Fatty Acids of Chthonomonas calidirosea, of a Novel Class Chthonomonadetes from a Recently Described Phylum Armatimonadetes

Abstract

A Gram-negative, aerobic, pink-pigmented, rod-shaped bacterium Chthonomonas calidirosea (strain T49^T) with an optimal temperature for growth of 68 °C, isolated from soil samples from Hell’s Gate in the Tikitere geothermal system (New Zealand), was the first cultivated bacterium of the novel phylum Armatimonadetes (formerly candidate division OP10). The lipid composition of C. calidirosea presents a number of unusual features both in the fatty acids and polar lipids. This contribution reports on the fatty acid profile of C. calidirosea. Transmethylation of bacterial biomass yielded fatty acid methyl esters and hydrocarbons, including squalene, partially hydrogenated squalenes, and diploptene. The only type of unsaturation found in C. calidirosea fatty acids was cis-Δ5, as revealed by GCMS of dimethyl disulfide (DMDS) adducts, and the lack of trans-unsaturation absorbance at 960–980 cm⁻¹ in the IR spectrum of fatty acids methyl esters. An unidentified component X with ECL 16.86 (BP1) and ECL 17.27 (BP20) was also observed, with molecular ion at m/z 282 (“17:1”). X did not form DMDS adducts, nor was affected by mild hydrogenation conditions, indicating the likely presence of a ring rather than unsaturation. The presence of a cyclopropane ring with cis-stereochemistry was confirmed by the ¹H-NMR spectrum. Hydrogenation of X in acetic acid resulted in formation of straight chain 17:0, 5-methyl- and 6-methyl-16:0 fatty acid methyl esters, thus confirming the structure of a novel 5,6-methylene hexadecanoic acid. The major fatty acids of a solid media-grown C. calidirosea were as follows (in weight % of total fatty acids): 16:0 (25.8), i17:0 (19.3), ai17:0 (13.5), 16:1∆5 (8.8), i17:1∆5 (6.8), 5,6-methylene 16:0 (5.2), i16:0 (4.4), 18:0 (3.6), 18:1∆5 (3.2).