Genes coding for respiratory complexes map on all three chromosomes of the Paracoccus denitrificans genome
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© Springer-Verlag 1998
O R I G I N A L PA P E R
Christine Winterstein · Bernd Ludwig
Genes coding for respiratory complexes map on all three chromosomes of the Paracoccus denitrificans genome
Received: 10 August 1997 / Accepted: 10 November 1997
Abstract The genome of Paracoccus denitrificans (strain Pd1222) consists of three distinct DNA molecules when separated by standard pulsed-field gel electrophoresis with apparent molecular sizes of approximately 2, 1.1, and 0.64 Mb. When the separated chromosomes are digested by restriction enzymes and sizes of resulting fragments are summed up, the three chromosomes are composed of 1.83, 1.16, and 0.67 Mb. Since their migration behavior relative to size standards is largely independent of electrophoresis conditions, at least the two smaller chromosomes most likely represent linear molecules. The size analysis presented here allows an unequivocal distinction between groups of different strains of P. denitrificans and of Thiosphaera pantotropha, confirming an earlier cytochrome c analysis. When the genome was analyzed with different probes coding for respiratory enzymes, essential genes were found spread over all three chromosomes without any obvious clustering on any of the three forms. Key words Pulsed-field gel electrophoresis · Megaplasmid · Thiosphaera pantotropha · Paracoccus denitrificans · Genome size Abbreviation PFG(E) Pulsed-field gel (electrophoresis)
Introduction Paracoccus denitrificans, a gram-negative soil bacterium, has gained widespread attention recently as a model organism for the study of processes of electron transport and energy transduction. Being a member of the α3 subclass of Proteobacteria (Woese 1987), its evolutionary relationship to present-day mitochondria has been noted and con-
C. Winterstein · B. Ludwig (Y) Molecular Genetics, Institute of Biochemistry, Biozentrum, Marie-Curie-Strasse 9, D-60439 Frankfurt, Germany Tel.+49-69-798-29237; Fax +49-69-798-29244 e-mail: [email protected]
firmed in many instances. Its adaptability to various carbon and energy sources and to other environmental conditions is reflected by the expression of a branched electron transport chain and the use of different terminal electron acceptors. As basic equipment, the typical mitochondrial redox complexes have been found; however, they exhibit a much simpler subunit structure in this bacterium (Yagi 1993; Berry and Trumpower 1985; Ludwig 1987). At the same time, the genetic accessibility of the organism has been worked out (Gerhus et al. 1990; Van Spanning et al. 1991 b): methods and plasmids for gene transfer into P. denitrificans have been developed, allowing (1) deletions by recombinational events and specific replacements of target genes by suitable resistance gene markers, and (2) expression of site-directed mutations in gene copies coded on broad-host-range plasmids maintained in trans. The 3D structure of one of the terminal oxidases of P. denitrificans, cytochrome c oxidase, has recently been solved (Iwata et al. 1995); in conjunction with the
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