Isolation, identification and selection of antagonistic yeast against Alternaria alternata infection and tenuazonic acid production in wine grapes from Argentina

Recent advances in biocontrol and other alternative strategies for the management of postharvest decay in table grapes

During postharvest, table grapes are often spoiled by molds. Aspergillus sp., Alternaria sp., Botrytis sp., Cladosporium sp. and Penicillium sp. are different mold genera frequently related to table grape rot. Fungal spoilage affects nutritional value and organoleptic properties while also producing health hazards, such as mycotoxins. Traditionally, synthetic fungicides have been employed to control fungal diseases. However, possible negative effects on health and the environment are a serious concern for consumers and government entities. This review summarized data on innovative strategies proposed to diminish postharvest losses and extend table grape shelf life. Among physical, chemical, and biological strategies, either alone or in combination, the integrated management of fungal diseases is a sustainable alternative to synthetic fungicides. However, to date, only a few alternative technologies have succeeded on a commercial scale. Recent research aimed at increasing the competitiveness of alternative technologies has led to the development of integrated management strategies to prevent postharvest decay and increase the safety and quality of table grapes.

Biocontrol of Alternaria alternata in cold-stored table grapes using psychrotrophic yeasts and bioactive compounds of natural sources

Alternaria alternata is a common fungal pathogen causing postharvest decay in table grapes. This study addressed the potential of autochthonous yeasts and bioactive compounds of natural sources to act as biocontrol agents (BCAs) against A. alternata in cold-stored table grapes. With this purpose, 19 yeast capable of growing at 0-1 °C were isolated from the surface of Red Globe table grapes. These isolates, along with the pre-isolated strain Metschnikowia pulcherrima RCM2, were evaluated as BCAs in wounded berries. From these results, six yeast isolates were pre-selected to be combined with bioactive compounds of natural sources, like phenolic compounds (PCs) of side streams of wine industry, including bunch stem extract (BSE) (5-25 %), and cane extract (CE) (5-25 %), and functional polysaccharides from shrimp waste such as chitosan (CH) (0.5 %). Then, the biocontrol efficacy of combined treatments beyond individual ones was compared. The results revealed that 4 yeast isolates, namely M. pulcherrima RCM2 and ULA146, and Aureobasidium pullulans FUL14 and FUL18, were the most effective. However, when combined with the natural bioactive compounds, their efficacy against A. alternata did not increase significantly. Notably, ULA146 and FUL18 demonstrated a biocontrol efficacy of 36-37 %, comparable to that of the treatment with commercial doses of SO2, which only showed a 27 % reduction in the lesion diameter. These findings highlight the potential of using psychrotrophic yeasts as BCAs against A. alternata in cold-stored table grapes. Combining these yeast strains with BSE, CE and CH did not increase BCAs efficacy against this pathogen at the concentrations tested. The development of effective biocontrol strategies for A. alternata could contribute to reducing reliance on chemically synthesized fungicides, promoting sustainable practices, aiming to improve the quality and safety of cold-stored table grapes.

Exploring future applications of the apiculate yeast Hanseniaspora

As a metaphor, lemons get a bad rap; however the proverb 'if life gives you lemons, make lemonade' is often used in a motivational context. The same could be said of Hanseniaspora in winemaking. Despite its predominance in vineyards and grape must, this lemon-shaped yeast is underappreciated in terms of its contribution to the overall sensory profile of fine wine. Species belonging to this apiculate yeast are known for being common isolates not just on grape berries, but on many other fruits. They play a critical role in the early stages of a fermentation and can influence the quality of the final product. Their deliberate addition within mixed-culture fermentations shows promise in adding to the complexity of a wine and thus provide sensorial benefits. Hanseniaspora species are also key participants in the fermentations of a variety of other foodstuffs ranging from chocolate to apple cider. Outside of their role in fermentation, Hanseniaspora species have attractive biotechnological possibilities as revealed through studies on biocontrol potential, use as a whole-cell biocatalyst and important interactions with Drosophila flies. The growing amount of 'omics data on Hanseniaspora is revealing interesting features of the genus that sets it apart from the other Ascomycetes. This review collates the fields of research conducted on this apiculate yeast genus.

