Exopolysaccharide-producing strains of thermophilic lactic acid bacteria cluster into groups according to their EPS structure

Aims: To compare galactose-negative strains of Streptococcus thermophilus a nd Lactobacillus delbrueckii subspecies bulgaricus isolated from fermented milk products and known to produce exopolysaccharides (EPSs). Methods and Results: The structures of the EPSs were determined using nucle ar magnetic resonance (NMR) and their genetic relationships determined usin g restriction endonuclease analysis (REA) and random amplification of polym orphic DNA (RAPD). Similar groupings were apparent by REA and RAPD, and eac h group produced an EPS with a particular subunit structure. Conclusions: Although none of the strains assimilated galactose, all insert ed a high proportion of galactose into their EPS when grown in skimmed milk , and fell into three distinct groups. Significance and Impact of the Study: This information should help in an un derstanding of genetic exchanges in lactic acid bacteria.