Summary:
Green, nonsulfur-like bacteria (GNSLB) and cyanobacteria form major components of microbial mats in both sulfidic and non-sulfidic hot springs and have been mainly studied in hot springs of Yellowstone National Park (YNP). These organisms synthesize specific lipid biomarkers such as wax esters and long chain polyunsaturated alkenes (GNSLB) and heptadecane (cyanobacteria). We analyzed the lipid distribution and their stable carbon isotopic composition in sulfidic Icelandic hot spring microbial mats known to contain GNSLB and cyanobacteria. Based on the lipid distribution, it seems that the GNSLB in these mats are closely related to Chloroflexus aurantiacus. The stable carbon isotopic composition of the bulk biomass and wax esters suggests mainly autotrophic growth by GNSLB in this sulfidic hot spring. However, the stable carbon isotopic composition of hentriacontatriene in the two GNSLB mats suggests an alternative carbon source for the C31:3 alkene producing GNSLB from that in YNP. The isotopic composition of cyanobacterial biomarkers in the mat most distant from the source of the hot spring seems to suggest inorganic carbon limitation for cyanobacteria, possibly because they grow underneath the GNSLB in these sulfidic hot spring inverted microbial mats.