The dissertation is devoted to the study of biodiversity and biological characteristics of the yeasts, isolated from the dairy products and the contents of the healthy centenarians’ distal intestine, as well as of their impact on opportunistic bacteria. The work also reveals the ecological aspects of the relationship between yeasts and various bacteria of the genus Pseudomonas spp in sense of aggregative behaviour of bacteria, including their mobility and biofilm formation.
The identification of 93 newly isolated yeasts showed the significant dominance yeasts of the genus Candida (34 %) and Debaryomyces (25 %) in the gastrointestinal tract samples of Hutsul centenarians. In dairy products overall, the most numerous were yeasts of the genera Kluyveromyces (26 %), Candida (16 %) and Saccharomyces (15%). The dominant yeasts genera in guslyanka were Kluyveromyces (29 %) and Saccharomyces (26 %). The genus Kluyveromyces (38 %) was characteristic for sour-cream isolates. Among the biological characteristics, all tested yeasts strains were found to be susceptible to nystatin.
According to The Principal Component Analysis (PCA), the First Principal Component (PC1) was associated with the ability of yeasts to inhibit growth of many bacteria, and the Second Principal Component (PC2) was determined by the high quantitative indices of antagonism to the strains B. cereus UCM B-911, E. coli UCM B-906 and P. aeruginosaUCM B-900. The best results for PC1 were demonstrated by the yeasts S. uvarum FF20 and Y. lipolytica FF21 and FF24 isolated from cheese, which inhibited all eight tested bacteria growth. Isolated from GIT of Abkhaz centenarians in 80s, collection strains S. cerevisiae 11k and 14k showed the highest quantitative antagonism rates for PC2, and had the largest inhibition zones for B. cereus UCM B-911 and E. сoli UCM B-906 (50-55 mm).
It was found that the yeasts from a dairy product guslyanka started to develop antagonistic activity at lower pH values (5.0-5.5) than the yeasts from GIT (6.0), and had maximal antagonistic activity under more acidic conditions compared to the strains from GIT, pH 5.5 and 6.0, respectively.
A large variety of yeast effects on the aggregative behaviour of the pseudomonads was established, which may include both stimulating and inhibitory effects, and is dependent on the combination of pseudomonad and yeast strains, as well as on the dose of the yeast supernatant. Overall, for all studied supernatant concentrations (17-100 % v/v), K. marxianus FF8 had the greatest influence on the characteristics of pseudomonads’ biofilm formation, inhibiting the bacterial growth and aggregative behaviour.
The relationship between mobility processes and biofilm characteristics of the model pseudomonads with different types of biofilms at 24 hours of cultivation under impact of a 50 % concentration of the yeast supernatant of S. cerevisiae 11k, S. uvarum FF20 and K. marxianus FF8 was tested using multivariate analysis.
According to the cluster analysis of variables, the highest degree of the similarity (73 %) was found for the twitching mobility and the bacterial biofilm strength, which were also characterized by the high negative values of the Second Principal Component (PC2) coefficients for PCA. Swimming was more associated with the cells attachment to glass, as evidenced by the similarity of 57 % and the values of PC1 coefficients.
Key words: yeasts, dairy products, gastrointestinal tract (GIT), centenarians, biodiversity, ITS rRNA, antagonistic activity against bacteria, Pseudomonas spp., aggregation behavior, biofilm formation, swimming and twitching moving.
