Two kinds of phenol-degrading denitrifying bacteria, Azoarcus sp. strain CC-11 and spiral bacterial strain CC-26, were isolated from the same enrichment culture after 1 and 3 years of incubation, respectively. Both strains required ferrous ions for growth, but strain CC-26 grew better than strain CC-11 grew under ironlimited conditions, which may have resulted in the observed change in the phenol-degrading bacteria during the enrichment process. Strain CC-26 grew on phenol, benzoate, and other aromatic compounds under denitrifying conditions. Phylogenetic analysis of 16S ribosomal DNA sequences revealed that this strain is most closely related to a Magnetospirillum sp., a member of the ␣ subclass of the class Proteobacteria, and is the first strain of a denitrifying aromatic compound-degrading bacterium belonging to this group. Unlike previously described Magnetospirillum strains, however, this strain did not exhibit magnetotaxis. It grew on phenol only under denitrifying conditions. Other substrates, such as acetate, supported aerobic growth, and the strain exhibited microaerophilic features.Bacterial degradation of aromatic compounds under anaerobic conditions has been intensely studied, especially in the past decade. These reactions are of great interest, because unlike aerobic degradation by (di)oxygenases, alternative strategies are required, for example, to dearomatize and cleave a chemically stable benzene moiety without the use of molecular oxygen. Various kinds of bacteria or bacterial consortia are now known to degrade aromatic compounds under anaerobic conditions (9). In many cases, the compounds are converted into benzoyl coenzyme A (benzoyl-CoA) as a common central intermediate (peripheral pathways) and then degraded further into acetyl-CoA (benzoyl-CoA pathway) (8).Most denitrifying aromatic compound-degrading bacteria that have been isolated so far are Thauera (1) or Azoarcus (26) species which are members of the ␤ subclass of the class Proteobacteria (9). Bakker (3) and Khoury et al. (13) described spiral bacteria in mixed cultures that degraded phenol under denitrifying conditions but did not characterize these organisms. In this paper, we describe two isolates of denitrifying phenol-degrading bacteria obtained from the same enrichment culture during 3 years of incubation. A rod-shaped bacterium, strain CC-11, belongs to the genus Azoarcus, but the other isolate, which has spiral cells, is phylogenetically most closely related to strains belonging to the genus Magnetospirillum. The latter strain, designated CC-26, is the first example of a denitrifying aromatic compound-degrading bacterium that belongs to the ␣ subclass of the Proteobacteria. MATERIALS AND METHODS Enrichment and isolation.A bacterial consortium that degraded phenol under denitrifying conditions was enriched in a 2-liter jar fermentor (Mitsuwa Scientific Corp., Osaka, Japan) that was continuously fed with phenol as the sole carbon source. The enrichment medium was the medium of Tschech and Fuchs (24) containing phenol (1 mM), NaH...