The carbon isotope composition of lipids has been widely used to decode the biogeochemical cycle and reconstruct paleo-environment and paleo-ecological changes over geologic time. However, up to now, little is known about the controls on the carbon isotope signatures of heterotrophic microbes with ecological functions in the ocean. Here, we investigate the carbon isotope fractionation between fatty acids and carbon sources by a representative marine bacterium Shewanella piezotolerans WP3 growing on different organic substrates, including N-acetyl-D-glucosamine (GlcNac), glucose, acetate, pyruvate, L-alanine, and L-glutamate. The effect of growth temperature on the carbon isotope fractionation is also examined using GlcNac as sole carbon source. Our results show that the carbon isotope fractionations vary obviously between different carbon sources: fatty acids are strongly depleted in ¹³C growing on GlcNac and glucose with abundance-weighted average ¹³C/¹²C fractionations ranging from −7.7 to −3.8‰, slightly depleted in ¹³C on acetate and L-alanine (−0.8 to −0.4‰), and enriched in ¹³C on pyruvate and L-glutamate (0.6–2.1‰). More importantly, we found a considerable variation of fractionations between different growth temperatures with strongly ¹³C-depleted at optimal growth temperature (15–20 °C) with abundance-weighted average ¹³C/¹²C fractionations ranging from −5.2 to −4.8‰ and relatively small fractionations on 4 °C, 10 °C and 25 °C (−2.1 to −3.4‰). We hypothesize that the controls on carbon isotope fractionation are associated with decarboxylation and oxidation-related dehydrogenase complex under different growth temperatures. This study proves that carbon isotope fractionation in heterotrophs is related to which pathway for carbon sources enter into the central metabolism, and may be served as useful “fingerprints” for interpreting carbon isotope signatures in sedimentary lipids, and inferring ecological functions of S. piezotolerans WP3 in certain environments, especially in Fe-reducing oceanic sediments.

脂质的碳同位素组成已被广泛用于解码生物地球化学循环并重建古环境和古生态随地质时间的变化。然而，到目前为止，对海洋中具有生态功能的异养微生物碳同位素特征的控制知之甚少。在这里，我们研究了在不同有机基质（包括N-乙酰基-D-氨基葡萄糖 (GlcNac)、葡萄糖、乙酸盐、丙酮酸盐、L-丙氨酸和 L-谷氨酸盐。还使用 GlcNac 作为唯一碳源检查了生长温度对碳同位素分馏的影响。^{我们的研究结果表明，不同碳源之间的碳同位素分馏明显不同：在 GlcNac 和葡萄糖上生长的13} C中脂肪酸强烈消耗，丰度加权平均¹³ C/ ¹² C 分馏范围为 -7.7 至 -3.8‰，略有消耗在¹³ C 的乙酸盐和 L-丙氨酸（-0.8 至 -0.4‰）上，富含¹³C 对丙酮酸和 L-谷氨酸 (0.6–2.1‰)。更重要的是，我们发现不同生长温度之间的分馏存在相当大的差异，在最佳生长温度（15-20°C）下强烈耗尽^{13 C，丰度加权平均值为13} C/ ¹²C 分馏范围为 -5.2 至 -4.8‰，在 4 °C、10 °C 和 25 °C（-2.1 至 -3.4‰）时分馏相对较小。我们假设对碳同位素分馏的控制与不同生长温度下的脱羧和氧化相关脱氢酶复合物有关。本研究证明异养生物中的碳同位素分馏与碳源进入中央代谢的途径有关，可作为解释沉积脂质中碳同位素特征和推断S. piezotolerans WP3生态功能的有用“指纹”在某些环境中，特别是在减少铁的海洋沉积物中。