Efficient Screening Methods for Glucosyltransferase Genes in Lactobacillus Strains

Limited information is available about homopolysac-charide synthesis in the genus Lactobacillus. Using efficient screening techniques, extracellular glucosyl-transferase (GTF) enzyme activity, resulting in a-glucan synthesis from sucrose, was detected in various lactoba-cilli. PCR with degenerate primers based on homologous boxes of known glucosyltransferase (gtf) genes of lactic acid bacteria strains allowed cloning of fragments of 10 putative gtf genes from eight different glucan producing Lactobacillus strains (five Lactobacillus reuteri strains, one Lactobacillus fermentum strain, one Lactobacillus sake strain and one Lactobacillus parabuchneri strain). Sequence analysis revealed that these lactobacilli pos-sess a large variation of (putative) gtf genes, similar to what has been observed for Leuconostoc and Strepto-coccus strains. Homologs of GTFA of Lb. reuteri 121 (synthesizing reuteran, a unique glucan with a-(10/4) and a-(10/6) glycosidic bonds) (Kralj et al., 2002) were found in three of the four other Lb. reuteri strains tested. The other Lactobacillus GTF fragments showed the highest similarity with GTF enzymes of Leuconostoc spp