Alkane Oxidation Genes Located on pREL1 of Rhodococcus erythropolis PR4

Rhodococcus erythropolis PR4, an alkane degrading strain, contains the linear plasmid pREL1 and two circular plasmids pREC1 and pREC2 (Table 1), which have been sequenced completely (Sekine et al. 2006). The plasmids contain modular segments that are homologous to corresponding regions of other rhodococcal plasmids. While pREL1 shares several regions of homology with pBD2 of R. erythropolis strain BD2, putative alkane degradation genes, organized in two clusters and flanked by transposon and insertion sequences, are located outside these common regions. The first degradative cluster includes genes presumed to code for fatty acid-CoA ligase, alcohol dehydrogenase, aldehyde dehydrogenase, and a three-component n-alkane monooxygenase system. The second putative catabolic gene cluster comprises genes of another alkane monooxygenase and a truncated fatty acid-CoA ligase. Differences in the G+C contents of the two gene clusters and differences in the deduced amino acid sequences of the gene products suggested that independent gene transfer events have led to the recruitment of these two clusters. A complete set of genes for the P-oxidation of fatty acids, which has been discussed to represent a genomic island of extraneous origin, is located on the circular plasmid pREC1, suggesting that the combined action of the gene products of pREL1 and pREC1 contributes to alkane mineralization. On the other hand, the genome contains additional (and in some cases multiple) copies of genes encoding AlkB-like alkane monooxygenase, AlkG- and AlkT-like rubredoxin and rubredoxin reductase, respectively, putative alcohol dehydrogenase AlkJ, and aldehyde dehydrogenase AlkH, as well as AlkK-like fatty acid-CoA ligase, indicating that R. erythropolis PR4 may be able to degrade alkanes even without the proteins encoded on pREL1 (Sekine et al. 2006).

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