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

In the dairy industry, microbial exopolysaccharides (EPSs) produced by lact ic 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 suggest ed that EPSs produced by LAB may confer health benefits. Over the past few years, several studies have been initiated to further understand the geneti cs and biochemistry of microbial EPS biosynthesis. Eps clusters from differ ent strains of LAB have been identified. In this study, we present the homo logies shared by the genes present in the eps clusters from Streptococcus t hermophilus, Streptococcus macedonicus, Lactobacillus helveticus, Lactobaci llus delbrueckii subsp, bulgaricus and Lactococcus lactis strains. These ho mologies are striking and imply a common mechanism of EPS biosynthesis. Mos t interestingly, these clusters contain genes encoding putative glycosyltra nsferases (GTFs) that can be regarded as a toolbox of enzymes with a large variety of specificities for applications in polysaccharide engineering. (C ) 2001 Elsevier Science Ltd. All rights reserved.