Investigations on anaerobic degradation of protocatechuate by denitrifying and by iron-reducing bacteria

SummaryIn this thesis, anaerobic degradation of protocatechuate by the denitrifying bacterium Thauera aromatica strain AR-1 has been investigated. Enrichment cultures of bacteria which degrade protocatechuate, alpha-resorcylate or gentisate with ferric iron as electron acceptor can be used for further investigations on the anaerobic degradation of these dihydroxybenzoates.The degradation of protocatechuate by Thauera aromatica AR-1 is probably introduced by activation of protocatechuate with CoA. Benzoyl-CoA-reductase could be detected by immuno-blots in cells grown on protocatechuate or benzoate, but not in cells grown on alpha-resorcylate.During degradation of protocatechuate by dense cell-suspensions, accumulation of a not yet identified intermediate could be observed. The HPLC-peak of this intermediate decreases during the course of the experiment. In growing cultures, darkening of culture-supernatant and of cells could be observed.One culture enriched on protocatechuate and amorphous ferric-hydroxide is in the second isolation-step. The enrichment culture reduces ferric-iron during growth on protocatechuate as sole energy- and carbon-source. Enrichments on alpha-resorcylate and on gentisate have not been further pursued.The strains Geobacter sulfurreducens DFR1 and DFR2, Geobacter metallireducens, the cultures 3-2-A, 3-3-D, FON II, H2M II and AcMN II could not grow on protocatechuate, alpha-resorcylate or gentisate with amorphous ferric-hydroxide as electron-acceptor. Geobacter metallireducens could not grow on these substrates with ferric-citrate as electron-acceptor. Only with gentisate as growth-substrate ferrous-iron concentrations increased slightly