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Microbiology. 2005 Jun;151(Pt 6):1839-1851. doi: 10.1099/mic.0.27852-0.

Comparative analysis of the exopolysaccharide biosynthesis gene clusters from four strains of Lactobacillus rhamnosus.

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Hopital Notre-Dame, 560 Sherbrooke Est, Montréal, QC, Canada H2L 4M1.
STELA Dairy Research Centre, Room 1316, Pavillon Paul-Comtois, Université Laval, Quebec, QC, Canada G1K 7P4.
Nutraceuticals and Functional Foods Institute (INAF), Université Laval, Quebec, QC, Canada G1K 7P4.
Laboratoire de Microbiologie et de Génétique Moléculaire, UMR CNRS/UCBL/INSA 5122, Université Lyon 1, 69622, Villeurbanne, France.
Food Research and Development Centre, Agriculture and Agri-Food Canada, St Hyacinthe, Quebec, Canada J2S 8E3.


The exopolysaccharide (EPS) biosynthesis gene clusters of four Lactobacillus rhamnosus strains consist of chromosomal DNA regions of 18.5 kb encoding 17 ORFs that are highly similar among the strains. However, under identical conditions, EPS production varies considerably among these strains, from 61 to 1611 mg l(-1). Fifteen genes are co-transcribed starting from the first promoter upstream of wzd. Nevertheless, five transcription start sites were identified by 5'-RACE PCR analysis, and these were associated with promoter sequences upstream of wzd, rmlA, welE, wzr and wzb. Six potential glycosyltransferase genes were identified that account for the assembly of the heptasaccharide repeat unit containing an unusually high proportion of rhamnose. Four genes involved in the biosynthesis of the sugar nucleotide precursor dTDP-L-rhamnose were identified in the EPS biosynthesis locus, which is unusual for lactic acid bacteria. These four genes are expressed from their own promoter (P2), as well as co-transcribed with the upstream EPS genes, resulting in coordinated production of the rhamnose precursor with the enzymes involved in EPS biosynthesis. This is believed to be the first report demonstrating that the sequence, original organization and transcription of genes encoding EPS production are highly similar among four strains of Lb. rhamnosus, and do not vary with the amount of EPS produced.

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