Plant, Animal & Microbe Genomes X Conference

January 12-16, 2002
Town & Country Convention Center
San Diego, CA

Session: Microbe Session Lecture
            

DOES THE ALFALFA SYMBIONT SINORHIZOBIUM MELILOTI CONTAIN THREE CHROMOSOMES?

¹ DEPT. OF BIOLOGY, MCMASTER UNIVERSITY, 1280 MAIN ST. W., HAMILTON ONTARIO, CANADA, L8S 4K1

Sinorhizobium meliloti is a gram negative alpha-proteobacteria that forms nitrogen-fixing root-nodules on alfalfa. The S. meliloti strain SU47 genome contains a typical chromosome of 3.64 Mb and two megaplasmids of 1.35 Mb (pSymA) and 1.68 Mb (pSymB). Both pSymA and pSymB carry genes required for nodule formation and nitrogen fixation. The nucleotide sequence and annotation of these replicons were recently reported by an international consortium with members from France (Rennes and Toulouse), Germany (University of Bielefeld), the USA (Stanford University) and Canada (McMaster University). The McMaster group employed an oriT-directed in vivo recombination procedure to clone specific 60 to 270 kb regions of the S. meliloti genome. Results from annotation analysis of the genome sequence will be discussed with respect to the nature of the megaplasmid replicons and identification of genes of the PHO regulon. The latter represents genes whose expression is regulated by the PhoB protein in response to limiting concentrations of phosphate.