OXIDATIVE PATHWAY FOR THE BIODEGRADATION OF NITROBENZENE BY COMAMONASSP STRAIN JS765

Previous studies have shown that the biodegradation of nitrobenzene by Pseudomonas pseudoalcaligenes JS45 proceeds by the reduction of nitro benzene through nitrosobenzene and hydroxylaminobenzene, followed by r earrangement to 2-aminophenol, which then undergoes meta ring cleavage , We report here the isolation of a Comamonas sp. that uses an oxidati ve pathway for the complete mineralization of nitrobenzene. The isolat e, designated strain JS765, uses nitrobenzene as a sole source of carb on, nitrogen, and energy, Nitrobenzene-grown cells oxidized nitrobenze ne, with the stoichiometric release of nitrite, Extracts of nitrobenze ne-grown JS765 showed high levels of catechol 2,3-dioxygenase activity that were not abolished by heating the cell extracts to 60 degrees C for 10 min, The ring cleavage product had an absorbance maximum at 375 nm, consistent, with that of 2-hydroxymuconic semialdehyde. Both NAD- dependent dehydrogenase and NAD-independent hydrolase activities towar ds 2-hydroxymuconic semialdehyde were induced in extracts of nitrobenz ene-grown cells. Catechol accumulated in the reaction mixture when cel ls preincubated with 3-chlorocatechol were incubated with nitrobenzene . Conversion of nitrobenzene to catechol by induced cells in the prese nce of 3-chlorocatechol and O-18(2), demonstrated the simultaneous inc orporation of two atoms of oxygen, which indicated that the initial re action was dioxygenation. The results indicate that the catabolic path way involves an initial dioxygenase attack on nitrobenzene with the re lease of nitrite and formation of catechol, which is subsequently degr aded by a meta cleavage pathway.