Isolation, identification and screening of yeasts towards their ability to assimilate biodiesel-derived crude glycerol: microbial production of polyols, endopolysaccharides and lipid.

AIMS: To assess the ability of various newly isolated or belonging in official collections yeast strains to convert biodiesel-derived glycerol (Gly) into added-value compounds. METHODS AND RESULTS: Ten newly isolated yeast strains belonging to Debaryomyces sp., Naganishia uzbekistanensis, Rhodotorula sp. and Yarrowia lipolytica, isolated from fishes, metabolized Gly under nitrogen limitation. The aim of the study was to identify potential newly isolated microbial candidates that could produce single-cell oil (SCO), endopolysaccharides and polyols when these micro-organisms were grown on biodiesel-derived Gly. As controls producing SCO and endopolysaccharides were the strains Rhodotorula glutinis NRRL YB-252 and Cryptococcus curvatus NRRL Y-1511. At initial Gly (Gly0 ) ≈40 g l-1 , most strains presented remarkable dry cell weight (DCW) production, whereas Y. lipolytica and Debaryomyces sp. produced non-negligible quantities of mannitol and arabitol (Ara). Five strains were further cultivated at increasing Gly0 concentrations. Rhodotorula glutinis NRRL YB-252 produced 7·2 g l-1 of lipid (lipid in DCW value ≈38% w/w), whereas Debaryomyces sp. FMCC Y69 in batch-bioreactor experiment with Gly0 ≈80 g l-1 , produced 30-33 g l-1 of DCW and ~30 g l-1 of Ara. At shake-flasks with Gly0 ≈125 g l-1 , Ara of ~48 g l-1 (conversion yield of polyol on Gly consumed ≈0·62 g g-1 ) was achieved. Cellular lipids of all yeasts contained in variable concentrations oleic, palmitic, stearic and linoleic acids. CONCLUSIONS: Newly isolated, food-derived and non-previously studied yeast isolates converted biodiesel-derived Gly into several added-value metabolites. SIGNIFICANCE AND IMPACT OF THE STUDY: Alternative ways of crude Gly valorization through yeast fermentations were provided and added-value compounds were synthesized.

Yeast heterogeneity during spontaneous fermentation of black Conservolea olives in different brine solutions.

AIMS: To assess the yeast community structure and dynamics during Greek-style processing of natural black Conservolea olives in different brine solutions. METHODS AND RESULTS: Black olives were subjected to spontaneous fermentation in 6% (w/v) NaCl brine solution or brine supplemented with (i) 0.5% (w/v) glucose, (ii) 0.2% (v/v) lactic acid and (iii) both glucose and lactic acid. Yeast species diversity was evaluated at the early (2 days), middle (17 days) and final (35 days) stages of fermentation by restriction fragment length polymorphism and sequence analyses of the 5.8S internal transcribed spacer and the D1/D2 ribosomal DNA (rDNA) regions of isolates. Analysis revealed a relatively broad range of biodiversity composed of 10 genera and 17 species. In all treatments, yeasts were the main micro-organisms involved in fermentation together with lactic acid bacteria that coexisted throughout the processes. Metschnikowia pulcherrima was the dominant yeast species at the onset of fermentation, followed by Debaryomyces hansenii and Aureobasidium pullulans. Species heterogeneity changed as fermentations proceeded and Pichia membranifaciens along with Pichia anomala evolved as the main yeasts of olive elaboration, prevailing at 17 and 35 days of the process. Molecular techniques allowed for the identification of five yeast species, namely A. pullulans, Candida sp., Candida silvae, Cystofilobasidium capitatum and M. pulcherrima, which have not been reported previously in black olive fermentation. CONCLUSIONS: By using molecular techniques, a rich yeast community was identified from Conservolea black olive fermentations. Metschnikowia pulcherrima was reported for the first time to dominate in different brines at the onset of fermentation, whereas Pichia anomala and P. membranifaciens evolved during the course. The addition of glucose and/or lactic acid perturbed yeast succession and dominance during fermentation. SIGNIFICANCE AND IMPACT OF THE STUDY: Yeasts have an important role in black olive fermentation and contribute to the development of the organoleptic characteristics of the final product. At the same time, certain species can cause significant spoilage. The present study adds to a better knowledge of yeast communities residing in olive fermentations towards a well-controlled process with minimization of product's losses.

Isolation of culturable yeasts from market wines and evaluation of the 5.8S-ITS rDNA sequence analysis for identification purposes.

AIMS: To test the possibility that wines available in the marketplace may contain culturable yeasts and to evaluate the 5.8S-ITS rDNA sequence analysis as adequate means for the identification of isolates. METHODS AND RESULTS: As a case study, typical Greek wines were surveyed. Sequence analysis of the 5.8S-ITS rDNA was tested for its robustness in species or strain identification. Sixteen isolates could be assigned into the species Brettanomyces bruxellensis, Saccharomyces cerevisiae and Rhodotorula pinicola, whereas four isolates could not be safely identified. B. bruxellensis was the dominant species present in house wines, while non-Saccharomyces sp. were viable in aged wines of high alcohol content. CONCLUSIONS: Yeast population depends on postfermentation procedures or storage conditions. Although 5.8S-ITS rDNA sequence analysis is generally a rapid method to identify wine yeast isolates at the species level, or even below that, it may not be sufficient for some genera. SIGNIFICANCE AND IMPACT OF THE STUDY: This is the first report to show that commercial wines may possess diverse and potentially harmful yeast populations. The knowledge of yeasts able to reside in this niche environment is essential towards integrated quality assurance programmes. For selected species, the 5.8S-ITS rDNA sequence analysis is a rapid and accurate means.