Size Distribution of Succinoglycan (EPS I) Produced by Different Sinorhizobium meliloti ExoP Mutants and Analysis of their Symbiotic Properties

The acidic exopolysaccharide succinoglycan (EPS I) produced by Sinorhizobium meliloti (formerly Rhizobium meliloti) consists of a high molecular weight (HMW) and a low molecular weight (LMW) fraction. The LMW EPS I fraction is believed to play an important role in the infection of Medicago sativa root nodules by the microsymbiont. In S. meliloti, the products of 19 exo and 2 exs genes are involved in the biosynthesis, the polymerization and the transport of EPS I (Becker et al. 1995a, Gonzalez et al. 1996). One of these gene products is the S. meliloti ExoP protein, which might be involved in determining the ratio of HMW to LMW EPS I. The N-terminal mainly periplasmic domain of ExoP is similar to proteins involved in the determination of O-antigen chain length, whereas the cytoplasmic C-terminal domain is characterized by a potential ATP binding motif (Becker et al. 1995b).