Biodegradation of nitroaromatic compounds: Interrelationships between catabolism of nitrophenols and nitrobenzene

This thesis describes biological mechanisms of degradation of nitroaromatic compounds and more specifically the interrelationships between biodegradative metabolism of nitrophenols (NPs) and nitrobenzene (NB). An initial study on conversion of NB to NPs by electron beam provided the impetus for the biodegradative study.; Three groups of bacteria were isolated from the mixed culture after intensively sub-culturing on the NPs as the growth substrates. Strains of group A ( 2NP−3NP−4NP+) were Pseudomonas species, which grew on 4-NP, but not on 2-NP or 3-NP. Strains of group B (2NP+3NP+4NP −) were also Pseudomonas species, which grew on 2-NP and 3-NP, but not on 4-NP. Strains of group C ( 2NP−3NP+4NP−), grew on 3-NP, but not on 2-NP or 4-NP. One of the two strain types was identified as Variovorax paradoxus. Degradation of 2- and 4-NP produced nitrite. Only 3-NP-grown cells of strains of Group B and C, degraded NB and produced ammonia from both NB and 3-NP.; Pseudomonas putida 2NP8, a typical strain of group B, was investigated for mechanism and interrelationship of NB and NP metabolism. 2-NP was degraded with production of nitrite. Degradation of 3-NP resulted in the formation of ammonia. Cells grown on 2-NP did not degrade NB.; Biotransformation products of hydroxylaminobenzene and aminophenol, produced by 3-NP-grown cells of Pseudomonas putida 2NP8, were characterized. All metabolites were also found in the NB transformation medium, and this demonstrated that they were metabolites of NB transformation via hydroxylaminobenzene.; The degradation pathway of 3-NP in P. putida 2NP8 was postulated, based on NB transformation products. This mechanism suggested that 1,2,4-trihydroxylbenzene is the dioxygenase ring-cleavage substrate in 3-NP metabolism.; The 3-NP-grown cells of Pseudomonas putida 2NP8 had wide substrate range in metabolizing the nitroaromatic substrate through to ammonia production. When thirty nitroaromatic compounds were tested as substrates, all were quickly degraded except 4-NP, 2,4-di-NP, 2,4,6-tri-NP, 2-nitrobenzoic acid and 2-nitrofuran. Ammonia production from most of the nitroaromatic substrates appeared to be stoichiometric.; The 2-NP-induced enzyme system of Pseudomonas putida 2NP8 transforms 2-NP into nitrite and the 3-NP-induced system transforms 3-NP into ammonia. (Abstract shortened by UMI.)...