Biocontrol of Aspergillus flavus in Ensiled Sorghum by Water Kefir Microorganisms

The bacterial and yeast microbiota in livestock forages in Hungary

BACKGROUND

Along bacteria, yeasts are common in forages and forage fermentations as spoilage microbes or as additives, yet few studies exist with species-level data on these fungi's occurrence in feedstuff. Active dry yeast and other yeast-based products are also common feed additives in animal husbandry. Here, we aimed to characterize both fermented and non-fermented milking cow feedstuff samples from Hungary to assess their microbial diversity in the first such study from Central Europe.

RESULTS

We applied long-read bacterial metabarcoding to 10 fermented and 25 non-fermented types of samples to assess bacterial communities and their characteristics, surveyed culturable mold and yeast abundance, and identified culturable yeast species. Fermented forages showed the abundance of Aerococcaceae, Bacillaceae, Brucellaceae, Lactobacillaceae, Staphylococcaceae, and Thermoactinomycetaceae, non-fermented ones had Cyanothecaceae, Enterobacteriaceae, Erwiniaceae, Gomontiellaceae, Oxalobacteraceae, Rhodobiaceae, Rickettsiaceae, and Staphylococcaceae. Abundances of bacterial families showed mostly weak correlation with yeast CFU numbers, only Microcoleaceae (positive) and Enterococcaceae and Alcaligenaceae (negative correlation) showed moderate correlation. We identified 14 yeast species, most commonly Diutina rugosa, Pichia fermentans, P. kudriavzevii, and Wickerhahomyces anomalus. We recorded S. cerevisiae isolates only from animal feed mixes with added active dry yeast, while the species was completely absent from fermented forages. The S. cerevisiae isolates showed high genetic uniformity.

CONCLUSION

Our results show that both fermented and non-fermented forages harbor diverse bacterial microbiota, with higher alpha diversity in the latter. The bacterial microbiome had an overall weak correlation with yeast abundance, but yeasts were present in the majority of the samples, including four new records for forages as a habitat for yeasts. Yeasts in forages mostly represented common species including opportunistic pathogens, along with a single strain of Saccharomyces used as a feed mix additive.

Microbial viability and nutritional content of water kefir grains under different storage conditions

Water kefir grains are an important source of probiotics, mainly containing lactic acid bacteria and yeasts. The aim of this study is to investigate the changes in microbial and chemical properties of water kefir grains during 1-month storage at +4°C and -18°C. The initial content of lactobacilli, lactococci, and yeast in water kefir grains was 6.06, 6.33, and 5.93 log CFU/g, respectively. The number of lactobacilli, Lactobacillus acidophilus, and Bifidobacterium spp. in the water kefir grains were comparable, with slight changes at the end of refrigerated storage (p > .05). Lactococci and yeasts decreased significantly after both storage conditions compared to the initial content (p < .05). The dry matter and ash contents remained unchanged during storage (p > .05). Water kefir grains contained significant amounts of calcium, vitamin B2, vitamin B6, vitamin B7, and vitamin B12. Storage at both +4°C and -18°C did not affect the mineral and vitamin contents, except for Cu and Vitamin B2. The results indicate that the water kefir grains remained viable after storage at both temperatures. If water kefir grains need to be stored, it is recommended to store them at +4°C in sugared water as it ensures better survivability of the microbiota of the grains.

Mitigating aflatoxin B1 in high-moisture sorghum silage: Aspergillus flavus growth and aflatoxin B1 prediction

Aspergillus flavus (A. flavus), a frequent contaminant in silage, is a significant producer of aflatoxins, notably the potent carcinogen aflatoxin B1. This contaminant poses a potential risk during the initial aerobic phase of ensiling. The present work studied the impact of temperature on A. flavus growth and aflatoxin B1 production in laboratory-scale sorghum silos during the initial aerobic phase. Growth curves of A. flavus were generated at various temperatures and modeled with the Gompertz model. Results indicated that the optimal temperature range for the maximum growth rate in sorghum mini-silos is between 25 and 30°C. Mold biomass and aflatoxin B1 levels were quantified using qPCR and HPLC, respectively. A predictive model for aflatoxin B1 synthesis in the initial ensiling phase was established, in function of grain moisture, external temperature, and time. Within the studied range, A. flavus's initial concentration did not significantly influence aflatoxin B1 production. According to the model maximum aflatoxin production is expected at 30% moisture and 25°C temperature, after 6 days in the aerobic phase. Aflatoxin B1 production in such conditions was corroborated experimentally. Growth curves and aflatoxin B1 production highlighted that at 48 h of incubation under optimal conditions, aflatoxin B1 concentrations in mini-silos exceeded national legislation limits, reaching values close to 100 ppb. These results underscore the risk associated with A. flavus presence in ensiling material, emphasizing the importance of controlling its development in sorghum silos.

