Roles of the meta- and the ortho-Cleavage Pathways for the Efficient Utilization of Aromatic Hydrocarbons by Sphingomonas yanoikuyae B1

Catabolic pathways for the degradation of various aromatics by Sphingomonas yanoikuyae B1 are intertwined, joining at the level of substituted benzoates, which are further degraded via ring cleavage reactions. The mutant strain EK497, which was constructed by deleting a large DNA region containing most of the genes for biphenyl, naphthalene, m-xylene, and m-toluate degradation, was unable to grow on all of the aromatics tested except for benzoate as the sole source of carbon and energy. S. yanoikuyae EK497 was found to possess only catechol ortho-ring cleavage activity due to deletion of the genes for the meta-cleavage pathway. Wild-type S. yanoikuyae B1 grown on benzoate has both catechol orthoand meta-cleavage activity. However, m-xylene and m-toluate, which are metabolized through methylbenzoate, and biphenyl, which is metabolized through benzoate, induce only the meta-cleavage pathway, suggesting the presence of a substrate-dependent induction mechanism.