nitrogenase and resorcinol

The high resonance energy of the benzene ring is responsible for the relative resistance of aromatic compounds to biodegradation. Nevertheless, bacteria from nearly all physiological groups have been isolated which utilize aromatic growth substrates as the sole source of cell carbon and energy. The enzymatic dearomatization of the benzene nucleus by microorganisms is accomplished in two different manners. In aerobic bacteria the aromatic ring is dearomatized by oxidation, catalyzed by oxygenases. In contrast, anaerobic bacteria attack the aromatic ring by reductive steps. Key intermediates in the anaerobic aromatic metabolism are benzoyl-CoA and compounds with at least two meta-positioned hydroxyl groups (resorcinol, phloroglucinol and hydroxyhydroquinone). In facultative anaerobes, the reductive dearomatization of the key intermediate benzoyl-CoA requires a stoichiometric coupling to ATP hydrolysis, whereas reduction of the other intermediates is readily achieved with suitable electron donors. Obligately anaerobic bacteria appear to use a totally different enzymology for the reductive dearomatization of benzoyl-CoA including selenocysteine- and molybdenum- containing enzymes.

Topics: Adenosine Triphosphate; Bacteria, Anaerobic; Benzene; Coenzyme A Ligases; Hydrolysis; Hydroquinones; Nitrogenase; Oxidoreductases; Phloroglucinol; Resorcinols

Azotobacter chroococcum MH1 was grown in a mannitol and nitrogen free medium supplemented with p-hydroxybenzoic acid, resorcinol, catechol or vanillic acid as a sole carbon source. Growth and nitrogenase activity of p-hydroxybenzoic acid were supported by 8, 6 and 4 mM of p-hydroxybenzoic acid, resorcinol and catechol, respectively. The generation time of 1.71 h in p-hydroxybenzoic acid did not differ from a generation time of 1.64 h, when grown in mannitol. The compound p-hydroxybenzoic acid was utilized rapidly. However, the decomposition of other phenolic compounds tested proceeded slowly. These results suggested that phenolic compounds released during biodegradation of plant wastes could be utilized as carbon sources for both growth and nitrogen fixation of Azotobacter chroococcum.

Topics: Azotobacter; Bacterial Proteins; Biodegradation, Environmental; Catechols; Cell Division; Nitrogenase; Parabens; Phenols; Resorcinols; Soil Microbiology; Vanillic Acid