MICROBIAL PHOTODEGRADATION OF AMINOARENES METABOLISM OF 2-AMINO-4-NITROPHENOL BY RHODOBACTER-CAPSULATUS

The phototrophic bacterium Rhodobacter capsulatus photoreduces 2,4-din itrophenol to 2-amino-4-nitrophenol, which is further metabolized by a n aerobic pathway that is also light-dependent. The catabolism of 2-am ino-4-nitrophenol requires O, and the presence of alternative carbon ( C) and nitrogen (N) sources, preferably acetate and ammonium. Rhodobac ter capsulatus B10, a bacterium unable to assimilate nitrate, releases negligible amounts of nitrite when growing with 2-amino-4-nitrophenol , thus suggesting that an oxygenase, nitrite-producing activity is not involved in the metabolization of the compound. The diazotrophic grow th of R. capsulatus increases in the presence of 2-amino-4-nitrophenol , but growth with ammonium is clearly inhibited by the compound. Mutan t strains of R. capsulatus B10, which are affected in nifHDK, nifR1, o r nifR4 genes, unable to fix dinitrogen, do not grow with 2-amino-4-ni trophenol as the sole N source. This indicates that the compound canno t be used as a N source. The nif mutants degrade 2-amino-4-nitrophenol to the same extent as the wild-type in the presence of ammonium. The compound is not used as a C source by the bacterium, either. Aromatic stable intermediates, such as 2,4-diaminophenol or 4-nitrocatechol, ar e not detectable in microaerobic cultures of R. capsulatus growing wit h 2,4-dinitrophenol or 2-amino-4-nitrophenol.