Antifungal activity of non-conventional yeasts against Botrytis cinerea and non-Botrytis grape bunch rot fungi

Unravelling the transcriptomic dynamics of Hyphopichia pseudoburtonii in co-culture with Botrytis cinerea

Hyphopichia pseudoburtonii, is emerging as a potential biocontrol agent against various phytopathogens. These traits have been attributed to the production of various antifungal compounds in the presence of target pathogens. However, the broad molecular mechanisms involved in the antifungal activity are not yet understood. This study employed RNA sequencing to assess the temporal changes in H. pseudoburtonii Y963 gene expression patterns when co-cultivated with Botrytis cinerea. Genes differentially expressed in H. pseudoburtonii in co-culture with B. cinerea, compared to the monoculture were evaluated after 24, 48, and 120 h of growth. Up-regulation of genes encoding major core histones (H2A, H3, H4) and ribosomes in the first 24 h suggested an abundance of cells in the S phase of the cell cycle. At 48 h, the genes up-regulated highlight mitotic cell cycle activity and induction of filamentous growth, while in later stages, up-regulation of genes encoding high affinity transporters of sugars, copper and iron, as well as those involved in the retention and utilization of siderophore-iron was evident. Altogether, the data allude to competition for space and nutrients as key mechanisms activated in H. pseudoburtonii in the presence of B. cinerea. This research offers new insights into H. pseudoburtonii transcriptomic response to B. cinerea and illuminates the adaptive strategies and molecular mechanisms behind its antifungal activity.

The Use of Specific Non-Saccharomyces Yeasts as Sustainable Biocontrol Solutions Against Botrytis cinerea on Apples and Strawberries

Apples and strawberries hold significant commercial and nutritional value but face pre- and post-harvest spoilage due to infections by Botrytis cinerea. While spoilage is conventionally managed using synthetic chemicals, there is a growing interest in utilising yeasts as biological control agents. This study aimed to assess the antifungal potential of non-Saccharomyces yeasts Suhomyces pyralidae, Meyerozyma guilliermondii, Pichia kluyveri, Zygoascus hellenicus, and Aureobasidium melanogenum against three B. cinerea strains (B05.10, IWBT-FF1, and PPRI 30807) on agar plates and in post-harvest trials on apples and strawberries. Aureobasidium melanogenum exhibited a broad range of extracellular enzyme production and inhibition rates of 55%, 52%, and 40% against the strains. In volatile organic compound (VOC) assays, P. kluyveri and S. pyralidae achieved 79% and 56% inhibition, respectively, with VOCs like isobutanol, isoamyl alcohol, 2-phenylethanol, isoamyl acetate, and 2-phenethyl acetate identified. In post-harvest trials, S. pyralidae was most effective on apples, with inhibition rates up to of 64%. The commercial fungicide Captan and S. pyralidae and P. kluyveri achieved 100% inhibition against the B. cinerea strains B05.10 and IWBT-FF1 on strawberries. These findings highlight the potential of the selected yeast species as biological control agents against B. cinerea, warranting further research into their application in commercial fruit protection.

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.

Identification of antagonistic yeasts as potential biocontrol agents: Diverse criteria and strategies

Plant pathogenic and food spoilage microorganisms cause serious losses in crop production and severe damage during food manufacturing, transportation and storage. Synthetic antimicrobial agents are commonly used to control their propagation and harmful activities. However, the recent trend is shifting from chemicals towards safer and more eco-friendly alternatives. The use of antagonistic microorganisms as biological antimicrobial agents is becoming popular throughout the world to replace chemical agents. High numbers of microorganisms have turned out to exert adverse/inhibitory effects on other microorganisms including pathogens and spoiling strains. However, most of them are only active under laboratory conditions and their activity is sensitive to environmental changes. Only a small number of them can be used to manufacture biological protective products on an industrial scale. Therefore, there is a great need to identify additional antagonists. Yeasts have come to the forefront of attention because antimicrobial antagonism is fairly widespread among them. In the recent years, numerous excellent review articles covered various aspects of the phenomenon of antimicrobial antagonism of yeasts. However, none of them dealt with how antagonistic yeasts can be sought and identified, despite the high number and diverse efficiency of screening and identification procedures. As researchers working in different laboratories use different criteria and different experimental set-ups, a yeast strain found antagonistic in one laboratory may prove to be non-antagonistic in another laboratory. This review aims to provide a comprehensive and partially critical overview of the wide diversity of identification criteria and procedures to help researchers choose appropriate screening and identification strategies.

