Studies toward the comprehension of fungal-macroalgae interaction in cold marine regions from a biotechnological perspective.

In marine ecosystems, macroalgae are the habitat for several microorganisms, fungi being among them. In the Antarctic benthic coastal ecosystem, macroalgae play a key role in organic matter cycling. In this study, 13 different macroalgae from Potter Cove and surrounding areas were sampled and 48 fungal isolates were obtained from six species, four Rhodophyta Ballia callitricha, Gigartina skottsbergii, Neuroglossum delesseriae and Palmaria decipiens, and two Phaeophyceae: Adenocystis utricularis and Ascoseira mirabilis. Fungal isolates mostly belonged to the Ascomycota phylum (Antarctomyces, Cadophora, Cladosporium, Penicillium, Phialocephala, and Pseudogymnoascus) and only one to the phylum Mucoromycota. Two of the isolates could not be identified to genus level, implying that Antarctica is a source of probable novel fungal taxa with enormous bioprospecting and biotechnological potential. 73% of the fungal isolates were moderate eurypsychrophilic (they grew at 5-25 °C), 12.5% were eurypsychrophilic and grew in the whole range, 12.5% of the isolates were narrow eurypsychrophilic (growth at 15-25 °C), and Mucoromycota AUe4 was classified as stenopsychrophilic as it grew at 5-15 °C. Organic extracts of seven macroalgae from which no fungal growth was obtained (three red algae Georgiella confluens, Gymnogongrus turquetii, Plocamium cartlagineum, and four brown algae Desmarestia anceps, D. Antarctica, Desmarestia menziesii, Himantothallus grandifolius) were tested against representative fungi of the genera isolated in this work. All extracts presented fungal inhibition, those from Plocamium cartilagineum and G. turquetii showed the best results, and for most of these macroalgae, this represents the first report of antifungal activity and constitute a promising source of compounds for future evaluation.

Use of yeasts from different environments for the control of Penicillium expansum on table grapes at storage temperature.

A wide range of fresh fruits and vegetables is attacked by Penicillium species causing diseases during their postharvest handling. Many of these species are psychrotrophic and they are able to cause food spoilage at refrigeration temperature as happens with table grapes. After the harvest, grape bunches are stored inside boxes with SO2 generator pads to reduce the contamination with fungal conidia. However, SO2 residues are dangerous to people allergic to sulfites and they negatively affect the quality of fresh fruit. Biological control of phytopathogens with microbial antagonists naturally present on fruit surfaces could be helpful against postharvest diseases. The present study aimed to select native yeasts isolated from fermentation microenvironments and the surface of refrigerated grapes for their use in the biological control of P. expansum on table grapes stored in cold rooms. Non-pathogenic and pathogenic Penicillium species were isolated, and the four most aggressive pathogen isolates were identified as Penicillium expansum. Twenty yeast isolates identified as Aureobasidium pullulans, Cryptococcus magnus, Metschnikowia pulcherrima and Rhodotorula glutinis presented positive antagonistic activity against Penicillium expansum; they controlled the development of at least one of the fungi, significantly reducing the disease incidence. The results showed that three antagonistic yeasts (M. pulcherrima 22, 36 and 43) reduced the disease incidence and severity of all 4 P. expansum isolates. It was also found that the fruit surface is not the only source for isolation of biological control agents. Microenvironments with different stress conditions could be a promising source to isolate antagonistic microorganisms.

Antifungal modes of action of Saccharomyces and other biocontrol yeasts against fungi isolated from sour and grey rots.

The aim of this study was to determine the putative modes of action of 59 viticultural yeasts (31 Saccharomyces and 28 non-Saccharomyces) that inhibited fungi isolated from sour and grey rot in grapes. Inhibition of fungal mycelial growth by metabolites, enzyme activities (laminarinases, chitinases), antifungal volatiles, competition for nutrients (siderophores, Niche Overlap Index (NOI)), inhibition of fungal spore germination and decreased germinal tube length and induction of resistance were assayed. Biofungicide yeasts were classified into "antifungal patterns", according to their mechanisms of action. Thirty isolates presented at least two of the mechanisms assayed. We propose that inhibition of fungal mycelial growth by metabolites, laminarinases, competition for nutrients, inhibition of fungal spore germination and decreased germinal tube length, and antifungal volatiles by Saccharomyces and non-Saccharomyces viticultural yeasts is used as putative biocontrol mechanisms against phytopathogenic fungi. Twenty-four different antifungal patterns were identified. Siderophore production (N)and a combination of siderophore production and NOI>0.92 (M)were the most frequent antifungal patterns observed in the biofungicide yeasts assayed. Elucidation of these mechanisms could be useful for optimization of an inoculum formulation, resulting in a more consistent control of grey and sour rot with Saccharomyces and non-Saccharomyces biocontrol yeasts.

