Abstract.With resorcinol as sole source of energy and organic carbon, two stains of gram-negative, nitratereducing bacteria were isolated under strictly anaerobic conditions. Strain LuBResl was facultatively anaerobic and catalase-and superoxide dismutase-positive. This strain was affiliated with Alcaligenes denitrificans on the basis of substrate utilization spectrum and peritrichous flagellation. Strain L u F R e s l could grow only under anaerobic conditions with oxidized nitrogen compounds as electron acceptor. Cells were catalase-negative but superoxide dismutase-positive. Since this strain was apparently an obligate nitrate reducer, it could not be grouped with any existing genus. Resorcinol was completely oxidized to CO2 by both strains. Neither an enzyme activity reducing or hydrolyzing the resorcinol molecule, nor an acyl-CoA-synthetase activating resorcylic acids or benzoate was detected in cell-free extracts of cells grown with resorcinol. In dense cell suspensions, both strains produced a compound which was identified as 5-oxo-2-hexenoic acid by mass spectrometric analysis. This would indicate a direct, hydrolytic cleavage of the resorcinol nucleus without initial reduction.

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Abstract. Anaerobic degradation of hydroquinone was studied with the fermenting bacterium strain HQG61. The rate of hydroquinone degradation by dense cell suspensions was dramatically accelerated by addition of NaHCO3. During fermentation of hydroquinone in the presence of 14C-Na2CO3 benzoate was formed as a labelled product, indicating an initial ortho-carboxylation of hydroquinone to gentisate. Gentisate was activated to the corresponding CoA-ester in a CoA ligase reaction at a specific activity of 0.15 gmol x rain-1 x mg protein-1. Gentisyl-CoA was reduced to benzoyl-CoA with reduced methyl viologen as electron donor by simultaneous reductive elimination of both the ortho and meta hydroxyl group. The specific activity of this novel gentisyl-CoA reductase was 17 nmol x rain-1 x mg protein-1. Further degradation to acetate was catalyzed by enzymes which occur also in other bacteria degrading aromatic compounds via benzoyl-CoA.

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