GENES-CODING FOR RESPIRATORY COMPLEXES MAP ON ALL 3 CHROMOSOMES OF THE PARACOCCUS-DENITRIFICANS GENOME

The genome of Paracoccus denitrificans (strain Pd1222) consists of thr ee 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 restricti on enzymes and sizes of resulting fragments are summed up, the three c hromosomes are composed of 1.83, 1.16, and 0.67 Mb. Since their migrat ion behavior relative to size standards is largely independent of elec trophoresis conditions, at least the two smaller chromosomes most like ly 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 cy tochrome c analysis. When the genome was analyzed with different probe s coding for respiratory enzymes, essential genes were found spread ov er all three chromosomes without any obvious clustering on any of the three forms.