Salicylate Stimulates the Degradation of High-Molecular Weight Polycyclic Aromatic Hydrocarbons by Pseudomonas saccharophila P15

Pseudomonas saccharophila P15 was isolated from soil contaminated with polycyclic aromatic hydrocarbons (PAH) and previously was reported to degrade a variety of low- and high-molecular weight PAH. Strain P15 grows on phenanthrene by a known pathway in which salicylate is an intermediate. Preincubation with phenanthrene and downstream intermediates through salicylate stimulated PAH dioxygenase activity and initial rates of phenanthrene removal, suggesting that salicylate is the inducer of these activities. Salicylate also greatly enhanced initial rates of removal of fluoranthene, pyrene, benz[a]anthracene, chrysene, and benzo[a]pyrene, high-molecular weight substrates that strain P15 does not use for growth. The specific rate of removal of benzo[a]pyrene was at least 2 orders of magnitude lower than that of the four-ring compounds and nearly 5 orders of magnitude lower than that of phenanthrene. The mineralization of phenanthrene, benz[a]anthracene, chrysene, and benzo[a]pyrene was stimulated by preincubation with phenanthrene or salicylate, although significant mineralization of phenanthrene, benz[a]anthracene, and chrysene occurred in uninduced cultures. Further experiments with chrysene indicated that chrysene does not appear to induce its own mineralization. Our results suggest that P. saccharophila P15 expresses a low level of constitutive PAH metabolism which is inducible to much higher levels and that high-molecular weight PAH metabolism by this organism is induced by the low-molecular weight substrate phenanthrene and by salicylate.