Induction of aromatic catabolic activity in Sphingomonas aromaticivorans strain F199

Enzyme induction studies with Sphingomonas aromaticivorans F199 demonstrate d that both toluene and naphthalene induced expression of both naphthalene and toluene catabolic enzymes. However, neither aromatic compound induced e xpression of all the enzymes required for complete mineralization of either naphthalene or toluene, Activity measurements in combination with gene seq uence analyses indicate that growth on either aromatic substrate in the abs ence of the other is, therefore, sub-optimal and is predicted to lead to th e build-up of metabolites due to imbalance in toluene or naphthalene catabo lic enzyme activities. Growth on toluene may be further inhibited by the co -expression of two toluene catabolic pathways, as predicted from gene seque nce analyses. One of these pathways may potentially result in the formation of a dead-end intermediate, possibly benzaldehyde. In contrast, either p-c resol or benzoate can support high levels of growth. Analyses of promoter r egion sequences on the F199 aromatic catabolic plasmid, pNL1, suggest that additional regulatory events are modulated through the interaction of BphR with Sigma54 type promoters and through the binding of a regulator upstream of p-cresol catabolic genes and xylM. We hypothesize that the unusual gene clustering in strain F199 is optimized for simultaneous degradation of mul tiple aromatic compound classes, possibly in response to the heterogeneous composition of aromatic structures in the fossil organic matter present in the deep Atlantic Coastal Plain sediments from which this bacterium was iso lated.