Protein and lipopolysaccharide profiles of a salt-sensitive Rhizobium sp and its exopolysaccharide-deficient mutant

A fast-growing, salt-sensitive rhizobium (Rhizobium sp. ST1) with a narrow host range of infectivity was isolated from the root nodules of locally gro wn pigeonpea (Cajanus cajan). One of the Tn5 mutants of Rhizobium sp. ST1 w as exopolysaccharide (EPS) deficient (exo(-)) and showed a 50% growth inhib ition (GI (50)) at 350 mM NaCl, compared to the GI(50) value of the wild ty pe strain at 250 mM NaCl. Whole cell protein profiles of the wild type in t he presence of NaCl showed an overall increase in the levels of several pro teins (22, 38, 68, >97 kDa), whereas in its exo- mutant, certain low molecu lar weight outer membrane proteins (38 and 22 kDa) decreased. Other outer m embrane proteins (22, 38, 40, 42,62 and 68 kDa) also markedly decreased in both the wild type and the exo- mutant in the presence of salt. Similarly, both the wild type and the exo - mutant showed decreased levels of both the lipopolysaccharide (LPS) components (LPS I and LPS II) in the presence of NaCl. These observations suggest the possible involvement of the outer memb rane components, along with other factors, during growth under salt stress, in both salt-sensitive and relatively salt-tolerant strains of rhizobia. ( C) 2001 Elsevier Science Ltd. All rights reserved.