Rectinema cohabitans gen. nov., sp. nov., a rod-shaped spirochaete isolated from an anaerobic naphthalene-degrading enrichment culture.

The anaerobic, non-motile strain HMT was isolated from the naphthalene-degrading, sulfate-reducing enrichment culture N47. For 20 years, strain HMT has been a stable member of culture N47 although it is neither able to degrade naphthalene nor able to reduce sulfate in pure culture. The highest similarity of the 16S rRNA gene sequence of strain HMT (89 %) is with a cultivated member of the family Spirochaetaceae, Treponema caldariumstrain H1T (=DSM 7334T), an obligately anaerobic, thermophilic spirochaete isolated from cyanobacterial mat samples collected at a freshwater hot spring in Oregon, USA. In contrast to this strain and the majority of spirochaete species described, strain HMT showed a rod-shaped morphology. Growth occurred at temperatures between 12 and 50 °C (optimum 37 °C) but the isolate was not able to grow at 60 °C. The strain fermented various sugars including d-glucose, d-fructose, lactose and sucrose. Addition of 0.1 % (w/v) yeast extract or 0.1 % (w/v) tryptone to the culture medium was essential for growth and could not be replaced by either the vitamin solutions tested or by 0.1 % (w/v) peptone or 0.1 % (w/v) casamino acids. The DNA G+C content of the isolate was 51.5 mol%. The major fatty acids were C14 : 0, C18 : 1ω13c, C16 : 1ω9t, C16 : 1ω11c and C16 : 1ω9c. Based on the unique morphology and the phylogenetic distance from the closest cultivated relative, a novel genus and species, Rectinema cohabitans gen. nov., sp. nov., is proposed. The type strain is strain HMT (=DSM 100378T=JCM 30982T).

Anaerobic Degradation of Benzene and Polycyclic Aromatic Hydrocarbons.

Aromatic hydrocarbons such as benzene and polycyclic aromatic hydrocarbons (PAHs) are very slowly degraded without molecular oxygen. Here, we review the recent advances in the elucidation of the first known degradation pathways of these environmental hazards. Anaerobic degradation of benzene and PAHs has been successfully documented in the environment by metabolite analysis, compound-specific isotope analysis and microcosm studies. Subsequently, also enrichments and pure cultures were obtained that anaerobically degrade benzene, naphthalene or methylnaphthalene, and even phenanthrene, the largest PAH currently known to be degradable under anoxic conditions. Although such cultures grow very slowly, with doubling times of around 2 weeks, and produce only very little biomass in batch cultures, successful proteogenomic, transcriptomic and biochemical studies revealed novel degradation pathways with exciting biochemical reactions such as for example the carboxylation of naphthalene or the ATP-independent reduction of naphthoyl-coenzyme A. The elucidation of the first anaerobic degradation pathways of naphthalene and methylnaphthalene at the genetic and biochemical level now opens the door to studying the anaerobic metabolism and ecology of anaerobic PAH degraders. This will contribute to assessing the fate of one of the most important contaminant classes in anoxic sediments and aquifers.