Exploring yeast-based microbial interactions: The next frontier in postharvest biocontrol

Fresh fruits and vegetables are susceptible to a large variety of spoilage agents before and after harvest. Among these, fungi are mostly responsible for the microbiological deteriorations that lead to economically significant losses of fresh produce. Today, synthetic fungicides represent the first approach for controlling postharvest spoilage in fruits and vegetables worldwide. However, the emergence of fungicide-resistant pathogen biotypes and the increasing awareness of consumers toward the health implications of hazardous chemicals imposed an urgent need to reduce the use of synthetic fungicides in the food supply; this phenomenon strengthened the search for alternative biocontrol strategies that are more effective, safer, nontoxic, low-residue, environment friendly, and cost-effective. In the last decade, biocontrol with antagonistic yeasts became a promising strategy to reduce chemical compounds during fruit and vegetable postharvest, and several yeast-based biocontrol products have been commercialized. Biocontrol is a multipartite system that includes different microbial groups (spoilage mold, yeast, bacteria, and nonspoilage resident microorganisms), host fruit, vegetables, or plants, and the environment. The majority of biocontrol studies focused on yeast-mold mechanisms, with little consideration for yeast-bacteria and yeast-yeast interactions. The current review focused mainly on the unexplored yeast-based interactions and the mechanisms of actions in biocontrol systems as well as on the importance and advantages of using yeasts as biocontrol agents, improving antagonist efficiency, the commercialization process and associated challenges, and future perspectives.

Mosquito sex and mycobiota contribute to fructose metabolism in the Asian tiger mosquito Aedes albopictus

BACKGROUND

Plant floral nectars contain natural sugars such as fructose, which are a primary energy resource for adult mosquitoes. Despite the importance of carbohydrates for mosquito metabolism, a limited knowledge is available about the pathways involved in sugar assimilation by mosquitoes and their associated microbiota. To this end, we used 13C-metabolomic and stable isotope probing approaches coupled to high-throughput sequencing to reveal fructose-related mosquito metabolic pathways and the dynamics of the active gut microbiota following fructose ingestion.

RESULTS

Our results revealed significant differences in metabolic pathways between males and females, highlighting different modes of central carbon metabolism regulation. Competitive and synergistic interactions of diverse fungal taxa were identified within the active mycobiota following fructose ingestion. In addition, we identified potential cross-feeding interactions between this. Interestingly, there is a strong correlation between several active fungal taxa and the presence of fructose-derived metabolites.

CONCLUSIONS

Altogether, our results provide novel insights into mosquito carbohydrate metabolism and demonstrate that dietary fructose as it relates to mosquito sex is an important determinant of mosquito metabolism; our results also further highlight the key role of active mycobiota interactions in regulating the process of fructose assimilation in mosquitoes. This study opens new avenues for future research on mosquito-microbiota trophic interactions related to plant nectar-derived sugars. Video abstract.

Bioprotection strategies in winemaking

Worldwide the interest for biological control of food spoilage microorganisms has significantly increased over the last decade. Wine makes no exception to this trend, as consumer demands for wines free of preservatives that are considered negative for human health, increase. Biological control during wine fermentation aims at producing high quality wines, while minimizing, or even eliminating, the use of chemical additives. Its success lies in the inoculation of microorganisms to prevent, inhibit or kill undesired microbes, therefore maintaining wine spoilage at the lowest level. The food industry already makes use of this practice, with dedicated commercial microbes already on the market. In winemaking, there are commercial microbes currently under investigation, particularly with the aim to reduce or replace the use of sulphur dioxide. In this review, the potential of wine yeasts and lactic acid bacteria as bioprotection agents and their mechanisms of action during wine fermentation are presented.

