Physiology and taxonomy of phenol-degrading denitrifying bacteria

Phenol is both a natural and a manmade aromatic compound. Because of the widespread occurrence of phenol, microorganisms capable of degrading this compound can be found in many environments. The pathways for aerobic phenol degradation are well established and many aerobic phenol-degrading bacteria have been isolated. Phenol degradation under anaerobic conditions is less well understood, and only few pure cultures of anaerobic phenol-degrading microorganisms have been described so far. In this study, several new denitrifying bacteria which can use phenol as their sole source of carbon and energy were isolated and characterized. Their taxonomic position was determined by analysis of the cell membrane fatty acid composition as well as by 16S ribosomal DNA gene sequence analysis. The new phenol-degrading strains are affiliated with the recently described genus Azoarcus. The physiology of one of the strains, PH002, was studied in detail. Cells of this strain flocculate during stationary phase. Flocculation is most likely caused by increased cell surface hydrophobicity and increased cohesive forces between cells. This organism also accumulates significant amounts of the storage polymer poly-{dollar}beta{dollar}-hydroxybutyrate. Additionally, the phenol and para-cresol metabolism of strain PH002 was investigated. Results indicate that the first step in anaerobic degradation of phenol is carboxylation to 4-hydroxybenzoate. This finding confirms reports in the literature.; p-Cresol degradation is initiated by hydroxylation of the methyl group. The p-cresol methyl hydroxylase activity of strain PH002 was partially purified and analyzed in vitro.; Finally, contaminants such as benzene and toluene are known to sorb to organic matter in soil. Sorption can significantly reduce the availability of these compounds for biodegradation. Because soil bacteria are a part of the soil organic matter, they are likely to contribute to the total sorption of contaminants in soils. In comparison to several other bacterial species, strain PH002 was shown to have a pronounced capacity to sorb toluene. Calculations based on results of these sorption studies indicate that bacterial biosorption may contribute up to 50% to the total sorption of environmental contaminants in soil.