Microbes and Beneficial Microbes

Biography

Biography: Seipati P. Tenyane

Abstract

Saccharomyces cerevisiae strains are reported to either promote or, most frequently, inhibit lactic acid bacteria strains (LAB). Unfortunately, it is unknown what drives either positive or negative interactions between these strains. To investigate underlying interaction mechanisms between wine-related yeast and bacteria and their impact on malolactic fermentation (MLF), a directed evolution (DE) approach was designed to directly evolve a Lactobacillus plantarum strain using two strains of S. cerevisiae, EC1118 and Cross Evolution, as selective drivers. In this strategy, the bacterial population evolved continuously in co-culture with the inhibitory strains of yeast over successive generations. The yeast population, however, was re-inoculated from the same mother culture for each sequential batch fermentation. In this design, the yeast ‘driver’ strains cannot evolve, and improved growth of the evolving bacterial species is a direct function of their ability to compete with the specific yeast strain.  Analysis of evolved isolates from the bacterial populations after only 50 generations revealed surprisingly vast differences in the phenotypes of isolates. The data show increased growth of evolved isolates compared to the parent strain as well as showing yeast-specific phenotypes with regard to the rate of malic acid consumption. Whole-genome sequencing of selected strains was carried out to elucidate the genetic changes which underpin the evolved phenotypes observed. Gene ontology revealed amino acid metabolism as a DE target, with specific gene targets including amino acid biosynthetic process (argD, argJ, carB, hisB, hisE, hutI), glutamine metabolic process (glmS) and amino acid transmembrane transport (glnQ, rocC).  To our knowledge, this is the first study to use a biotic selective pressure (S. cerevisiae) to evolve Lb. plantarum for the improvement of MLF and to investigate yeast-bacteria interactions.