Specific Amino Acid Substitutions in the Proline-Rich Motif of the Rhizobium meliloti ExoP Protein Result in Enhanced Production of Low-Molecular-Weight Succinoglycan at the Expense of High-Molecular-Weight Succinoglycan

Abstract

ABSTRACT The production of the acidic exopolysaccharide succinoglycan (EPS I) by Rhizobium meliloti exoP * mutants expressing an ExoP protein lacking its C-terminal cytoplasmic domain and by mutants characterized by specific amino acid substitutions in the proline-rich motif (RX 4 PX 2 PX 4 SPKX 9 IXGXMXGXG) located from positions 443 to 476 of the ExoP protein was analyzed. The absence of the C-terminal cytoplasmic ExoP domain (positions 484 to 786) and the substitution of both arginine 443 by isoleucine 443 and proline 457 by serine 457 within the proline-rich motif resulted in enhanced production of low-molecular-weight (LMW) EPS I at the expense of high-molecular-weight (HMW) EPS I. The ratios of HMW to LMW EPS I of the wild type and mutant strains increased with osmolarity.