Chthonomonas calidirosea gen. nov., sp. nov., an aerobic, pigmented, thermophilic micro-organism of a novel bacterial class, Chthonomonadetes classis nov., of the newly described phylum Armatimonadetes originally designated candidate division OP10

Abstract

An aerobic, saccharolytic, obligately thermophilic, motile, non-spore-forming bacterium, strain T49T, was isolated from geothermally heated soil at Hell’s Gate, Tikitere, New Zealand. On the basis of 16S rRNA gene sequence similarity, T49T is the first representative of a new class in the newly described phylum Armatimonadetes, formerly known as candidate division OP10. Cells of strain T49T stained Gram-negative and were catalase-positive and oxidase-negative. Cells possessed a highly corrugated outer membrane. The major fatty acids were 16 : 0, i17 : 0 and ai17 : 0. The G+C content of the genomic DNA was 54.6 mol%. Strain T49T grew at 50–73 °C with an optimum temperature of 68 °C, and at pH 4.7–5.8 with an optimum growth pH of 5.3. A growth rate of 0.012 h−1 was observed under optimal temperature and pH conditions. The primary respiratory quinone was MK-8. Optimal growth was achieved in the absence of NaCl, although growth was observed at NaCl concentrations as high as 2 % (w/v). Strain T49T was able to utilize mono- and disaccharides such as cellobiose, lactose, mannose and glucose, as well as branched or amorphous polysaccharides such as starch, CM-cellulose, xylan and glycogen, but not highly linear polysaccharides such as crystalline cellulose or cotton. On the basis of its phylogenetic position and phenotypic characteristics, we propose that strain T49T represents a novel bacterial genus and species within the new class Chthonomonadetes classis nov. of the phylum Armatimonadetes. The type strain of Chthonomonas calidirosea gen. nov., sp. nov. is T49T ( = DSM 23976T = ICMP 18418T).

Genomic analysis of Chthonomonas calidirosea, the first sequenced isolate of the phylum Armatimonadetes

“…Succinyl CoA is generated via isocitrate dehydrogenase and 2-oxoglutarate dehydrogenase complex. T49 T has previously been reported as exhibiting obligate chemoheterotrophic metabolism (Lee et al, 2011). In addition to these previous cultivation experiments, we predicted and experimentally confirmed its ability to utilise several less-common carbohydrates and associated derivatives, including sorbitol and galactan.…”

“…The placement of T49 T within the phylum Armatimonadetes was previously investigated through 16S rRNA-based analysis (Lee et al, 2011). However, the 16S rRNA gene alone does not reliably resolve the relationships among deeply branching phyla (Delsuc et al, 2005).…”

“…Although phosphoenolpyruvate carboxylase is a critical enzyme for the first step of carbon fixation in C4 and crassulacean acid metabolism plants (O' Leary and Diaz, 1982), the role of phosphoenolpyruvate carboxylase here appears to be limited to an anaplerotic role in maintaining the balance of intermediary molecules within the tricarboxylic acid cycle (Dunn, 2011); this is logical as the fixation of carbon dioxide is energetically unfavourable compared with the organic carbon substrates from which C. calidirosea T49 T is capable of deriving energy. Nitrogen uptake by T49 T was experimentally determined to be via ammonia assimilation and/or amino acid uptake (Lee et al, 2011). It appears that ammonia can be assimilated via glutamate or glycine and modified by a complete tetrahydrofolate onecarbon pathway.…”

“…The first reported cultivated strains of candidate division OP10, strains T49 T and P488, were isolated from geothermally heated soils in New Zealand (Stott et al, 2008). To date, three species from the Armatimonadetes have been formally described: C. calidirosea T49 T (Lee et al, 2011), Fimbriimonas ginsengisoli GSoil348 T and the phylum type species, Armatimonas rosea YO-36 T (Tamaki et al, 2011). These strains are only distantly related, with 16S rRNA gene sequence similarities of o80% (Dunfield et al, 2012).…”

“…However, in contrast to the mesophilic and neutrophilic A. rosea and F. ginsengisoli, T49 T is a thermophile (T opt 68 1C, range: 50-73 1C) and a moderate acidophile (growth pH 5.3, range: pH 4.7-5.8). The three strains differ in mol% G þ C content, cell morphology, fatty acid content, quinone and salt tolerance (Lee et al, 2011, Tamaki et al, 2011). In addition, T49 T appears to have a much broader carbohydrate utilisation range, including a partially cellulolytic phenotype; it can hydrolyse amorphous polysaccharides but not linear polysaccharides (Lee et al, 2011).…”