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

被引:80
作者
Kereszt, A
Kiss, E
Reuhs, BL
Carlson, RW
Kondorosi, S
Putnoky, P
机构
[1] Hungarian Acad Sci, Inst Genet, Biol Res Ctr, H-6701 Szeged, Hungary
[2] Univ Georgia, Complex Carbohydrate Res Ctr, Athens, GA 30602 USA
[3] CNRS, Inst Sci Vegetales, F-91198 Gif Sur Yvette, France
关键词
D O I
10.1128/JB.180.20.5426-5431.1998
中图分类号
Q93 [微生物学];
学科分类号
071005 ; 100705 ;
摘要
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 phi 16-3. 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 phi 16-3-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-1 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.
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页码:5426 / 5431
页数:6
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