Finally, our AlkBa and the other AlkB of the same cluster (Fig.?1a) also group with sequences annotated as AlkB7 (Fig.?1b, PP?=?0��81), recently identified in strains closely related to R.?ruber (such as strains DEE5311 or DEE5151). This suggests the affiliation of AlkBa and all other enzymes non or misannotated CH5424802 in vivo
of the cluster to this new AlkB type. Although no substrate characterization was carried out for these enzymes, they were again found in bacteria that do not grow on volatile n-alkanes (Kim et?al. 2007). This supports our hypothesis about the putative function of AlkB7 from our two R.?ruber strains. Besides, our results obtained with resting cells suggest that hexane degradation in R.?ruber SP2B is not a constitutive phenomenon and is proceeded by an enzymatic system inducible only by a small range of linear alkanes (Verteporfin Rhodococcus sp. P14. However, no more information is currently available about this enzyme or about the alkane degradation VX770
range of this strain. As illustrated in the phylogenetic tree (Fig.?1a), this second partial AlkBb from both R.?ruber seems to belong to a new AlkB type (PP?=?1). Although other partial alkB amplified from rhodococcal strains have been classified into three new subtypes alkB5, -B6 or -B7 (Kim et?al. 2007), their sequence do not overlap with the known sequence of our alkBb gene. However, the AlkB3 sequence from Rhodococcus sp. P14, which groups with our AlkBb, is long enough to be used as a landmark, because its sequence overlaps with all those partial sequences. Accordingly, a new phylogenetic analysis was performed without AlkBb sequences but containing the new AlkB5, -B6 and -B7 sequences (Fig.?1b). The topology of this second tree is similar to the first one (Fig.?1a,b). The marker AlkB3 from Rhodococcus sp. P14 groups robustly with the rhodococcal AlkB5 (PP?=?1), suggesting that our partial AlkBb is an AlkB5. Therefore, both R.?ruber contain a similar second putative integral membrane alkane hydroxylase, which is probably neither responsible of the hexane degradation, because AlkB5 enzymes were only detected, so far, in Rhodococcus strains unable to use short-chain alkanes. Other bacterial systems, such as some P450 cytochromes belonging to different CYP families, are able to catalyse terminal alkane hydroxylation.