Novel rkp gene clusters of Sinorhizobium meliloti involved in capsular polysaccharide production and invasion of the symbiotic nodule: the rkpK gene encodes a UDP-glucose dehydrogenase

The production of exopolysaccharide (EPS) was shown to be required for the infection process by rhizobia that induce the formation of indeterminate nodules on the roots of leguminous host plants. In Sinorhizobium meliloti (also known as Rhizobium meliloti) Rm41, a capsular polysaccharide (KPS) analo...

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Bibliographic Details
Published in:Journal of bacteriology 1998-10, Vol.180 (20), p.5426-5431
Main Authors: Kereszt, A, Kiss, E, Reuhs, B L, Carlson, R W, Kondorosi, A, Putnoky, P
Format: Article
Language:English
Subjects:
Bacterial Capsules - biosynthesis
Bacteriology
Carbohydrate Epimerases - genetics
Enzymes
Escherichia coli
Flowers & plants
Genes
Genes, Bacterial
Genetic Complementation Test
Genetics
Molecular Sequence Data
Multigene Family
Mutagenesis, Insertional
Open Reading Frames
Operon - genetics
Plant Microbiology
Plant Roots - microbiology
Polysaccharides, Bacterial - biosynthesis
Rhizobium meliloti
Sequence Homology, Amino Acid
Sinorhizobium meliloti
Sinorhizobium meliloti - enzymology
Sinorhizobium meliloti - genetics
Symbiosis - genetics
Uridine Diphosphate Glucose Dehydrogenase - genetics
Uridine Diphosphate Glucuronic Acid - metabolism
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Summary:The production of exopolysaccharide (EPS) was shown to be required for the infection process by rhizobia that induce the formation of indeterminate nodules on the roots of leguminous host plants. In Sinorhizobium meliloti (also known as Rhizobium meliloti) Rm41, a capsular polysaccharide (KPS) analogous to the group II K antigens of Escherichia coli can replace EPS during symbiotic nodule development and serve as an attachment site for the strain-specific bacteriophage phi16-3. The rkpA to -J genes in the chromosomal rkp-1 region code for proteins that are involved in the synthesis, modification, and transfer of an as-yet-unknown lipophilic molecule which might function as a specific lipid carrier during KPS biosynthesis. Here we report that with a phage phi16-3-resistant population obtained after random Tn5 mutagenesis, we have identified novel mutants impaired in KPS production by genetic complementation and biochemical studies. The mutations represent two novel loci, designated the rkp-2 and rkp-3 regions, which are required for the synthesis of rhizobial KPS. The rkp-2 region harbors two open reading frames (ORFs) organized in monocistronic transcription units. Although both genes are required for normal lipopolysaccharide production, only the second one, designated rkpK, is involved in the synthesis of KPS. We have demonstrated that RkpK possesses UDP-glucose dehydrogenase activity, while the protein product of ORF1 might function as a UDP-glucuronic acid epimerase.
ISSN:0021-9193
1098-5530
DOI:10.1128/JB.180.20.5426-5431.1998