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 Aqu ificales genera have been used to study the community and trophic structure of the hyperthermophilic pink streamers and vent biofilm from Octopus Spri ng. Thermocrinis ruber, Thermocrinis sp. strain HI 11/12, Hydrogenobacter t hermophilas TK-6, Aquifex pyrophilus, and Aquifex aeolicus all contained gl ycerol-ether phospholipids as well as acyl glycerides. The n-C-20:1 and cy- C-21 fatty acids dominated all of the Aquificales, while the alkyl glycerol ethers were mainly C-18:0, These Aquificales biomarkers were major constit uents of the lipid extracts of two Octopus Spring samples, a biofilm associ ated with the siliceous vent walls, and the well-known pink streamer commun ity (PSC). Both the biofilm and the PSC contained mono- and dialkyl glycero l ethers in which C-18 and C-20 alkyl groups were prevalent. Phospholipid f atty acids included both the Aquificales n-C-20:1 and cy-C-21, plus a serie s of isobranched fatty acids (i-C-15:0 to i-C-21:0), indicating an addition al bacterial component. Biomass and lipids from the PSC were depleted in C- 13 relative to source water CO2 by 10.9 and 17.2 parts per thousand, respec tively. The C20-21 fatty acids of the PSC were less depleted than the iso-b ranched fatty acids, 18.4 and 22.6 parts per thousand, respectively. The bi omass of T. ruber grown on CO2 was depleted in C-13 by only 3.3 parts per t housand relative to C source. In contrast, biomass was depleted by 19.7 par ts per thousand when formate was the C source. Independent of carbon source , T. ruber lipids were heavier than biomass (+1.3 parts per thousand). The depletion in the C20-21 fatty acids from the PSC indicates that Thermocrini s biomass must be similarly depleted and too light to be explained by growt h on CO2. Accordingly, Thermocrinis in the PSC is likely to have utilized f ormate, presumably generated in the spring source region.