Signature Lipids and Stable Carbon Isotope Analyses of Octopus Spring Hyperthermophilic Communities Compared with Those of Aquificales Representatives

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Abstract
The molecular and isotopic compositions of lipid biomarkers of cultured Aquificales genera have been used to study the community and trophic structure of the hyperthermophilic pink streamers and vent biofilm from Octopus Spring. Thermocrinis ruber, Thermocrinis sp. strain HI 11/12,Hydrogenobacterthermophilus TK-6,Aquifex pyrophilus, and Aquifex aeolicusall contained glycerol-ether phospholipids as well as acyl glycerides. The n-C20:1 andcy-C21 fatty acids dominated all of theAquificales, while the alkyl glycerol ethers were mainly C18:0. These Aquificales biomarkers were major constituents of the lipid extracts of two Octopus Spring samples, a biofilm associated with the siliceous vent walls, and the well-known pink streamer community (PSC). Both the biofilm and the PSC contained mono- and dialkyl glycerol ethers in which C18 and C20 alkyl groups were prevalent. Phospholipid fatty acids included both the Aquificales n-C20:1 andcy-C21, plus a series ofiso-branched fatty acids (i-C15:0 toi-C21:0), indicating an additional bacterial component. Biomass and lipids from the PSC were depleted in13C relative to source water CO2 by 10.9 and 17.2‰, respectively. The C20–21 fatty acids of the PSC were less depleted than the iso-branched fatty acids, 18.4 and 22.6‰, respectively. The biomass of T. rubergrown on CO2 was depleted in 13C by only 3.3‰ relative to C source. In contrast, biomass was depleted by 19.7‰ when formate was the C source. Independent of carbon source, T. ruber lipids were heavier than biomass (+1.3‰). The depletion in the C20–21 fatty acids from the PSC indicates thatThermocrinis biomass must be similarly depleted and too light to be explained by growth on CO2. Accordingly,Thermocrinis in the PSC is likely to have utilized formate, presumably generated in the spring source region.