Sinorhizobium meliloti mutants lacking PTS enzymes HPr or EIIA are altered in diverse processes including carbon metabolism, cobalt requirements and succinoglycan production

University of Connecticut, Department of Molecular and Cell Biology, 91 N. Eagleville Rd., U-3125, Storrs, CT 06269-3125

^* To whom correspondence should be addressed. Email: daniel.gage{at}uconn.edu.

	Abstract

Sinorhizobium meliloti is a member of the -proteobacteria that fixes nitrogen when living in symbiosis. Genes for an incomplete phospho-transferase system (PTS) are found in the genome of S. meliloti. The genes present code for Hpr and ManX (an EIIA^man-type enzyme). HPr and EIIA regulate carbon utilization in other bacteria. hpr and manX in-frame deletion mutants exhibited altered carbon metabolism and other phenotypes as well. Loss of HPr resulted in partial relief from succinate-mediated catabolite repression (SMCR), extreme sensitivity to cobalt limitation, rapid die-off during stationary phase and altered succinoglycan production. Loss of manX lowered expression of melA-agp and lac, the operons needed for utilization of - and -galactosides, slowed growth in diverse carbon sources and enhanced accumulation of high-molecular-weight succinoglycan. A strain with deletions of both hpr and manX exhibited phenotypes similar to the strain with a single hpr deletion. Despite these strong phenotypes, deletion mutants showed wild type nodulation and nitrogen fixation when inoculated on Medicago sativa. The results show that HPr and ManX(EIIA^man) are involved in more than carbon regulation in S. meliloti, and suggest that the phenotypes observed occur through action of HPr or one of its phosphorylated forms.