Versatile catechol dioxygenases in Sphingobium scionense WP01T.

ABSTRACT

The objective was to understand the roles of multiple catechol dioxygenases in the type strain Sphingobium scionense WP01T (Liang and Lloyd-Jones in Int J Syst Evol Microbiol 60413-416, 2010a) that was isolated from severely contaminated sawmill soil. The dioxygenases were identified by sequencing, examined by determining the substrate specificities of the recombinant enzymes, and by quantifying gene expression following exposure to model priority pollutants. Catechol dioxygenase genes encoding an extradiol xylE and two intradiol dioxygenases catA and clcA that are highly similar to sequences described in other sphingomonads are described in S. scionense WP01T. The distinct substrate specificities determined for the recombinant enzymes confirm the annotated gene functions and suggest different catabolic roles for each enzyme. The role of the three enzymes was evaluated by analysis of enzyme activity in crude cell extracts from cells grown on meta-toluate, benzoate, biphenyl, naphthalene and phenanthrene which revealed the co-induction of each enzyme by different substrates. This was corroborated by quantifying gene expression when cells were induced by biphenyl, naphthalene and pentachlorophenol. It is concluded that the ClcA and XylE enzymes are recruited in pathways that are involved in the degradation of chlorinated aromatic compounds such as pentachlorophenol, the XylE and ClcA enzymes will also play a role in degradation pathways that produce alkylcatechols, while the three enzymes ClcA, XylE and CatA will be simultaneously involved in pathways that generate catechol as a degradation pathway intermediate.