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

Article Abstract:

Exopolysaccharide galactoglucan (EPS II) production in the wild-type strain of the soil bacterium Sinorhizobium meliloti is induced by phosphate-limiting conditions or by extra copies of the exp gene cluster. Based on similarities to the transcriptional regulators of the MarR family, an additional putative regulatory gene, expG, was determined in the exp gene cluster. Employing exp-lacZ transcriptional fusions, a stimulating effect of extra copies of this expG on the transcription of all exp complementation groups was determined.

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The symbiotic phenotypes of exopolysaccharide-defective mutants of Rhizobium sp. strain TAL1145 do not differ on determinate- and indeterminate-nodulating tree legumes

Article Abstract:

Three classes of exoploysaccharide (EPS) defective mutants of TAL1145 and tested them on indeterminate and determinate-nodulating hosts for nodulation and nitrogen fixation. Results reveal that the exo mutants of TAL1145 have similar nodulation pheneotypes on both determinate and indeterminate-nodulating hosts. Results also show that the three classes of EPS-defective mutants were located within 10.8 kb region and complemented by two overlapping cosmids.

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The Sinorhizobium meliloti ExpE1 protein secreted by a type I secretion system involving EXpD1 and ExpD2 is required for biosynthesis or secretion of the exopolysaccharide galactoglucan

Article Abstract:

The expD1, expD2, and expE1 genes of Sinorhizobium meliloti are required for the synthesis or secretion of galactoglucan. Nitrogen-fixing bacteria that cannot produce exopolysaccharides can form nodules on the host plant but cannot invade the nodule.

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