Critical steps in degradation of chloroaromatics by rhodococci I. Initial enzyme reactions involved in catabolism of aniline, phenol and benzoate by Rhodococcus sp. An 117 and An 213

Two bacterial isolates (i.e. strains An 117 and An 213) capable of growing with aniline, phenol as well as benzoate as the sole carbon and energy source were studied with respect to (i) their taxonomic position, (ii) the enzyme reactions which initiate catabolism of the respective aromatic compounds, and (iii) the general type of regulation of the respective enzymes. Both isolates were established to be representatives of the actinomycete‐genus Rhodococcus . Experiments with resting cells and cell‐free extracts, respectively, revealed that in the two strains under study catabolism of each of the unsubstituted aromatic compounds occurs via the β‐ketoadipate pathway (with catechol as the central metabolite) due to the action of inducible enzymes. Although being potent inducers of the ring‐cleaving catechol 1,2‐dioxygenase in strains An 117 and An 213, all of the monochlorinated derivatives of aniline, phenol and benzoate, respectively, failed to support cell growth of the organisms. Cis, cis ‐muconic acid proved to be non‐metabolizable by resting An 117 and An 213 cells, although substantial (inducible) muconate cycloisomerase activity was detectable in crude extracts prepared from the respective cell preparations. NADPH‐depending phenol hydroxylase activity could be demonstrated in crude extracts from phenol‐grown An 117 and An 213 cells. Evidence is presented that in both Rhodococcus strains under study substantial de novo synthesis of at least the initial aromatics‐oxygenating enzymes can be induced by phenol and aniline, respectively, even in the presence of either succinate (An 117) or acetate (An 213) which are known to be ortho ‐pathway catabolites.