Vibrio gazogenes-dependent disruption of aflatoxin biosynthesis in Aspergillus flavus: the connection with endosomal uptake and hyphal morphogenesis

Aflatoxins, a family of fungal secondary metabolites, are toxic and carcinogenic compounds that pose an enormous threat to global food safety and agricultural sustainability. Specifically agricultural products in African, Southeast Asian and hot and humid regions of American countries suffer most damage from aflatoxin producing molds due to the ideal climate conditions promoting their growth. Our recent studies suggest that Vibrio gazogenes (Vg), an estuarine bacterium non-pathogenic to plants and humans, can significantly inhibit aflatoxin biosynthesis in the producers. In this study, we investigated the mechanism underlying Vg-dependent aflatoxin inhibition using the prominent aflatoxin producer, Aspergillus flavus. We show that aflatoxin inhibition upon Vg treatment was associated with fungal uptake of Vg-prodigiosin, a red pigment, which was consistently visible inside fungal hyphae during treatment. The association of prodigiosin with aflatoxin inhibition was further evident as Serratia marcescens, another prodigiosin producer, significantly inhibited aflatoxin, while non-producers like Escherichia coli, Staphylococcus aureus, Vibrio harveyi, and Vibrio fischeri did not. Also, pure prodigiosin significantly inhibited aflatoxin biosynthesis. Endocytosis inhibitors, filipin and natamycin, reduced the Vg-prodigiosin uptake by the fungus leading to a significant increase in aflatoxin production, suggesting that uptake is endocytosis-dependent. The Vg treatment also reduced hyphal fusion (>98% inhibition) and branching, which are both endosome-dependent processes. Our results, therefore, collectively support our theory that Vg-associated aflatoxin inhibition is mediated by an endocytosis-dependent uptake of Vg-prodigiosin, which possibly leads to a disruption of normal endosomal functions.

Prevention of DSS-induced colitis in mice with water kefir microbiota via anti-inflammatory and microbiota-balancing activity

Water kefir, a natural and stable functional microbiota system consisting of a symbiotic mixture of probiotics, shows multiple bioactivities but little is known about the effect of water kefir microbiota on the prevention of inflammatory bowel disease (IBD), which is one of the most common intestinal problems and has become a worldwide public health concern. Here, the main objectives of the present study were to investigate the preventative effects of water kefir microbiota, a probiotic consortium mainly consisting of bacteria belonging to Acetobacter, Lactobacillus, and Komagataeibacter and fungi belonging to Saccharomyces and Talaromyces, in a dextran sodium sulfate (DSS)-induced colitis mouse model and unveil the underlying mechanism of the action. Water kefir microbiota effectively improved the disease severity of DSS-induced colitis, including decreased body weight and colon length, increased spleen index and DAI score, and colonic tissue damage. Moreover, water kefir microbiota restored the abnormal expression of tight junction proteins (such as occludin, ZO-1, and claudin-1) and pro-inflammatory and anti-inflammatory cytokines (such as IL-1β, IL-6, TNF-α, COX-2, iNOS, and IL-10) and inactivated TLR4-MyD88-NF-κB pathway induced by DSS. Water kefir microbiota also improved the composition and metabolism of intestinal microbiota. These findings demonstrated that water kefir microbiota could exert protective roles in the DSS-induced colitis mouse model by reducing inflammation and regulating microbial dysbiosis, which will be helpful for the development of water kefir microbiota-based microbial products as an alternative preventative strategy for IBD.

Detoxifying mycotoxins and antifungal properties of two rumen-derived Enterococcus species in artificially contaminated corn silages

BACKGROUND

Mycotoxins contamination in food and feed has emerged as an issue of serious concern because they pose serious health risks to both humans and livestock. The study aimed to evaluate the effects of two rumen-derived Enterococcus spp. on fermentation and hygienic quality of artificially contaminated corn silages. The toxigenic fungal-infested (FI) and non-fungal infested (NFI) corn was harvested at 1/2 milk line stage and ensiled without additives (CON) or with Enterococcus faecalis (E) or Enterococcus faecium (M).

RESULTS

The pH of FI silages was higher than that of NFI silages, the pH in NFI-M was lower than in NFI-CON. Inoculating E. faecium markedly increased lactic acid concentration compared to CON and E silages. Both E. faecium and E. faecalis decreased the deoxynivalenol (DON) and zearalenone (ZEN) concentrations compared with the CON for FI silages, while E. faecium was more effective in eliminating aflatoxin B₁ (AFB₁ ). The FI silage had higher bacterial and fungal Shannon indexes than NFI silages. The relative abundance (RA) of Aspergillus and Fusarium marked a decline from day 5 to day 90. Inoculating E. faecium and E. faecalis reduced the RA of Penicillium compared to CON. In vitro mycotoxins removal assay indicated that E. faecium was more effective in AFB₁ detoxification while having lower detoxifying ZEN capacity than E. faecalis.

