Identification and functional analysis of the genes for naphthalenesulfonate catabolism by Sphingomonas xenophaga BN6

Abstract

Sphingomonas xenophagaBN6 degrades various (substituted) naphthalenesulfonates to the corresponding (substituted) salicylates. A gene cluster was identified on the plasmid pBN6 which coded for several enzymes participating in the degradative pathway for naphthalenesulfonates. A DNA fragment of 16 915 bp was sequenced which contained 17 ORFs. The genes encoding the 1,2-dihydroxynaphthalene dioxygenase, 2-hydroxychromene-2-carboxylate isomerase, and 2′-hydroxybenzalpyruvate aldolase of the naphthalenesulfonate pathway were identified on the DNA fragment and the encoded proteins heterologously expressed inEscherichia coli. Also, the genes encoding the ferredoxin and ferredoxin reductase of a multi-component, ring-hydroxylating naphthalenesulfonate dioxygenase were identified by insertional inactivation. The identified genes generally demonstrated the highest degree of homology to enzymes encoded by the phenanthrene-degrading organismSphingomonassp. P2, or the megaplasmid pNL1 of the naphthalene- and biphenyl-degrading strainSphingomonas aromaticivoransF199. The genes ofS. xenophagaBN6 participating in the degradation of naphthalenesulfonates also shared the same organization in three different transcriptional units as the genes involved in the degradation of naphthalene, biphenyl, and phenanthrene previously found inSphingomonassp. P2 andS. aromaticivoransF199. The genes were flanked inS. xenophagaBN6 by ORFs which specify proteins that show the highest homologies to proteins of mobile genetic elements.