Glycerol and arabitol production by an intergeneric hybrid, PB2, obtained by protoplast fusion between Saccharomyces cerevisiae and Torulaspora delbrueckii.

An intergeneric osmotolerant hybrid yeast, PB2, was used together with the parental strains to study glycerol and arabitol production in batch culture. This fusion product was previously obtained by protoplast fusion between Torulaspora delbrueckii and Saccharomyces cerevisiae. Polyols and biomass production were determined in batch culture under aerobic conditions. Under the conditions tested, using PB2 hybrid and both parental strains, the best results were obtained with the hybrid. Arabitol reached a final concentration of 70 g/l and glycerol was increased to up to 50 g/l.

Isolation and identification of xylitol-producing yeasts from agricultural residues.

Selected yeast strains isolated from corn silage and viticulture residues were screened for their capacities to convert D-xylose into xylitol A conventional TLC was adapted for easy determination of xylose and xylitol in the culture supernatant solutions. This technique is suitable for the first steps of a screening program to select xylitol-producing yeasts from natural environments. Candida tropicalis ASM III (NRRL Y-27290), isolated from corn silage, appears to be a promising strain for xylitol production with a high yield (0.88 g xylitol per g of xylose consumed).

Hybrids obtained by protoplast fusion with a salt-tolerant yeast.

An industrial strain of Saccharomyces cerevisiae was fused with an osmotolerant yeast, Debaryomyces hansenii, to obtain hybrids having increased tolerance to elevated salt concentrations. The hybrids were intermediate to parent species in production of ethanol and polyols.

[Effect of treatment with p-fluorophenylalanine on the mating capacity of industrial polyploid yeasts]. / Efecto del tratamiento con p-fluorfenilalanina sobre la capacidad de conjugar levaduras poliploides industriales.

Brewing yeast strains of the genus Saccharomyces uvarum (carlsbergensis) were grown on media containing p-fluorophenylalanine (p-FPA). After the treatment, non-sporulation colonies were selected, and these were mated with haploid strains of flocculent and amylolytic yeasts of the genus Saccharomyces. The selected hybrids, which carried the greater part of the parental genetic markers and produced asci containing 2,3 and 4 spores per ascus, were placed on sporulation medium. Some aspects of the probable action of p-FPA are discussed.

Efecto del tratamiento con p-fluorfenilalanina sobre la capacidad de conjugar levaduras poliploides industriales / [Effect of treatment with p-fluorophenylalanine on the mating capacity of industrial polyploid yeasts]

Brewing yeast strains of the genus Saccharomyces uvarum (carlsbergensis) were grown on media containing p-fluorophenylalanine (p-FPA). After the treatment, non-sporulation colonies were selected, and these were mated with haploid strains of flocculent and amylolytic yeasts of the genus Saccharomyces. The selected hybrids, which carried the greater part of the parental genetic markers and produced asci containing 2,3 and 4 spores per ascus, were placed on sporulation medium. Some aspects of the probable action of p-FPA are discussed.

Efecto del tratamiento con p-fluorfenilalanina sobre la capacidad de conjugar levaduras poliploides industriales. / [Effect of treatment with p-fluorophenylalanine on the mating capacity of industrial polyploid yeasts]

Brewing yeast strains of the genus Saccharomyces uvarum (carlsbergensis) were grown on media containing p-fluorophenylalanine (p-FPA). After the treatment, non-sporulation colonies were selected, and these were mated with haploid strains of flocculent and amylolytic yeasts of the genus Saccharomyces. The selected hybrids, which carried the greater part of the parental genetic markers and produced asci containing 2,3 and 4 spores per ascus, were placed on sporulation medium. Some aspects of the probable action of p-FPA are discussed.