CONCLUSION

Inoculating rumen-derived Enterococcus spp. isolates alleviated the negative effects of fungal infestation on the fermentation and hygienic quality of corn silages by changing the microbial communities and detoxifying mycotoxins. © 2023 Society of Chemical Industry.

Characterization of kefir yeasts with antifungal capacity against Aspergillus species

Kefir is a fermented probiotic drink obtained by placing kefir granules in a suitable substrate. The kefir granules are a consortium of bacteria and yeasts embedded in a exopolysaccharide matrix. The aim of this research was the isolation and identification of yeasts from kefir of different origin, the evaluation of their antifungal capacity against Aspergillus spp., and the characterization of virulence related traits. Using RFLP of ITS1/ITS4 region, D1/D2 region sequencing, and RAPD techniques, 20 kefir isolates were identified as Geotrichum candidum, Pichia kudriavzevii, Pichia membranifaciens, Saccharomyces cerevisiae, and Candida ethanolica. Their antifungal capacity was evaluated by their conidia germination reduction, which allowed the selection of eight isolates with high to moderate conidia germination reduction against Aspergillus flavus and Aspergillus parasiticus. Furthermore, these selected isolates showed growth inhibition on contact in the dual culture assay for both Aspergillus species and 3 of them-belonging to S. cerevisiae and P. kudriavzevii species-generated volatile organic compounds which significantly affected the growth of both fungi. For the evaluation of virulence-related traits, growth at high temperatures, enzymatic activities, and the adhesion to Caco-2 cells were analyzed. The isolates did not present more than one positive virulence-related trait simultaneously. In particular, it is important to highlight that the adhesion capacity to the model of intestinal barrier was extremely low for all of them. According to the results obtained, further studies would be of interest for the possible use of these promising yeasts as biocontrol agents against fungi in food.

Water kefir: Factors affecting grain growth and health-promoting properties of the fermented beverage

Nowadays, the interest in the consumption of healthy foods has increased as well as the homemade preparation of artisanal fermented product. Water kefir is an ancient drink of uncertain origin, which has been passed down from generation to generation and is currently consumed practically all over the world. Considering the recent and extensive updates published on sugary kefir, this work aims to shed light on the scientific works that have been published so far in relation to this complex ecosystem. We focused our review evaluating the factors that affect the beverage microbial and chemical composition that are responsible for the health attribute of water kefir as well as the grain growth. The microbial ecosystem that constitutes the grains and the fermented consumed beverage can vary according to the fermentation conditions (time and temperature) and especially with the use of different substrates (source of sugars, additives as fruits and molasses). In this sense, the populations of microorganisms in the beverage as well as the metabolites that they produce varies and in consequence their health properties. Otherwise, the knowledge of the variables affecting grain growth are also discussed for its relevance in maintenance of the starter biomass as well as the use of dextran for technological application.

Effect of Different Kefir Source on Fermentation, Aerobic Stability, and Microbial Community of Alfalfa Silage

Simple Summary

Minimizing silage additives cost while increasing silage quality is important for a sustainable livestock enterprise, especially in undeveloped and developing countries. In this study, therefore, commercially available kefir yeast (CK) and homemade kefir culture (HK), as a low-cost additive, was applied at untreated a common control (CON) and three different application doses (5.0, 5.7, and 6.0 log cfu g⁻¹) on wilted alfalfa and evaluated with the fermentation characteristics and aerobic stability. The addition of HK with an application dose greater than 5.0 log cfu g⁻¹ prevents mold formation and inhibits yeast counts in silages. Indeed, both CK and HK improve the silage quality and aerobic stability of alfalfa even with low water-soluble carbohydrate content.

Abstract

The present study has been one of the first attempts to thoroughly examine the effects of different kefir sources on fermentation characteristics, aerobic stability, and microbial communities of alfalfa silages. The effects of commercial kefir (CK) and homemade kefir culture (HK) applied with untreated a common control (CON) and three different application doses (5.0, 5.7, and 6.0 log cfu g⁻¹) on wilted alfalfa and stored at an ambient temperature of 25–30 °C are studied. After 45 days of ensiling, fermentation characteristics and aerobic stability of silages were measured, and bacterial diversity was investigated by 16S ribosomal RNA gene sequencing using the GenomeLab™ GeXP platform. Both CK and HK accelerate more lactic acid production and reduced ammonia nitrogen concentration. Factor analysis of kefir sources suggests that the addition of kefir improves the aerobic stability of silages, even the initial water-soluble carbohydrate (WSC) content is inadequate via its antimicrobial effect on yeast and mold formation. Enterococcus faecium, Pediococcus pentosaceous and Lactobacillus brevis were dominant bacterial species among the treated groups at silo opening, while Lactobacillus plantarum and Lactobacillus brevis became dominant bacterial species after 7 days of aerobic exposure. In conclusion, the application of kefir on alfalfa silages improves fermentation quality and aerobic stability even with low WSC content.

