Degradation of Aromatic Compounds by Nonsulfur Purple Bacteria

摘要

In recent years, it has become evident that nonsulfur purple bacteria use a muchwider range of lignin-derived monomers for photosynthetic and aerobic growth than was previously suspected. While aerobic attack on the benzene ring appears to follow patterns common to aerobic pseudomonads, the anaerobic pathway is radically different, and the reductive attack on the ring, first suggested for Rhodopseudomanas palustris growing on benzoate, has now become firmly established. Coenzyme A thioesters are involved in removal of sidechains from complex aromatic acids prior to attack on the ring itself, and also at all stages of degradation of the nucleus up to and including ring opening. Probable intermediates in the ring reduction reactions have been identified both in vivo and in vitro, but characterization of the enzymes and cofactors involved has yet to be achieved. Two aromatic acid CoA ligases have been purified and the corresponding genes cloned and sequenced. A regulatory gene involved in expression of the ligase needed for 4-hydroxybenzoate activation has also been identified and belongs to the cyclic AMP receptor protein family of transcriptional activators.