From bioprotective effects to diversification of wine aroma: Expanding the knowledge on Metschnikowia pulcherrima oenological potential

Microbial diseases are of major concern in vitiviniculture as they cause grape losses and wine alterations, but the prevention with chemical substances represents a risk to human health and agricultural ecosystem. A promising alternative is the biocontrol and bioprotection activity of non-Saccharomyces yeasts, such as Metschnikowia pulcherrima, which also presents positive oenological traits when used in multistarter fermentations. The aim of this study was to assess the impact of a selected M. pulcherrima strain in the post-harvest withering and vinification of Garganega grapes to produce the sweet 'passito' wine Recioto di Gambellara DOCG (Italy). M. pulcherrima was firstly inoculated on grape at the beginning of the withering process, and afterwards in must for multistarter sequential microfermentation trials with Saccharomyces cerevisiae. Microbiological, chemical, and sensory analyses were carried out to monitor the vinification of treated and control grapes. Grape bunches during withering were a suitable environment for the colonization by M. pulcherrima, which effectively prevented growth of molds. Differences in grape must composition were observed, and the diverse inoculation strategies caused noticeable variations of fermentation kinetics, main oenological parameters, wine aroma profile, and sensory perception. M. pulcherrima proved effective to protect grapes against fungal infections during withering and contribute to alcoholic fermentation generating wine with distinguished aromatic characteristics.

Towards unlocking the biocontrol potential of Pichia kudriavzevii for plant fungal diseases: in vitro and in vivo assessments with candidate secreted protein prediction

BACKGROUND

Plant fungal pathogens cause substantial economic losses through crop yield reduction and post-harvest storage losses. The utilization of biocontrol agents presents a sustainable strategy to manage plant diseases, reducing the reliance on hazardous chemical. Recently, Pichia kudriavzevii has emerged as a promising biocontrol agent because of its capacity to inhibit fungal growth, offering a potential solution for plant disease management.

RESULTS

Two novel Pichia kudriavzevii strains, Pk_EgyACGEB_O1 and Pk_EgyACGEB_O2, were isolated from olive brine samples. The microscopic characterization of the strains revealed similar structures. However, there were noticeable differences in their visual morphology. Based on their internal transcribed spacer (ITS) DNA sequences, Pk_EgyACGEB_O1 and Pk_EgyACGEB_O2 strains assigned by GenBank IDs MZ507552.1 and MZ507554.1 shared high sequence similarity (~ 99.8% and 99.5%) with P. kudriavzevii, respectively. Both strains were evaluated in vitro against plant pathogenic fungi. The strains revealed the ability to consistently inhibit fungal growth, with Pk_EgyACGEB_O2 showing higher effectiveness. In addition, both P. kudriavzevii strains effectively controlled grey mold disease caused by B. cinerea in golden delicious apples, suggesting their potential as sustainable and eco-friendly biocontrol agents for post-harvest diseases. Based on a comprehensive bioinformatics pipeline, candidate-secreted proteins responsible for the potent antifungal activity of P. kudriavzevii were identified. A total of 59 proteins were identified as common among the P. kudriavzevii CBS573, SD108, and SD129 strains. Approximately 23% of the secreted proteins in the P. kudriavzevii predicted secretome are hydrolases with various activities, including proteases, lipases, glycosidases, phosphatases, esterases, carboxypeptidases, or peptidases. In addition, a set of cell-wall-related proteins was identified, which might enhance the biocontrol activity of P. kudriavzevii by preserving the structure and integrity of the cell wall. A papain inhibitor was also identified and could potentially offer a supplementary defense against plant pathogens.

