Identification of a glucan synthase gene potentially coding for exopolysaccharide production by Propionibacterium freudenreichii subsp. sherman

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English. A gene potentially coding for exopolysaccharide (EPS) biosynthesis was identified in the genome sequence of Propionibacterium freudenreichii subsp. shermanii strain CIP 103027. The predicted protein product of this gene, designated Pps, best aligned with Tts, a polysaccharide synthase gene of Streptococcus pneumoniae type 37, which is responsible for the production of a glucan capsular polysaccharide. Pps also showed similarity with the putative glucan synthase Dps of Pediococcus damnosus and Oenococcus oeni. Specific primers were designed in order to detect the presence of pps in other P. freudenreichii subsp. shermanii strains by PCR amplification using total genomic DNA. The gene was detected in all the 12 strains tested. The same primers failed to detect the gene in an EPS-producing strain of Propionibacterium acidipropionicii, suggesting that the gene is not present or is sufficiently divergent in sequence to prevent amplification. Pps gene was totally sequenced for 8 strains, and seems to be very conserved, as less than 1 % of nucleotides differed from one strain to another. In order to evaluate pps gene expression, total RNA of 3 strains was extracted at different growth phases in YEL broth. The presence of mRNA corresponding to the gene was detected by RT-PCR in all 3 strains during exponential and stationary growth phases. This work is the first identification of a polysaccharide synthase gene of P. freudenreichii, and further studies need to be undertaken to measure the variability among strains in the production of capsular EPS.