Alkane Hydroxylase from Acinetobacter sp. Strain ADP1 Is Encoded by alkM and Belongs to a New Family of Bacterial Integral-Membrane Hydrocarbon Hydroxylases

Degradation of long-chain alkanes byAcinetobacter sp. strain ADP1 involves rubredoxin and rubredoxin reductase. We complemented a mutant deficient in alkane utilization and sequenced four open reading frames (ORFs) on the complementing DNA. Each of these ORFs was disrupted by insertional mutagenesis on the chromosome. As determined from sequence comparisons, ORF1 and ORF4 seem to encode a rotamase of the PpiC type and an acyl coenzyme A dehydrogenase, respectively. Disruption of these ORFs does not affect alkane utilization. In contrast, the two other ORFs,alkR andalkM , are essential for growth on alkanes as sole carbon sources.alkR encodes a polypeptide with extensive homology to AraC-XylS-like transcriptional regulators. It is located next toalkM , which encodes the terminal alkane hydroxylase, but is in the opposite orientation. Sequence homologies with other bacterial integral-membrane hydrocarbon hydroxylases suggest that AlkM may be the first member of a new protein family. The genes identified here are not linked to the rubredoxin- and rubredoxin reductase-encoding genes on theAcinetobacter sp. strain ADP1 chromosome.