Isolation and Characterization of a New Denitrifying Spirillum Capable of Anaerobic Degradation of Phenol

Abstract

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...

Characterization of a Spontaneous Nonmagnetic Mutant ofMagnetospirillum gryphiswaldenseReveals a Large Deletion Comprising a Putative Magnetosome Island

“…Thus, it can be inferred that most of the gene functions specifically required for magnetite synthesis are organized within a large genomic supercluster, which might be tentatively termed a magnetosome island, and putatively have been distributed by horizontal gene transfer. A growing number of bacterial isolates from different environments can be clearly identified as Magnetospirillum species based on 16S rRNA sequence analysis and morphological and physiological characteristics but lack the ability to form magnetosomes (10,45). It will be interesting to see if these nonmagnetic magnetospirilla are distinguished from their magnetic relatives by the absence of the magnetosome island.…”

Anaerobic Degradation of Aromatic Compounds byMagnetospirillumStrains: Isolation and Degradation Genes

“…Their quinone profiles and G þ C content are consistent with this result. This shows it is not a single strain 11) but a group of bacteria that belong to this phylogenetic position of Proteobacteria and can degrade aromatic compounds under anaerobic denitrifying conditions. Recently, Barragan et al predicted anaerobic benzoate degradation by M. magnetotacticum MS-1 from its genome sequence and proved it, 30) supporting this conclusion.…”

“…In a previous paper, 11) we reported the isolation of an anaerobic phenol-degrading strain most closely related to the genus Magnetospirillum. This was the first report of a denitrifying strain of Proteobacteria degrading aromatic compounds.…”

Phenylphosphate Carboxylase: a New C-C Lyase Involved in Anaerobic Phenol Metabolism in Thauera aromatica

“…Furthermore, a very interesting 4-hydroxyphenylacetate decarboxylase which belongs to the glycine radical enzyme family was found in Clostridium difficile (56). Other carboxylases have not been studied in more detail, although anaerobic metabolism of phenol or chlorophenols (4,9,19,41,(57)(58)(59)(60)(61)(62)(65)(66)(67) and other phenolic or anilinic compounds is widespread. o-Cresol (2-methylphenol) (8,9,53), m-cresol (3-methylphenol) (49,51), hydroquinone (1,4-dihydroxybenzene) (28,29), catechol (1,2-dihydroxybenzene) (27), and aniline (aminophenol) (55) are metabolized by pure cultures of denitrifying and sulfate-reducing bacteria and consortia of fermenting bacteria, and the process involves carboxylation of the aromatic ring para or ortho to the hydroxy or amino substituent.…”