δ13C–δD distribution of lipid biomarkers in a bacterial mat from a hot spring in Miyagi Prefecture, NE Japan

Bacterial communities often develop with distinct metabolisms in hot springs using various chemical substrates. The carbon and hydrogen isotopic compositions of characteristic lipid biomarkers such as C16:1 and C20:1 fatty acids (FAs) have been determined in a bacterial mat at the Naruko hot spring, Japan. The C20:1 FA is extremely enriched in 13C (−0.5‰) and derives from hydrogen-oxidizing bacteria which fix carbon via the reversed tricarboxylic acid cycle. On the other hand, the C16:1 FA has a δ13C value of −36.8‰, consistent with an origin in sulfur-oxidizing bacteria utilizing the Calvin cycle for carbon fixation. The C20:1 FA is more depleted in D (−469‰) by ca. 300‰ than the C16:1 FA (−173‰), suggesting a D-depleted hydrogen pool (NADH or NADPH) for lipid synthesis by the hydrogen-oxidizing bacteria. The distinct δ13C–δD distribution of lipid biomarkers is useful for clarifying the metabolic pathways between different organisms in a bacterial ecosystem in hot springs.