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

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. Thermocrinix ruher, Thermocrinis sp. strain III 11/12, Hydrogenobacter thermophilus TK-6, Aquifexpyrophiltts, and Aquifex aeolicus all contained glycerol-ether phospholipids as well as acyl glycerides. The n-C_20:1 and cy-C₂₁ fatty acids dominated all of the Aquificales, while the alkyl glycerol ethers were mainly C_18:0. 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-C_20:1 and cy-C₂₁, plus a series of isobranched fatty acids (i-C_15:0 to i-C_21:0), indicating an additional bacterial component. Biomassand lipids from the PSC were depleted in CO₂ relative to source water CO₂ by 10.9 and 17.2%, respectively. The C_20-21 fatty acids of the PSC were less depleted than the iso-branched fatty acids, 18.4 and 22.6%, respectively. The biomass of T. ruber grown on CO₂ was depleted in ¹³C by only 3.3%e relative to C source. In contrast, biomass was depleted by 19.7%_c when formate was the C source. Independent of carbon source, T. ruber lipids were heavier than biomass (+ 1.3%_c). The depletion in the C_20-21, fatty acids from the PSC indicates that Thermocrinis 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.