An update on water kefir: Microbiology, composition and production

Water kefir is a sparkling, slightly acidic fermented beverage produced by fermenting a solution of sucrose, to which dried fruits have been added, with water kefir grains. These gelatinous grains are a symbiotic culture of bacteria and yeast embedded in a polysaccharide matrix. Lactic acid bacteria, yeast and acetic acid bacteria are the primary microbial members of the sugary kefir grain. Amongst other contributions, species of lactic acid bacteria produce the exopolysaccharide matrix from which the kefir grain is formed, while yeast assists the bacteria by a nitrogen source that can be assimilated. Exactly which species predominate within the grain microbiota, however, appears to be dependent on the geographical origin of the grains and the fermentation substrate and conditions. These factors ultimately affect the characteristics of the beverage produced in terms of aroma, flavour, and acidity, for example, but can also be controlled and exploited in the production of a beverage of desired characteristics. The production of water kefir has traditionally occurred on a small scale and the use of defined starter cultures is not commonly practiced. However, as water kefir increases in popularity as a beverage - in part because of consumer lifestyle trends and in part due to water kefir being viewed as a health drink with its purported health benefits - the need for a thorough understanding of the biology and dynamics of water kefir, and for defined and controlled production processes, will ultimately increase. The aim of this review is to provide an update into the current knowledge of water kefir.

Microbiota succession during aerobic stability of maize silage inoculated with Lentilactobacillus buchneri NCIMB 40788 and Lentilactobacillus hilgardii CNCM-I-4785

Aerobic deterioration of silage following feeding out is responsible for the deterioration of its quality. Inoculation of silage with lactic acid bacteria is one strategy to limit these effects. A trial was performed using whole‐plant corn ensiled in bag silo, and forage was inoculated with Lentilactobacillus buchneri NCIMB 40788 (Lactobacillus buchneri) and Lentilactobacillus hilgardii CNCM‐I‐4785 (Lactobacillus hilgardii) or not (Control silage). After 159 days of fermentation, the silos were opened and the silage was sampled at 24‐h intervals during a 10‐day aerobic stability assay to measure pH, the fermentation profile, mycotoxins, and microbial and fungal populations. In inoculated silage, lactic acid concentrations and pH remained stable during the aerobic phase and higher microorganism alpha‐diversity was observed. Treated silage was characterized by a high abundance of Saccharomycetes and maintenance of Lactobacillus throughout the aerobic stability assay. The high aerobic stability of the inoculated silage contrasted with the decrease in lactic acid contents and the increase in pH observed in the Control silage, concomitantly with an increase in lactate‐assimilating yeast (Pichia and Issatchenkia), and in Acetobacter and Paenibacillus OTUs. Remarkably, Penicillium and roquefortine C were detected in this silage by day 8 following exposure to air. Our study highlighted the fact that the use of L. buchneri with L. hilgardii modified the consequences of exposure to air by maintaining higher microbial diversity, avoiding the dominance of a few bacteria, and preventing fungi from having a detrimental effect on silage quality.

Yeasts and Bacterial Consortia from Kefir Grains Are Effective Biocontrol Agents of Postharvest Diseases of Fruits

Fungal pathogens in fruits and vegetables cause significant losses during handling, transportation, and storage. Biological control with microbial antagonists replacing the use of chemical fungicides is a major approach in postharvest disease control, and several products based on single antagonists have been developed but have limitations related to reduced and inconsistent performance under commercial conditions. One possible approach to enhance the biocontrol efficacy is to broaden the spectrum of the antagonistic action by employing compatible microbial consortia. Here, we explore commercial kefir grains, a natural probiotic microbial consortium, by culture-dependent and metagenomic approaches and observed a rich diversity of co-existing yeasts and bacterial population. We report effective inhibition of the postharvest pathogen Penicillium expansum on apple by using the grains in its fresh commercial and milk-activated forms. We observed few candidate bacteria and yeasts from the kefir grains that grew together over successive enrichment cycles, and these mixed fermentation cultures showed enhanced biocontrol activities as compared to the fresh commercial or milk-activated grains. We also report several individual species of bacteria and yeasts with biocontrol activities against Penicillium rots on apple and grapefruit. These species with antagonistic properties could be further exploited to develop a synthetic consortium to achieve enhanced antagonistic effects against a wide range of postharvest pathogens.