The Genome Sequence of the Tomato-Pathogenic Actinomycete Clavibacter michiganensis subsp. michiganensis NCPPB382 Reveals a Large Island Involved in Pathogenicity

Lehrstuhl für Gentechnologie/Mikrobiologie, Center for Biotechnology (Cebitec), Lehrstuhl für Genetik, Universität Bielefeld, D-33594 Bielefeld, Germany

^* To whom correspondence should be addressed. Email: eichenlaub{at}uni-bielefeld.de.

	Abstract

Clavibacter michiganensis subsp. michiganensis (Cmm) is a plant-pathogenic actinomycete causing bacterial wilt and canker of tomato. The nucleotide sequence of the genome of strain NCPPB382 was determined. The chromosome is circular, consists of 3.298 Mb and has a high G+C content of 72.6%. Annotation revealed 3080 putative protein-encoding sequences; only 26 pseudogenes were detected additionally. Two rrn operons, 45 tRNAs and 3 small stable RNA genes were found. The two circular plasmids, pCM1 (27.4 kbp) and pCM2 (70.0 kbp), which carry pathogenicity genes and thus are essential for virulence, have lower G+C contents of 66.5% and 67.6%, respectively. In contrast to the closely related Clavibacter michiganensis subsp. sepedonicus, the genome of Cmm lacks complete insertion elements and transposons. The 129 kb chp-/tomA region of low G+C content near the chromosomal origin of replication was shown to be necessary for pathogenicity. This region carries numerous genes encoding proteins involved in uptake and metabolism of sugars and several serine proteases. There is evidence that single genes located in this region, especially the serine proteases, are required for an efficient colonization of the host. Although Cmm is mainly growing in the xylem of tomato plants, no evidence for pronounced genome reduction was found. Cmm seems to have as many transporters and regulators as typical soil-inhabiting bacteria. However, the apparent lack of a sulfate reduction pathway which renders Cmm dependent on reduced sulfur compounds for growth is probably the reason for the poor survival of Cmm in soil.