Abstract

The microorganisms contained in fermented foods are known to harbor metabolic products, possibly improving human and animal health. However, despite several studies on the functional effects of fermented foods, isolation and identification of the effective Bacillus species strains are still in progress. The objective of this study was to molecularly identify biofilm-producing Bacillus spp. (BPB) and yeasts from fermented food sources and to study their interactions with the Lysinibacillus louembei strain. A total of 133 isolates of Bacillus as well as 32 isolates of yeast were obtained for detailed identification and investigation. Based on a combination of phenotypic and molecular characterization using fibE polymerase chain reaction (PCR) multiplex and ITS-PCR techniques, species of Bacillus were identified as Bacillus pumilus (12%), Bacillus subtilis (12%), Bacillus safensis (6%), Bacillus amyloliquefaciens (6%), Bacillus licheniformis (6%), and Saccharomyces cerevisiae (0.05%). The yfiQ, epsH, ymcA, and tasA genes involved in the biofilm formation process were amplified by using PCR multiplex in B. subtilis, B. licheniformis, and B. pumilus have been identified and confirmed. As a phenotypic result, 45% of isolates of BPB by using the Congo Red Agar method (CRA) have been identified. The ability of Bacillus and yeasts to produce biosurfactants was tested by using the emulsification index (EI24). 65 and 69% of Bacillus and yeast isolates were able to emulsify petrol. 56% of the crude extract of biosurfactants from Bacillus isolates demonstrated antimicrobial activity against Escherichia coli, Staphylococcus aureus, and Salmonella species cultures were done between Bacillus spp., S. cerevisiae, and L. louembei. As a result, commensalism-like interactions were obtained in yeast strain V3 and B. pumilus strain VB15 and L. louembei and B. amyloliquefaciens, competition-like interactions in S. cerevisiae strain P3 and Bacillus spp. strain VP11, and amensalism-like interactions with B. pumilus and S. cerevisiae and Bacillus spp. strain VP34 and S. cerevisiae strain P1. These results illustrate that microorganisms maintain different relationships that occur during fermentation process.

Keys words: Bacillus, Saccharomyces cerevisiae, Lysinibacillus louembei, fermented foods, microorganism interactions, biosurfactants, biofilms.