The complete sequence of the 1,683-kb pSymB megaplasmid from the N2-fixing endosymbiont Sinorhizobium meliloti
- Turlough M. Finan*,†,‡,
- Stefan Weidner*,§,
- Kim Wong†,
- Jens Buhrmester§,
- Patrick Chain†,
- Frank J. Vorhölter§,
- Ismael Hernandez-Lucas†,
- Anke Becker§,
- Alison Cowie†,
- Jérôme Gouzy¶,
- Brian Golding†, and
- Alfred Pühler§
- †Department of Biology, McMaster University, 1280 Main Street West, Hamilton, ON, Canada L8S 4K1; §Universität Bielefeld, Fakultät für Biologie, Lehrstuhl für Genetik, Universitätsstrasse 25, D-33615 Bielefeld, Germany; and ¶Laboratoire de Biologie Moléculaire des Relations Plantes-Microorganismes, Unité Mixte de Recherche 215, Chemin de Borde Rouge, BP27, F-31326 Castanet Tolosan, France
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Communicated by Sharon R. Long, Stanford University, Stanford, CA (received for review March 13, 2001)
Abstract
Analysis of the 1,683,333-nt sequence of the pSymB megaplasmid from the symbiotic N2-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.
Footnotes
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↵ * T.M.F. and S.W. contributed equally to this work.
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↵ ‡ To whom reprint requests should be addressed. E-mail: finan{at}mcmaster.ca.
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Data deposition: The sequence reported in this paper has been deposited in the EMBL database (accession no. AL591985).
- Abbreviations:
- ABC,
- ATP-binding cassette;
- EPS,
- exopolysaccharide;
- CPS,
- capsular polysaccharide
- Copyright © 2001, The National Academy of Sciences
