Two distinct pathways for anaerobic degradation of aromatic compounds in the denitrifying bacterium Thauera aromatica strain AR-1.
Denitrifying bacteria degrade many different aromatic compounds anaerobically via the well-described benzoyl-CoA pathway. We have shown recently that the denitrifiers Azoarcus anaerobius and Thauera aromatica strain AR-1 use a different pathway for anaerobic degradation of resorcinol (1,3-dihydroxybenzene) and 3,5-dihydroxybenzoate, respectively. Both substrates are converted to hydroxyhydroquinone (1,2,4-trihydroxybenzene). In the membrane fraction of T. aromatica strain AR-1 cells grown with 3,5-dihydroxybenzoate, a hydroxyhydroquinone-dehydrogenating activity of 74 nmol min(-1)(mg protein)-1 was found. This activity was significantly lower in benzoate-grown cells. Benzoate-grown cells were not induced for degradation of 3,5-dihydroxybenzoate, and cells grown with 3,5-dihydroxybenzoate degraded benzoate only at a very low rate. With a substrate mixture of benzoate plus 3,5-dihydroxybenzoate, the cells showed diauxic growth. Benzoate was degraded first, while complete degradation of 3,5-dihydroxybenzoate occurred only after a long lag phase. The 3,5-dihydroxybenzoate-oxidizing and the hydroxyhydroquinone-dehydrogenating activities were fully induced only during 3,5-dihydroxybenzoate degradation. Synthesis of benzoyl-CoA reductase appeared to be significantly lower in 3,5-dihydroxybenzoate-grown cells as shown by immunoblotting. These results confirm that T. aromatica strain AR-1 harbors, in addition to the benzoyl-CoA pathway, a second, mechanistically distinct pathway for anaerobic degradation of aromatic compounds. This pathway is inducible and subject to catabolite repression by benzoate.
Philipp
B
B
Fakultät für Biologie, Universität Konstanz, Germany. Bodo.Philipp@uni-konstanz.de
Schink
B
B
D000214:Acyl Coenzyme A / Q000378:metabolism; D001565:Benzoates / Q000378:metabolism*; D001673:Biodegradation, Environmental; D004790:Enzyme Induction; D015964:Gene Expression Regulation, Bacterial; D006873:Hydroquinones / Q000378:metabolism; D062385:Hydroxybenzoates / Q000378:metabolism*; D009566:Nitrates / Q000378:metabolism*; D010084:Oxidation-Reduction; D010088:Oxidoreductases / Q000378:metabolism; D044925:Oxidoreductases Acting on CH-CH Group Donors; D020628:Thauera / Q000254:growth & development / Q000378:metabolism*
D000214:Acyl Coenzyme A; D001565:Benzoates; D006873:Hydroquinones; D062385:Hydroxybenzoates; D009566:Nitrates; C013038:hydroxyhydroquinone; C037817:benzoyl-coenzyme A; D010088:Oxidoreductases; D044925:Oxidoreductases Acting on CH-CH Group Donors; C109030:benzoyl-coenzyme A reductase (dearomatizing)