Characterization of the Medium- and Long-Chain <i>n</i>-Alkanes Degrading <i>Pseudomonas aeruginosa</i> Strain SJTD-1 and Its Alkane Hydroxylase Genes

<div><p>A gram-negative aliphatic hydrocarbon-degrading bacterium SJTD-1 isolated from oil-contaminated soil was identified as <i>Pseudomonas aeruginosa</i> by comparative analyses of the 16S rRNA sequence, phenotype, and physiological features. SJTD-1 could efficiently mineralize medium- and long-chain <i>n-</i>alkanes (C₁₂-C₃₀) as its sole carbon source within seven days, showing the most optimal growth on <i>n</i>-hexadecane, followed by <i>n</i>-octadecane, and <i>n</i>-eicosane. In 36 h, 500 mg/L of tetradecane, hexadecane, and octadecane were transformed completely; and 2 g/L <i>n</i>-hexadecane was degraded to undetectable levels within 72 h. Two putative alkane-degrading genes (gene 3623 and gene 4712) were characterized and our results indicated that their gene products were rate-limiting enzymes involved in the synergetic catabolism of C₁₂–C₁₆ alkanes. On the basis of bioinformatics and transcriptional analysis, two P450 monooxygenases, along with a putative AlmA-like oxygenase, were examined. Genetically defective mutants lacking the characteristic alkane hydroxylase failed to degrade <i>n</i>-octadecane, thereby suggesting a different catalytic mechanism for the microbial transformation of alkanes with chain lengths over C₁₈.</p>