MICROBIAL TRANSFORMATION OF NITROAROMATIC COMPOUNDS UNDER ANAEROBIC CONDITIONS

The transformation of several mono- and dinitroaromatic compounds (tes ted at 50-200 muM) by methanogenic bacteria, sulphate-reducing bacteri a and clostridia was studied. Some of the nitroaromatics tested were t ransformed chemically by 1.5 mm quantities of culture media reducing a gents, like cysteine or sulphide. This abiotic reduction occurred at t he o-nitro-groups preferentially. Nitrophenols, p-nitroaniline and p-n itrobenzoic acid were completely transformed biologically into the cor responding amino derivatives. The nitroaromatics were transformed by a ll of the bacterial strains tested. While growing cells of sulphate-re ducing bacteria and Clostridium spp. carried out nitroreduction, metha nogen cells lysed in the presence of nitroaromatics. Nevertheless thes e culture suspensions converted nitroaromatics to the corresponding am ino derivatives. This was also confirmed by crude cell extracts of met hanogenic bacteria. The rate of nitroreduction by sulphate-reducing ba cteria depended on the electron donors supplied and the cell density, with molecular hydrogen being the most effective donor of reducing equ ivalents. The toxicity of p-nitrophenol to some of the organisms teste d depended on the concentration of the nitroaromatic compound and the type of organism.