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

Abstract

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 phenanthrene by a sulfate‐reducing enrichment culture

“…Other members in culture TRIP1 include Spirochaetes, members of which (e.g., Spirochaetaceae) are often found in anaerobic cultures capable of degrading aromatic compounds and have been identified in sediment, ground-and freshwater samples. Their role of these Spirochaetes appears related to necromass fermentation, leading to a microbial loop recycling nutrients (Koelschbach et al, 2017;Dong et al, 2018).…”

Fermentative Spirochaetes mediate necromass recycling in anoxic hydrocarbon-contaminated habitats

“…Based on 16S rRNA gene sequence analysis, ~93% of the culture comprised a hitherto uncultured sulfate reducer Desulfobacterium strain N47 that has been shown to be responsible for naphthalene degradation [ 5 , 14 ]. The remainder of the enrichment culture mainly comprised a Spirochete, Rectinema cohabitans strain HM, which is neither able to degrade naphthalene nor reduce sulfate or other sulfur compounds in pure culture [ 15 ]. Other possible species might exist in this enrichment with unknown functions, but were not detected by terminal restriction fragment length polymorphism fingerprinting [ 15 ] because they represented less than 1% of the total DNA [ 16 ].…”

Rectinema subterraneum sp. nov, a chemotrophic spirochaete isolated from the deep terrestrial subsurface

“…It was most closely related to the cultured isolate Rectinema cohabitans (99% nucleotide identity). Despite high 16S rRNA nucleotide identity, we propose SURF-ANA1 T represents a novel species due to the numerous physiological and morphological characteristics that distinguish it from Rectinema cohabitans strain HM T [10]. These defining characteristics include: (1) Fundamental, characteristic helical morphology and presence of motility via polar flagella [24,25] in strain SURF-ANA1 T (Figs 1a, b and 2c) versus rod-shaped morphology and absence of flagella in R. cohabitans strain HM T .…”

“…(3) SURF-ANA1 T can utilize more versatile substrates for its energy metabolism compared to R. cohabitans (Table 2). (4) Although the fluids from which SURF-ANA1 T were collected have abundant putative sulfate-reducing Deltaproteobacteria [11,26,27], members of this lineage did not appear to be a necessary cohabitant as they do for R. cohabitans [10,28]. The next closest cultured isolates, isolates that demonstrate more similar morphology, are Treponema stenostrepta (88% nucleotide identity) and Treponema caldaria (87% nucleotide identity).…”

“…Based on the physiological distinctness and taxonomic characterization we propose that strain SURF-ANA1 T is a new species within the family Spirochaetaceae. Although members of the family Spirochaetaceae have been implicated in human disease or are possibly parasitic or symbiotic in termite or other animal guts [6][7][8], the widespread identification of spirochaete 16S rRNA gene sequences in global anoxic environments [1,2,4,9,10] would indicate that they also play an ecological role in more pristine environments as well. In the anoxic subsurface fluids at SURF, members of SURF-ANA1 T are likely not primary producers as other chemolithoautotrophs in the community could be.…”