MICROBIAL COMMUNITY BIOSIGNATURES IN SILICA-DEPOSITING, THERMAL HOT SPRINGS: GRAND PRISMATIC SPRING, YELLOWSTONE NATIONAL PARK

The microbial communities that characterize modern hydrothermal ecosystems serve as modern analogs to those thought to have dominated early environments on Earth and possibly Mars. Our goal is to establish community biosignatures and to understand their potential preservation within silica-rich microbial ecosystems. Here we are interested in the microbial communities associated with a thermal gradient supported by the outflow of Grand Prismatic Spring, Yellowstone National Park. Transects were established from the high temperature spring source to the cooler distal apron through both Phormidium and Calothrix zones. Near the source, a green streamer community composed of Cyanothece entwined in fine bacterial filaments grew over a pinkish underlying sinter approximately 1-cm in depth. The membrane lipids representative of the microbes in both the green streamers (GS) and pinkish sinter mat (PSM) were composed of distinct types of ester-linked fatty acids (FA) indicating the presence of novel bacterial groups. A relatively large proportion of both glycolipids and phospholipids, particularly in GS, was comprised of three branched FA classes. 1) The iso-anteiso FA normally associated with gram-positive bacteria but also some Chloroflexi. 2) A series of mid-chain branched FA (possibly 10-methyls) from C₁₇ to C₂₁, primarily C₁₉, and 3) a series of novel 2-methyl FA from C₁₈ to C₂₂. These 2-methyl fatty acids were isolated primarily from the phospholipids of both GS and PSM samples, and in the underlying sinter were accompanied by a series of 2,X-dimethyl fatty acids. Wax esters, a biomarker for Chloroflexi, were present in large amounts in the PSM with a FA to WXE ratio of 2:1, and were composed of a normal, normal-series (C_32-36), composed of at least one C₁₇ moiety and primarily (45%) C₁₇-C₁₇. Cyanobacterial alkanes in the GS were represented by two apparent classes: 1) a series represented by n-17, monomethyl-17 (7-, 6- and 5-methyls), and dimethyl-17 (7,11-dimethyl), and 2) n-19 and two isomers of n-19:1. Also present in the GS was another Chloroflexi biomarker, long-chain di- and trienes (C_29-31), primarily C_31:3 >C_29:2> C_31:2. These long-chain alkenes were present at much lower concentrations in the PSM, and together with lower WXE in the GS, indicate different Chloroflexi in GS and PSM communities.