Isolation and Identification of Wild Yeast from Malaysian Grapevine and Evaluation of Their Potential Antimicrobial Activity against Grapevine Fungal Pathogens

Pathogenic fungi belonging to the genera Botrytis, Phaeomoniella, Fusarium, Alternaria and Aspergillus are responsible for vines diseases that affect the growth, grapevine yield and organoleptic quality. Among innovative strategies for in-field plant disease control, one of the most promising is represented by biocontrol agents, including wild epiphytic yeast strains of grapevine berries. Twenty wild yeast, isolated and molecularly identified from three different Malaysian regions (Perlis, Perak and Pahang), were evaluated in a preliminary screening test on agar to select isolates with inhibition against Botrytis cinerea. On the basis of the results, nine yeasts belonging to genera Hanseniaspora, Starmerella, Metschnikowia, Candida were selected and then tested against five grape berry pathogens: Aspergillus carbonarius, Aspergillus ochraceus, Fusarium oxysporum, Alternaria alternata and Phaeomoniella chlamydospora.Starmerella bacillaris FE08.05 and Metschnikowia pulcherrima GP8 and Hanseniaspora uvarum GM19 showed the highest effect on inhibiting mycelial growth, which ranged between 15.1 and 4.3 mm for the inhibition ring. The quantitative analysis of the volatile organic compound profiles highlighted the presence of isoamyl and phenylethyl alcohols and an overall higher presence of low-chain fatty acids and volatile ethyl esters. The results of this study suggest that antagonist yeasts, potentially effective for the biological control of pathogenic moulds, can be found among the epiphytic microbiota associated with grape berries.

Diffusible Compounds Produced by Hanseniaspora osmophila and Gluconobacter cerinus Help to Control the Causal Agents of Gray Rot and Summer Bunch Rot of Table Grapes

Gray and summer bunch rot are important diseases of table grapes due to the high economic and environmental cost of their control with synthetic fungicides. The ability to produce antifungal compounds against the causal agents Botrytis, Aspergillus, Penicillium, and Rhizopus of two microorganisms isolated from table grapes and identified as Hanseniaspora osmophila and Gluconobacter cerinus was evaluated. In dual cultures, both biocontrol agents (together and separately) inhibited in vitro mycelial growth of these pathogens. To identify the compounds responsible for the inhibitory effect, extractions were carried out with organic solvents from biocontrol agents separately. Through dual cultures with pathogens and pure extracts, only the hexane extract from H. osmophila showed an inhibitory effect against Botrytis cinerea. To further identify these compounds, the direct bioautography technique was used. This technique made it possible to determine the band displaying antifungal activity at Rf = 0.05–0.2. The compounds present in this band were identified by GC-MS and compared to the NIST library. The most abundant compounds, not previously reported, corresponded to alkanes, ketones, alcohols, and terpenoids. H. osmophila and G. cerinus have the potential to control the causal agents of gray and summer bunch rot of table grapes.

Genetic, Physiological, and Industrial Aspects of the Fructophilic Non-Saccharomyces Yeast Species, Starmerella bacillaris

Starmerella bacillaris (synonym Candida zemplinina) is a non-Saccharomyces yeast species, frequently found in enological ecosystems. Peculiar aspects of the genetics and metabolism of this yeast species, as well as potential industrial applications of isolated indigenous S. bacillaris strains worldwide, have recently been explored. In this review, we summarize relevant observations from studies conducted on standard laboratory and indigenous isolated S. bacillaris strains.

Development of a chemiluminescence immunoassay for detection of tenuazonic acid mycotoxin in fruit juices with a specific camel polyclonal antibody

The natural mycotoxin tenuazonic acid (TeA) in foods is identified as the most toxic mycotoxin among the over 70 kinds of secondary toxic metabolites produced by Alternaria alternata. Some hapten-antibody-mediated immunoassays have been developed for TeA detection in food samples, but these methods show unsatisfactory sensitivity and specificity. In this study, a rationally designed hapten for TeA mycotoxin generated with computer-assisted modeling was prepared to produce a highly specific camel polyclonal antibody, and an indirect competitive chemiluminescence enzyme immunoassay (icCLEIA) was established with a limit of detection of 0.2 ng mL-1 under optimized conditions. The cross-reactivity results showed that several analogs and some common mycotoxins had negligible recognition by the anti-TeA polyclonal antibody. The average recoveries spiked in fruit juices were determined to be 92.7% with an acceptable coefficient of variation, and good correlations between icCLEIA and liquid chromatography tandem mass spectrometry (LC-MS/MS) results were obtained in spiked samples. This developed icCLEIA for TeA detection with significantly improved sensitivity and satisfactory specificity is a promising alternative for environmental monitoring and food safety.

