ABSTRACT:

The substrate range of 2,4-dinitrotoluene (DNT) dioxygenase was investigated by measuringsubstrate-dependent O2 uptake and maximum growth (expressed in A600) on substrate-containingminimal medium. The control for each strain had no added particular substrate. Thefollowing aromatic compounds: catechol, a-naphthalene acetic acid, b-dimethylaminobenzaldehyde,3,4-dinitrosalicylic acid, p-nitrophenol, naphthanol, o-anisic acid, salicylic acid, toluene,and benzoic acid, were tried as possible substrates. Considering all substrates used,only p-nitrophenol showed zero oxygen uptake rate and zero growth. This indicates that itwas rather unlikely that p-nitrophenol is a substrate analog for 2,4-DNT. Catechol was clearlyused as a sole carbon source by both wild-type Escherichia. coli (JM103) and the dnt transformant(JS39). Using a-naphthalene acetic acid and b-dimethylaminobenzaldehyde as substratesresulted in DNT dioxygenase oxygen uptake rates of 11.8 and 14 lM/hr/mg protein,respectively. However, using both compounds as a carbon source, JS39 had twice thegrowth rate of E. coli JM103. For the remaining six substrates tested (3, 4-dinitrosalicylicacid, p-nitrophenol, o-anisic acid, salicylic acid, toluene, and benzoic acid), there appearedto be growth advantages for JS39 (even though the growth in the presence of substratewas less than the controls) suggesting a situation similar to that described for a-naphthaleneand b-dimethylaminobenzaldehyde above. Combining results from our assay withrespirometry and growth-based experiments will allow a better understanding of the biochemicalconsequences of these interactions. These results suggest that DNT dioxygenasegene, dntA carried by JS39, and those potential genes for substrates-degraded enzyme(s)system could have a common root.