Cross Induction of 4-Nitrobenzoate and 4-Aminobenzoate Degradation by Burkholderia Cepacia Strain PB4

Abstract

A variety of industrial activities (production of explosives, pesticides, polymers, etc.) have introduced into the environment several nitroaromatic compounds (NACs) which are toxic and recalcitrant to biodegradation by the microorganisms commonly found in nature. The most common reaction undergone by these compounds is the reduction of the nitro group, the aminoaromatic compound (AAC) then produced generally not being further degraded. Due to this ubiquitous nitroreductase activity, AACs are often found together with NACs at contaminated sites or effluents. An efficient bioremediation process should combine treatment of both classes of compounds. Burkholderia cepacia, isolated on 4-aminobenzoate as sole source of C, N and energy, was found to be also able to grow on 4-nitrobenzoate. This pure strain has thus the property to mineralize both a NAC and the corresponding AAC. Metabolic pathway studies with B. cepacia have shown that it mineralizes 4-nitrobenzoate and 4aminobenzoate through independent but converging pathways. Curiously, 4-nitrobenzoate degradation was induced by 4-aminobenzoate and vice-versa. The degradation of an equimolar mixture of these two compounds (1 mM each) by washed cells of B. cepacia grown on 4nitrobenzoate, 4-aminobenzoate or glucose was studied in batch cultures. When induced on either 4-nitrobenzoate or 4-aminobenzoate, B. cepacia metabolized the inducer faster than the second compound. When grown on glucose, the microorganism mineralized both compounds simultaneously after a short lag. No diauxic growth was observed but rather a normal growth curve. The two pathways of degradation were found to be working simultaneously and such an organism might be appropriate for the bioremediation of a NAC, in this case 4-nitrobenzoate, together with its corresponding AAC, 4-aminobenzoate.