Impact of antagonistic yeasts from wine grapes on growth and mycotoxin production by Alternaria alternata

AIMS

Alternaria alternata is a major contaminant of wine grapes, meaning a health risk for wine consumers due to the accumulation of toxic metabolites. To develop a successful biofungicide, the effectiveness of epiphytic wine grape yeasts against A. alternata growth and toxin production was assessed in vitro under temperature and a_W conditions that simulate those present in the field.

METHODS AND RESULTS

The effect of 14 antagonistic yeasts was evaluated on growth and alternariol (AOH), alternariol monomethyl ether (AME) and tenuazonic acid (TA) production by three A. alternata strains in a synthetic medium with composition similar to grape (SN) at three temperatures (15, 25 and 30°C). All Metschnikowia sp. yeast strains evaluated completely prevented A. alternata growth and mycotoxin production at all temperatures in SN medium. Meanwhile, the growth inhibition exerted by Starmerella bacillaris yeast strains was higher at 30°C, followed by 25 and 15°C, being able to show a stimulating or inhibiting effect. Hanseniaspora uvarum yeast strains showed a growth promoting activity higher at 15°C, followed by 25 and 30°C. Even at conditions where A. alternata growth was stimulated by the S. bacillaris and H. uvarum yeasts, high inhibitions of mycotoxin production (AOH, AME and TA) were observed, indicating a complex interaction between growth and mycotoxin production.

CONCLUSION

There is a significant influence of temperature on the effectiveness of biocontrol against A. alternata growth and mycotoxin production. Metschnikowia sp. strains are good candidates to compose a biofungicide against A. alternata.

SIGNIFICANCE AND IMPACT OF THE STUDY

Among the different antagonistic yeasts evaluated, only Metschnikowia sp. strains were equally effective reducing A. alternata growth and mycotoxin at different temperatures underlining the importance of considering environmental factors in the selection of the antagonists.

Effect of Debaryomyces hansenii and the antifungal PgAFP protein on Alternaria spp. growth, toxin production, and RHO1 gene expression in a tomato-based medium

Tomato fruit is susceptible to Alternaria spp. spoilage, which poses a health risk due to their mycotoxin production. Biopreservation relies on the use of whole microorganisms or their metabolites to manage spoilage microorganisms including filamentous fungi. However, the use of treatments at fungistatic level might activate intracellular pathways, which can cause an increment in mycotoxin accumulation. The objective of this work was to evaluate the effect of two strains of Debaryomyces hansenii and the antifungal protein PgAFP at 10 and 40 μg/mL. Both growth and production of two of the most common mycotoxins (tenuazonic acid and alternariol monomethyl ether) by Alternaria tenuissima sp.-grp. and Alternaria arborescens sp.-grp. on a tomato-based matrix, were analysed at 12 °C. Additionally, the impact of these biocontrol agents on the stress-related RHO1 gene expression was assessed. All treatments reduced mycotoxin accumulation (from 27 to 92% of inhibition). Their mode of action against Alternaria spp. in tomato seems unrelated to damages to fungal cell wall integrity at the genomic level. Therefore, the two D. hansenii strains (CECT 10352 and CECT 10353) and the antifungal protein PgAFP at 10 μg/mL are suggested as biocontrol strategies in tomato fruit at postharvest stage.

Control of Penicillium glabrum by Indigenous Antagonistic Yeast from Vineyards

Biocontrol is one of the most promising alternatives to synthetic fungicides for food preservation. Botrytis cinerea, Alternaria alternata, and Aspergillus section Nigri are the most concerning pathogens for grape development. However, frequently, other species, such as Penicillium glabrum in this study, are predominant in spoiled bunches. In this work, 54 native yeasts from vineyards were screened by direct confrontation in potato dextrose agar plates as antagonists against P. glabrum. Isolates of Pichia terricola, Aureobasidium pullulans, and Zygoascus meyerae were selected for their antagonist activity in vitro, plus isolates of Pichia kudriavzevii, Hormonema viticola, and Hanseniaspora uvarum were used as negative controls. However, in vivo, confrontations in wounded grapes showed disagreement with direct confrontation in vitro. P. terricola, P. kudriavzevii, H. viticola, Z. meyerae, and H. uvarum significantly reduced the incidence of P. glabrum on grapes. Nevertheless, P. terricola, H. viticola, and H. uvarum themselves spoiled the wounded grapes. Inhibitions were associated with different mechanisms such as the production of volatile organic compounds (VOCs), lytic enzymes, biofilm formation, and competition for nutrients. The isolates of P. kudriavzevii L18 (a producer of antifungal VOCs which completely inhibited the incidence of P. glabrum) and Z. meyerae L29 (with pectinase, chitinase and β-glucanase activity and biofilm formation which reduced 70% of the incidence of P. glabrum) are proposed as suitable biocontrol agents against P. glabrum.

