The complete sequence of the 1,683-kb pSymB megaplasmid from the N 2 -fixing endosymbiont Sinorhizobium meliloti

• DOI: 10.1073/pnas.161294698
• Publication Date: 2002-07-26T14:34:10Z
• Authors: Turlough M. Finan; Stefan Weidner; Kim Wong; Jens Buhrmester; Patrick Chain; Frank J. Vorhölter; Ismael Hernandez-...; Anke Becker; Alison Cowie; Jérôme Gouzy; Brian Golding; Alfred Pühler
• Keywords: DNA, Bacterial; Lipopolysaccharides; 0301 basic medicine; Chaperonins; Molecular Sequence Data; Drug Resistance, Microbial; RNA, Transfer, Arg; Replication Origin; Gene Expression Regulation, Bacterial; Sequence Analysis, DNA; Enzymes; 03 medical and health sciences; Bacterial Proteins; Species Specificity; Genes, Bacterial; Nitrogen Fixation; Carbohydrate Metabolism; Replicon; Carrier Proteins; Gene Library; Plasmids; Sinorhizobium meliloti

Analysis of the 1,683,333-nt sequence of the pSymB megaplasmid from the symbiotic N 2 -fixing bacterium Sinorhizobium meliloti revealed that the replicon has a high gene density with a total of 1,570 protein-coding regions, with few insertion elements and regions duplicated elsewhere in the genome. The only copies of an essential arg-tRNA gene and the minCDE genes are located on pSymB. Almost 20% of the pSymB sequence carries genes encoding solute uptake systems, most of which were of the ATP-binding cassette family. Many previously unsuspected genes involved in polysaccharide biosynthesis were identified and these, together with the two known distinct exopolysaccharide synthesis gene clusters, show that 14% of the pSymB sequence is dedicated to polysaccharide synthesis. Other recognizable gene clusters include many involved in catabolic activities such as protocatechuate utilization and phosphonate degradation. The functions of these genes are consistent with the notion that pSymB plays a major role in the saprophytic competence of the bacteria in the soil environment.