Phenol degradation under methanogenic conditions has long been studied, but the anaerobes responsible for the degradation reaction are still largely unknown. An anaerobe, designated strain UI T , was isolated in a pure syntrophic culture. This isolate is the first tangible, obligately anaerobic, syntrophic substrate-degrading organism capable of oxidizing phenol in association with an H 2 -scavenging methanogen partner. Besides phenol, it could metabolize p-cresol, 4-hydroxybenzoate, isophthalate, and benzoate. During the degradation of phenol, a small amount of 4-hydroxybenzoate (a maximum of 4 M) and benzoate (a maximum of 11 M) were formed as transient intermediates. When 4-hydroxybenzoate was used as the substrate, phenol (maximum, 20 M) and benzoate (maximum, 92 M) were detected as intermediates, which were then further degraded to acetate and methane by the coculture. No substrates were found to support the fermentative growth of strain UI T in pure culture, although 88 different substrates were tested for growth. 16S rRNA gene sequence analysis indicated that strain UI T belongs to an uncultured clone cluster (group TA) at the family (or order) level in the class Deltaproteobacteria. Syntrophorhabdus aromaticivorans gen. nov., sp. nov., is proposed for strain UI T , and the novel family Syntrophorhabdaceae fam. nov. is described. Peripheral 16S rRNA gene sequences in the databases indicated that the proposed new family Syntrophorhabdaceae is largely represented by abundant bacteria within anaerobic ecosystems mainly decomposing aromatic compounds.Phenols and phthalate isomers are among the most widely used chemicals and are often found in industrial wastewaters in abundance. These chemicals are known to be inhibitors for the growth of microorganisms in biological treatment processes and are regarded as priority pollutants on the U.S. Environmental Protection Agency list (19,38). Phenol has long been known to be degraded anaerobically in the methanogenic environment (20, 43). Methanogenic degradation of phenol is significant considering the wastewater treatment processes of industrial waste chemicals and biogeochemistry of naturally occurring phenolic compounds in deep subsurface environments, such as an oil reservoir. However, despite the tremendous effort to search for phenol degraders in such environments, only a few examples are known. To date, only one species, Cryptanaerobacter phenolicus, has been isolated and characterized as an anaerobe able to metabolize phenol under methanogenic conditions (16). The organism is an anaerobic bacterium that can transform phenol into benzoate in the presence of as-yet-unidentified electron donors. However, no organisms that are genuinely capable of utilizing phenol as the sole energy source under methanogenic conditions have been isolated so far.Recently, the enrichment and identification of mesophilic phthalate isomer-degrading bacteria from methanogenic sludges treating wastewater from the manufacture of terephthalic and isophthalic acids were reported (29). Thro...

The classical perception of members of the gram-positive Desulfotomaculum cluster I as sulfate-reducing bacteria was recently challenged by the isolation of new representatives lacking the ability for anaerobic sulfate respiration. For example, the two described syntrophic propionate-oxidizing species of the genus Pelotomaculum form the novel Desulfotomaculum subcluster Ih. In the present study, we applied a polyphasic approach by using cultivation-independent and culturing techniques in order to further characterize the occurrence, abundance, and physiological properties of subcluster Ih bacteria in low-sulfate, methanogenic environments. 16S rRNA (gene)-based cloning, quantitative fluorescence in situ hybridization, and real-time PCR analyses showed that the subcluster Ih population composed a considerable part of the Desulfotomaculum cluster I community in almost all samples examined. Additionally, five propionate-degrading syntrophic enrichments of subcluster Ih bacteria were successfully established, from one of which the new strain MGP was isolated in coculture with a hydrogenotrophic methanogen. None of the cultures analyzed, including previously described Pelotomaculum species and strain MGP, consumed sulfite, sulfate, or organosulfonates. In accordance with these phenotypic observations, a PCR-based screening for dsrAB (key genes of the sulfate respiration pathway encoding the alpha and beta subunits of the dissimilatory sulfite reductase) of all enrichments/(co)cultures was negative with one exception. Surprisingly, strain MGP contained dsrAB, which were transcribed in the presence and absence of sulfate. Based on these and previous findings, we hypothesize that members of Desulfotomaculum subcluster Ih have recently adopted a syntrophic lifestyle to thrive in low-sulfate, methanogenic environments and thus have lost their ancestral ability for dissimilatory sulfate/sulfite reduction.Members of Desulfotomaculum cluster I have been generally known as gram-positive, spore-forming, sulfate-reducing bacteria (50, 56) and have frequently been found in various anoxic environments, such as sediments, rice paddy soil, human feces, and anaerobic sludges (for examples, see references 21, 42, 56, 57). The genus Desulfotomaculum includes over 20 validly described mesophilic and thermophilic species, all of which share the ability to oxidize various organic substances, like shortchain fatty acids, alcohols, and aromatic compounds with sulfate as a terminal electron acceptor (56). Due to these physiological traits, members of Desulfotomaculum cluster I have been considered important in sulfidogenic, anoxic environments, where they play crucial roles in the degradation of organic compounds, as well as in the biogeochemical cycling of sulfur (56).On the basis of comparative 16S rRNA gene sequence analysis, Desulfotomaculum cluster I was considered to be comprised of seven well-separated subclusters, Ia to Ig (27,50,52,57). Although it has been argued that each subcluster could be treated taxonomically as an individual...