Biocontrol efficiency of Meyerozyma guilliermondii Y-1 against apple postharvest decay caused by Botryosphaeria dothidea and the possible mechanisms of action

Apple ring rot, caused by Botryosphaeria dothidea, is one of the important diseases in China. This pathogen infects branches and fruit and also results in fruit decay during storage. Biocontrol agents have been proposed to reduce apple decays during storage and are considered as a promising alternative strategy to traditional chemical treatment. In this study, Meyerozyma guilliermondii Y-1, isolated from healthy grape fruit, was firstly evaluated for its biocontrol efficiency against B. dothidea in postharvest apple fruit, and the possible mechanisms were investigated. The results revealed that M. guilliermondii Y-1 treatment effectively reduced apple ring rot caused by B. dothidea in vivo. The disease incidence and lesion diameter were reduced by 32.22% and 57.51% compared with those of control fruit. Furthermore, the use of filtrate and autoclaved culture of M. guilliermondii Y-1 also showed a certain degree of control efficiency against fruit ring rot. M. guilliermondii Y-1 significantly inhibited the mycelial growth and spore generation of B. dothidea in vitro and exhibited an obvious ability to colonize in apple fruit wounds and surface at 25 °C or 4 °C. In addition, M. guilliermondii Y-1 treatment significantly enhanced the activities of catalase (CAT), superoxide dismutase (SOD), peroxidase (POD), phenylalanine ammonialyase (PAL), and polyphenoloxidase (PPO), promoted the total phenolics content, and alleviated lipid peroxidation in apple fruit. As expected, we found that the expression of four pathogenesis-related proteins genes (MdPR1, MdPR5, MdGLU, and MdCHI) was remarkably increased by M. guilliermondii Y-1 treatment. Our data together suggest that M. guilliermondii Y-1 is a potential biocontrol agent against B. dothidea postharvest infection in apple fruit, partially through inhibiting mycelial growth and spore germination of B. dothidea, competing for space and nutrient with pathogen, and inducing resistance in apple fruit by stimulating a series of defense responses.

Effects of ε-poly-l-lysine on vegetative growth, pathogenicity and gene expression of Alternaria alternata infecting Nicotiana tabacum

Microbial secondary metabolites produced by Streptomyces are applied to control plant diseases. ε-poly-l-lysine (ε-PL) is a non-toxic food preservative, but the potential application of ε-PL as a microbial fungicide in agriculture has rarely been reported. In this study, Alternaria alternata (A. alternata) was used to reveal the effect and mode of action for ε-PL on the plant pathogenic fungi. The results showed that ε-PL effectively inhibited necrotic-lesion development caused by A. alternata on tobacco. Mycelial growth was also significantly inhibited in vitro by 100 μg/ml ε-PL using in vitro analysis. Moreover, 25 μg/ml ε-PL inhibited spore germination and induced abnormal morphological development of A. alternata hyphae. To clarify the molecular-genetic antifungal mechanisms, we selected several crucial genes involved in the development and pathogenesis of A. alternata and studied their expression regulated by ε-PL. Results of real-time quantitative PCR showed that a mycelium morphology and pathogenic process related cyclic adenosine monophosphate protein (cAMP) dependent protein kinase A (PKA), Alternaria alternata cAMP-dependent protein kinase catalytic subunit (AAPK1) and the early infection-related glyceraldehyde-3-phosphate dehydrogenase (GAPDH) were down-regulated after ε-PL treatment. The results provide novel insights for the application of ε-PL in the control of plant diseases caused by A. alternata.