Compound-specific isotopic fractionation patterns suggest different carbon metab lisms among Chloroflexus-like bacteria in hot-spring microbial mats

Stable carbon isotope fractionations between dissolved inorganic carbon and lipid biomarkers suggest photoautotrophy by Chloroflexus-like organisms in sulfidic and nonsulfidic Yellowstone hot springs. Where co-occurring, cyanobacteria appear to cross-feed Chloroflexus-like organisms supporting photoheterotrophy as well, although the relatively small C-13 fractionation associated with cyanobacterial sugar biosynthesis may sometimes obscure this process.