite production to a great extent. While, upon infection of plants, metabolic communication including fungal secondary metabolites like aflatoxins, gliotoxin, patulin, cyclopiazonic acid, and ochratoxin, influences the fate of both the invader and the host. In this review, the role of mycotoxin producing Aspergillus species and their interactions in the ecosystem are discussed. We intend to highlight the complexity of the roles of the main toxic secondary metabolites as well as their fate in natural environments and agriculture, a field that still has important knowledge gaps.

Control of Aflatoxigenic Molds by Antagonistic Microorganisms: Inhibitory Behaviors, Bioactive Compounds, Related Mechanisms, and Influencing Factors

Aflatoxin contamination has been causing great concern worldwide due to the major economic impact on crop production and their toxicological effects to human and animals. Contamination can occur in the field, during transportation, and also in storage. Post-harvest contamination usually derives from the pre-harvest infection of aflatoxigenic molds, especially aflatoxin-producing Aspergilli such as Aspergillusflavus and A. parasiticus. Many strategies preventing aflatoxigenic molds from entering food and feed chains have been reported, among which biological control is becoming one of the most praised strategies. The objective of this article is to review the biocontrol strategy for inhibiting the growth of and aflatoxin production by aflatoxigenic fungi. This review focuses on comparing inhibitory behaviors of different antagonistic microorganisms including various bacteria, fungi and yeasts. We also reviewed the bioactive compounds produced by microorganisms and the mechanisms leading to inhibition. The key factors influencing antifungal activities of antagonists are also discussed in this review.

Potential of Pantoea dispersa as an effective biocontrol agent for black rot in sweet potato

Biocontrol offers a promising alternative to synthetic fungicides for the control of a variety of pre- and post-harvest diseases of crops. Black rot, which is caused by the pathogenic fungus Ceratocytis fimbriata, is the most destructive post-harvest disease of sweet potato, but little is currently known about potential biocontrol agents for this fungus. Here, we isolated several microorganisms from the tuberous roots and shoots of field-grown sweet potato plants, and analyzed their ribosomal RNA gene sequences. The microorganisms belonging to the genus Pantoea made up a major portion of the microbes residing within the sweet potato plants, and fluorescence microscopy showed these microbes colonized the intercellular spaces of the vascular tissue in the sweet potato stems. Four P. dispersa strains strongly inhibited C. fimbriata mycelium growth and spore germination, and altered the morphology of the fungal hyphae. The detection of dead C. fimbriata cells using Evans blue staining suggested that these P. dispersa strains have fungicidal rather than fungistatic activity. Furthermore, P. dispersa strains significantly inhibited C. fimbriata growth on the leaves and tuberous roots of a susceptible sweet potato cultivar (“Yulmi”). These findings suggest that P. dispersa strains could inhibit black rot in sweet potato plants, highlighting their potential as biocontrol agents.

Effect on Serum Parameters and Immune Responses of Carassius auratus gibelio Exposed to Dietary Lead and Bacillus subtilis

Lead (Pb), a heavy metal and an environmental stressor, may affect many physiological processes, including the serum index and the immune response. The aim of this study was to explore the toxic effects of Pb on the serum index and the immune response of Carassius auratus gibelio (C. gibelio) fed 0, 120, or 240 mg/kg Pb, and 10⁹ cfu/g Bacillus subtilis (B. subtilis). After 15 and 30 days of dietary exposure, the serum indices and the immune responses of the fish were assessed. Dietary Pb exposure significantly affected various components of the serum index, including calcium, magnesium, glucose, cholesterol, total protein, glutamic-pyruvic transaminase (ALT), aspartate transaminase (AST), alkaline phosphatase (ALP), and lactate dehydrogenase (LDH). However, sIgA activity in the gut increased significantly following B. subtilis supplementation. Notable changes were also observed in the expression levels of immune-related genes, including HSP70, IgM, HSP90, IL-1β, IL-6, and TNF-α. B. subtilis supplementation effectively attenuated the effects of dietary Pb exposure.

Repressed Beauveria bassiana infections in Delia antiqua due to associated microbiota

BACKGROUND

Insects form both mutualistic and antagonistic relationships with microbes, and some antagonistic microbes have been used as biocontrol agents (BCAs) in pest management. Contextually, BCAs may be inhibited by beneficial insect symbionts, which can become potential barriers to entomopathogen-dependent pest biocontrol. Using the symbioses formed by one devastating dipteran pest, Delia antiqua, and its associated microbes as a model system, we sought to determine whether the antagonistic interaction between BCAs and microbial symbionts could affect the outcome of entomopathogen-dependent pest biocontrol.

RESULTS

The result showed that in contrast to non-axenic D. antiqua larvae, i.e., onion maggots, axenic larvae lost resistance to the entomopathogenic Beauveria bassiana, and the re-inoculation of microbiota increased the resistance of axenic larvae to B. bassiana. Furthermore, bacteria frequently isolated from larvae, including Citrobacter freundii, Enterobacter ludwigii, Pseudomonas protegens, Serratia plymuthica, Sphingobacterium faecium and Stenotrophomonas maltophilia, suppressed B. bassiana conidia germination and hyphal growth, and the re-inoculation of specific individual bacteria enhanced the resistance of axenic larvae to B. bassiana.

CONCLUSION

Bacteria associated with larvae, including C. freundii, E. ludwigii, P. protegens, S. plymuthica, S. faecium and S. maltophilia, can inhibit B. bassiana infection. Removing the microbiota can suppress larval resistance to fungal infection. © 2018 Society of Chemical Industry.