Molecular organization and functionality of exopolysaccharide gene clusters in lactic acid bacteria

In the dairy industry, microbial exopolysaccharides (EPSs) produced by lactic acid bacteria (LAB) in situ are used to improve the texture of fermented dairy products such as yoghurt or cheese. In addition, it has been suggested that EPSs produced by LAB may confer health benefits. Over the past few years, several studies have been initiated to further understand the genetics and biochemistry of microbial EPS biosynthesis. Eps clusters from different strains of LAB have been identified. In this study, we present the homologies shared by the genes present in the eps clusters from Streptococcus thermophilus, Streptococcus macedonicus, Lactobacillus helveticus, Lactobacillus delbrueckii subsp. bulgaricus and Lactococcus lactis strains. These homologies are striking and imply a common mechanism of EPS biosynthesis. Most interestingly, these clusters contain genes encoding putative glycosyltransferases (GTFs) that can be regarded as a toolbox of enzymes with a large variety of specificities for applications in polysaccharide engineering.