CONCLUSION

Our results revealed the biocontrol capabilities of P. kudriavzevii against plant pathogenic fungi. The research focused on screening novel strains for their ability to inhibit the growth of common pathogens, both in vitro and in vivo. This study shed light on how P. kudriavzevii interacts with fungal pathogens. The findings can help develop effective strategies for managing plant diseases.

Exploring the effects of the fermentation method on the quality of Lycium barbarum and Polygonatum cyrtonema compound wine based on LC-MS metabolomics

This study aimed to examine the effect of fermentation methods on the quality of Lycium barbarum and Polygonatum cyrtonema compound wine (LPW) by combining non-targeted metabolomic approaches with chemometrics and path profiling to determine the chemical and metabolic properties of LPW. The results demonstrated that SRA had higher leaching rates of total phenols and flavonoids, reaching 4.20 ± 0.10 v/v ethanol concentration. According to LC-MS non-targeting genomics, the metabolic profiles of LPW prepared by different mixtures of fermentation methods (Saccharomyces cerevisiae RW; Debaryomyces hansenii AS2.45) of yeast differed significantly. Amino acids, phenylpropanoids, flavonols, etc., were identified as the differential metabolites between different comparison groups. The pathways of tyrosine metabolism, biosynthesis of phenylpropanoids, and metabolism of 2-oxocarboxylic acids enriched 17 distinct metabolites. SRA stimulated the production of tyrosine and imparted a distinctive saucy aroma to the wine samples, providing a novel research concept for the microbial fermentation-based production of tyrosine.

Biocontrol potential of wine yeasts against four grape phytopathogenic fungi disclosed by time-course monitoring of inhibitory activities

Grapes' infection by phytopathogenic fungi may often lead to rot and impair the quality and safety of the final product. Due to the concerns associated with the extensive use of chemicals to control these fungi, including their toxicity for environment and human health, bio-based products are being highly preferred, as eco-friendlier and safer alternatives. Specifically, yeasts have shown to possess antagonistic activity against fungi, being promising for the formulation of new biocontrol products.In this work 397 wine yeasts, isolated from Portuguese wine regions, were studied for their biocontrol potential against common grapes phytopathogenic fungal genera: Aspergillus, Botrytis, Mucor and Penicillium. This set comprised strains affiliated to 32 species distributed among 20 genera. Time-course monitoring of mold growth was performed to assess the inhibitory activity resulting from either diffusible or volatile compounds produced by each yeast strain. All yeasts displayed antagonistic activity against at least one of the mold targets. Mucor was the most affected being strongly inhibited by 68% of the tested strains, followed by Botrytis (20%), Aspergillus (19%) and Penicillium (7%). More notably, the approach used allowed the detection of a wide array of yeast-induced mold response profiles encompassing, besides the decrease of mold growth, the inhibition or delay of spore germination and the complete arrest of mycelial extension, and even its stimulation at different phases. Each factor considered (taxonomic affiliation, mode of action and fungal target) as well as their interactions significantly affected the antagonistic activity of the yeast isolates. The highest inhibitions were mediated by volatile compounds. Total inhibition of Penicillium was achieved by a strain of Metschnikowia pulcherrima, while the best performing yeasts against Mucor, Aspergillus and Botrytis, belong to Lachancea thermotolerans, Hanseniaspora uvarum and Starmerella bacillaris, respectively. Notwithstanding the wide diversity of yeasts tested, only three strains were found to possess a broad spectrum of antagonistic activity, displaying strong or very strong inhibition against the four fungal targets tested. Our results confirm the potential of wine yeasts as biocontrol agents, while highlighting the need for the establishment of fit-for-purpose selection programs depending on the mold target, the timing, and the mode of application.