Characterization of the transcriptional regulation of the tarIJKL locus involved in ribitol-containing wall teichoic acid biosynthesis in Lactobacillus plantarum.

Lactobacillus plantarum strains produce either glycerol (Gro)- or ribitol (Rbo)-backbone wall teichoic acid (WTA) (Gro-WTA and Rbo-WTA, respectively). The strain WCFS1 has been shown to be able to activate the tarIJKL locus involved in Rbo-WTA synthesis when the tagD1F1F2 locus for Gro-WTA synthesis was mutated, resulting in switching of the native Gro-WTA into Rbo-WTA. Here, we identify a regulator involved in the WTA backbone alditol switching and activation of the tarIJKL locus. Promoter reporter assays of the tarI promoter (Ptar) demonstrated its activity in the Rbo-WTA-producing mutant derivative (ΔtagF1-2) but not in the parental strain WCFS1. An electrophoresis mobility shift assay using a Ptar nucleotide fragment showed that this fragment bound to Ptar-binding protein(s) in a cell-free extract of WCFS1. Three proteins were subsequently isolated using Ptar bound to magnetic beads. These proteins were isolated efficiently from the lysate of WCFS1 but not from the lysate of its ΔtagF1-2 derivative, and were identified as redox-sensitive transcription regulator (Lp_0725), catabolite control protein A (Lp_2256) and TetR family transcriptional regulator (Lp_1153). The role of these proteins in Ptar regulation was investigated by knockout mutagenesis, showing that the Δlp_1153 mutant expressed the tarI gene at a significantly higher level, supporting its role as a repressor of the tarIJKL locus. Notably, the Δlp_1153 mutation also led to reduced expression of the tagF1 gene. These results show that Lp_1153 is a regulatory factor that plays a role in WTA alditol switching in Lb. plantarum WCFS1 and we propose to rename this gene/protein wasR/WasR, for WTA alditol switch regulator.

Functional analysis of glycosyltransferase genes from Lactococcus lactis and other gram-positive cocci: complementation, expression, and diversity.

Sixteen exopolysaccharide (EPS)-producing Lactococcus lactis strains were analyzed for the chemical compositions of their EPSs and the locations, sequences, and organization of the eps genes involved in EPS biosynthesis. This allowed the grouping of these strains into three major groups, representatives of which were studied in detail. Previously, we have characterized the eps gene cluster of strain NIZO B40 (group I) and determined the function of three of its glycosyltransferase (GTF) genes. Fragments of the eps gene clusters of strains NIZO B35 (group II) and NIZO B891 (group III) were cloned, and these encoded the NIZO B35 priming galactosyltransferase, the NIZO B891 priming glucosyltransferase, and the NIZO B891 galactosyltransferase involved in the second step of repeating-unit synthesis. The NIZO B40 priming glucosyltransferase gene epsD was replaced with an erythromycin resistance gene, and this resulted in loss of EPS production. This epsD deletion was complemented with priming GTF genes from gram-positive organisms with known function and substrate specificity. Although no EPS production was found with priming galactosyltransferase genes from L. lactis or Streptococcus thermophilus, complementation with priming glucosyltransferase genes involved in L. lactis EPS and Streptococcus pneumoniae capsule biosynthesis could completely restore or even increase EPS production in L. lactis.

Exopolysaccharide biosynthesis in Lactococcus lactis NIZO B40: functional analysis of the glycosyltransferase genes involved in synthesis of the polysaccharide backbone.

We used homologous and heterologous expression of the glycosyltransferase genes of the Lactococcus lactis NIZO B40 eps gene cluster to determine the activity and substrate specificities of the encoded enzymes and established the order of assembly of the trisaccharide backbone of the exopolysaccharide repeating unit. EpsD links glucose-1-phosphate from UDP-glucose to a lipid carrier, EpsE and EpsF link glucose from UDP-glucose to lipid-linked glucose, and EpsG links galactose from UDP-galactose to lipid-linked cellobiose. Furthermore, EpsJ appeared to be involved in EPS biosynthesis as a galactosyl phosphotransferase or an enzyme which releases the backbone oligosaccharide from the lipid carrier.

Molecular characterization of the plasmid-encoded eps gene cluster essential for exopolysaccharide biosynthesis in Lactococcus lactis.

Lactococcus lactis strain NIZO B40 produces an extracellular phosphopolysaccharide containing galactose, glucose, and rhamnose. A 40 kb plasmid encoding exopolysaccharide production was isolated through conjugal transfer of total plasmid DNA from strain NIZO B40 to the plasmid-free L. lactis model strain MG1614 and subsequent plasmid curing. A 12 kb region containing 14 genes with the order epsRXABCDEFGHIJKL was identified downstream of an iso-IS982 element. The predicted gene products of epsABCDEFGHIJK show sequence homologies with gene products involved in exopolysaccharide, capsular polysaccharide, lipopolysaccharide, or teichoic acid biosynthesis of other bacteria. Transcriptional analysis of the eps gene cluster revealed that the gene cluster is transcribed as a single 12 kb mRNA. The transcription start site of the promoter was mapped upstream of the first gene epsR. The involvement of epsD in exopolysaccharide (EPS) biosynthesis was demonstrated through a single gene disruption rendering an exopolysaccharide-deficient phenotype. Heterologous expression of epsD in Escherichia coli showed that its gene product is a glucosyltransferase linking the first sugar of the repeating unit to the lipid carrier.