DETERMINATION OF THE MICROBIAL PROFILE OF COMPRESSED BAKER'S YEAST AND STUDYING ITS SYMBIOTIC INTERACTIONS

Baker's yeast; Saccharomyces cerevisiae; is one of the oldest products of industrial fermentation used for bread manufacturing which is a staple food worldwide. Three different brands of compressed baker's yeast were examinedfor their microbial profile. The mean totalyeast viablecounts ranged from 10.26± 0.31 to 10.39± 0.42 log CFU/g with no significant difference between brands. The bacterial counts were determined on nutrient agar, actidione agar and MRS agar media and showed that it ranged from 7.44± 0.58 to 8.24± 0.51 log CFU/g indicating that it’s a major constituent of baker's yeast. Randomly, one hundred and forty bacterial strains were isolated from baker's yeast samples and were identified to its corresponding bacterial groups, using biochemical and morphological tests. It showed that it belonged to lactic acid bacteria, Bacilli and Micrococci. The molecular identification of the strains revealed that it is Bacillus subtilis, B. amyloliquefaciens, B. cereus, Geobacillus stearothermophilus, Lactobacillus plantarum, L. brevis, L. lactis, Micrococcus luteus and Kocuria rosea. The symbiotic interaction of the 140 isolates with S. cerevisiae was tested using disk diffusion method; revealed that six bacterial strains showed antimicrobial activity (inhibition zone ranged from 13.5 to 22.8 mm). The six strains belonged to genera Bacillus and Geobacillus. Further identification based on sequencing of 16S rDNA gene using universal primers revealed that the strains were identified as B. subtilis, B. amyloliquefaciens and G. stearothermophilus. The strains sequences were deposited in the GeneBank and have an accession numbers.