Biosynthesis of the exopolysaccharide galactoglucan in Sinorhizobium meliloti is subject to a complex control by the phasphate-dependent regulator PhoB and the proteins ExpG and MucR

被引:65
作者
Rüberg, S [1 ]
Pühler, A [1 ]
Becker, A [1 ]
机构
[1] Univ Bielefeld, Fak Biol, Lehrstuhl Genet, D-33501 Bielefeld, Germany
来源
MICROBIOLOGY-UK | 1999年 / 145卷
关键词
phosphate regulation; PHO box; Rhizobium meliloti;
D O I
10.1099/13500872-145-3-603
中图分类号
Q93 [微生物学];
学科分类号
071005 ; 100705 ;
摘要
The soil bacterium Sinorhizobium meliloti (Rhizobium meliloti) has the ability to produce the alternative exopolysaccharide galactoglucan (EPS II) in addition to succinoglycan (EPS I). In the wild-type strain EPS II production is induced by phosphate-limiting conditions or by extra copies of the exp gene cluster. Based on similarities to transcriptional regulators of the MarR family, an additional putative regulatory gene, expG, was identified in the exp gene cluster. Using exp-laci! transcriptional fusions, a stimulating effect of extra copies of this expG gene on the transcription of all exp complementation groups was determined. Phosphate limitation also resulted in increased expression of the exp-lacZ fusions. This increase was reduced in strains characterized by a deletion of expG. The previously reported high level of exp gene transcription in a mucR mutant was further elevated under phosphate-limiting conditions. The expA, expD, expG and expE promoters contain sequences with similarities to the PHO box known as the PhoB-binding site in phosphate-regulated promoters in Escherichia coli. The S. meliloti phoB gene was required for the activation of exp gene expression under phosphate limitation, but not for induction of exp expression by MucR or ExpG.
引用
收藏
页码:603 / 611
页数:9
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