Multiple Extradiol Dioxygenase Genes Are Distributed on the Genomes of the Biphenyl Degrading Strains Rhodococcus erythropolis TA421 and Rhodococcus globerulus P6

Growth of R. erythropolis TA421 on biphenyl and cometabolic turnover of PCB is associated with the linear 500-kb plasmid pTA421 (Kosono et al. 1997). Similar to Rhodococcus sp. strain RHA1 (Sect. 3.2.1), strain TA421 contains a multiplicity of bphC genes coding for 2,3-dihydroxybiphenyl 1,2-dioxygenases. Three of the seven bphC genes are located on its linear plasmid pTA421 (Table 1; Kosono et al. 1997; Arai et al. 1998). The plasmid-borne bphC3 is part of the bph locus depicted in Fig. 5; its deduced gene product shows 70% identity to BphC1 of pRHL1 and IpbC encoded by the linear plasmid pBD2 (see Sect. 3.2.4). The bphC4 gene was identified in a bphA1A2A3BA4C4D cluster which is also located on the plasmid, suggesting that the extradiol dioxygenases BphC3 and/or BphC4 indeed are involved in biphenyl degradation (Arai et al. 1998). The BphC2 and BphC3 proteins of strain TA421 share 95.3 and 99.7% identity to BphC2 and BphC1, respectively, of R. globerulus P6 (Arai et al. 1998), suggesting a recent common ancestor of the corresponding genes. Strain P6 harbors two probably linear plasmids pLP6 and pSP6 (Table 1); however, whilst pSP6 contains the bphC3 and bphC4 homologues, a bphC2 gene is located on both plasmids (Kosono et al. 1997). Eight bphC genes were identified in R. rhodochrous K37. Two of those (bphC6, bphC8) are located on a 200-kb plasmid (Table 1), whereas the remaining six appear to be located on the chromosome (Taguchi et al. 2004).

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