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.
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