The pssB gene product of Rhizobium leguminosarum bv. trifolii is homologous to a family of inositol monophosphatases

Abstract

The Rhizobium leguminosarum bv. trifolii region encoding pssA and pssB genes was cloned. The pssB gene located upstream of the pssA encoded a 28.36-kDa protein which displayed 97.5% identity with the PssB of R. leguminosarum bv. viciae. Inactivation of the pssB gene by insertion of the lacZ-Gm r cassette resulted in the significant increased production of exopolysaccharide in comparison to the wild-type level. A mutant strain was also defective in nitrogen fixation suggesting a regulatory role of pssB in symbiosis with clover. z

Exopolysaccharide Biosynthesis in Rhizobium leguminosarum: From Genes to Functions

“…The gene was shown to be transcribed as a monocistronic mRNA [45]. Upstream of the pssA is the pssB gene encoding inositol monophosphatase [49][50][51]. Effects of mutations within the pssB gene on the synthesis of EPS and symbiotic behavior have been analyzed in the Rlv VF39 and Rlt TA1 backgrounds and have been shown to be contradictory.…”

“…Members of this family catalyze the formation of a phosphodiester bond between polyprenol phosphate and hexoso-1-phosphate, which is donated by nucleotide sugars. The pssA gene is highly conserved in R. leguminosarum biovars and R. etli [44][45][46]50]. The pssA mutants do not produce EPS and as a consequence impaired the normal development of the nitrogen-fixing nodules on the appropriate plant hosts and the formation of biofilms both in vitro and on root hairs [5,45,46,50].…”

“…The pssA gene is highly conserved in R. leguminosarum biovars and R. etli [44][45][46]50]. The pssA mutants do not produce EPS and as a consequence impaired the normal development of the nitrogen-fixing nodules on the appropriate plant hosts and the formation of biofilms both in vitro and on root hairs [5,45,46,50]. Some contradictory results exist concerning the influence of pssA mutations on the synthesis of CPS which displays similar structure to EPS in terms of glycosyl composition [5,30,62].…”

The Rhizobium leguminosarum bv. trifolii pssB gene product is an inositol monophosphatase that influences exopolysaccharide synthesis

“…The assembly of the repeating units of R. leguminosarum requires pssA, pssDE, pssC, and other not yet identified genes encoding glycosyl transferases (Borthakur et al 1988;Ivashina et al 1994;Król et al 1998;Pollock et al 1998;van Workum et al 1997). The pssB gene, located upstream of pssA, encodes a protein homologous to members of a family of inositol monophosphatases (IMPases) with well-conserved metaland phosphate-binding sites present in diverse prokaryotic and eukaryotic enzymes (Janczarek et al 1999). The nonpolar mutation in pssB results in increased EPS synthesis and a non-nitrogen-fixing phenotype of R. leguminosarum bv.…”

“…The nonpolar mutation in pssB results in increased EPS synthesis and a non-nitrogen-fixing phenotype of R. leguminosarum bv. trifolii mutant (Janczarek et al 1999).…”