Functional characterization of two alkane hydroxylases in a versatile Pseudomonas aeruginosa strain NY3

Pseudomonas aeruginosa strain NY3 has an extraordinary capacity to utilize a wide range of substrates, including n –alkanes of lengths C 5 to C 34 , aromatic compounds, phenols, diesel and crude oil, and it can produce a variety of small bioactive molecules, including rhamnolipids, which can enhance its metabolic capacity for hydrophobic organic pollutants. This capacity makes NY3 a good candidate for use in environmental pollution remediation. Alkane hydroxylases catalyze both the initial and rate-limiting step of the terminal oxidation of n –alkanes. To better understand the genetic mechanisms by which P. aeruginosa NY3 degrades such a wide range of n –alkanes, two putative coding genes of alkane hydroxylases were functionally characterized using a gene-knockout approach with three different degradation systems. The single n –alkane test indicated that the hydroxylase AlkB2 acted in the early growth phase and played a major role in the utilization of C 12 –C 18 . However, a double mutant showed a trend towards recovery when C 20 –C 24 were used as sole carbon source. This suggests that there are other enzymes capable of utilizing n –alkanes longer than C 20 . Tests of both artificial n –alkanes mixture and crude oil-containing waste water showed similar results, suggesting that both AlkB1 and AlkB2 are involved in n –alkane degradation, and, moreover, that AlkB2 plays a major role. Finally, given the wider functional range of both AlkBs in the mixture of n –alkanes compared to that of single n –alkanes, these results hint at co-metabolism.