scpA, a new salicylate hydroxylase gene localized in salicylate/caprolactam degradation plasmids

Both caprolactams and salicylate biodegradation by Pseudomonas salicylate/caprolactam degraders are controlled by large conjugative plasmids (SAL/CAP). Some of these plasmids have been assigned to the P-7 incompatibility group. The new salicylate 1-hydroxylase gene (scpA) has been detected in SAL/CAP plasmids and partially sequenced. The scpA gene was equally related to the closest homolog genes nahG (NAH7), salA (P. reinekei MT1), and nahU (pND6-1); however, the identity rate did not exceed 72–74%. The synthesis of salicylate 1-hydroxylase ScpA was not induced by salicylate. This enzyme had wide substrate specificity and exhibited the highest specific activity toward 4-methylsalicylate and nonsubstituted salicylate substrates. Furthermore, conjugative pseudomonads’ plasmids of salicylate degradation without the classical nah2 operon, which harbors only salicylate 1-hydroxylase gene nahU have been described for the first time.