Anoxygenic, photosynthetic bacteria are common at redox boundaries. They are of interest in microbial ecology and geosciences through their role in linking the carbon, sulfur, and iron cycles, yet much remains unknown about how their flexible carbon metabolism—permitting either autotrophic or heterotrophic growth—is recorded in the bulk sedimentary and lipid biomarker records. Here, we investigated patterns of carbon isotope fractionation in a model photosynthetic sulfur‐oxidizing bacterium, Allochromatium vinosum DSM180^T. In one treatment, A. vinosum was grown with CO₂ as the sole carbon source, while in a second treatment, it was grown on acetate. Different intracellular isotope patterns were observed for fatty acids, phytol, individual amino acids, intact proteins, and total RNA between the two experiments. Photoautotrophic CO₂ fixation yielded typical isotopic ordering for the lipid biomarkers: δ¹³C values of phytol > n‐alkyl lipids. In contrast, growth on acetate greatly suppressed intracellular isotopic heterogeneity across all molecular classes, except for a marked ¹³C‐depletion in phytol. This caused isotopic “inversion” in the lipids (δ¹³C values of phytol < n‐alkyl lipids). The finding suggests that inverse δ¹³C patterns of n‐alkanes and pristane/phytane in the geologic record may be at least in part a signal for photoheterotrophy. In both experimental scenarios, the relative isotope distributions could be predicted from an isotope flux‐balance model, demonstrating that microbial carbon metabolisms can be interrogated by combining compound‐specific stable isotope analysis with metabolic modeling. Isotopic differences among molecular classes may be a means of fingerprinting microbial carbon metabolism, both in the modern environment and the geologic record.

中文翻译：

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地球化学上不同的碳同位素分布在光养和光养养的异色变色DSM 180T中。

产氧的光合细菌在氧化还原边界很常见。他们通过在碳，硫和铁循环之间的联系而对微生物生态学和地球科学感兴趣，但对于如何在大量沉积物和脂质生物标志物中记录其灵活的碳代谢（允许自养或异养生长）仍知之甚少记录。在这里，我们研究了模式光合硫氧化细菌异色变菌DSM180 ^T中碳同位素分馏的模式。在一种处理中，葡萄菌与CO ₂一起生长作为唯一的碳源，在第二次处理中，它是在醋酸盐上生长的。在两次实验之间，观察到脂肪酸，植醇，单个氨基酸，完整蛋白和总RNA的不同细胞内同位素模式。光自养CO ₂固定为得到脂质生物标记典型同位素排序：δ ¹³植醇的C值>  ñ -烷基脂质。相反，在乙酸盐上的生长在所有分子类别上都大大抑制了细胞内同位素异质性，但植醇中的¹³ C损耗明显。这引起了同位素“反转”的脂质（δ ^13个植醇<的C值 ñ -烷基脂质）。这一发现表明，逆δ ¹³的Ç图案正烷烃和的地质记录姥鲛烷/植可以至少部分地用于photoheterotrophy的信号。在这两个实验方案中，都可以通过同位素通量平衡模型预测相对同位素分布，这表明可以通过将化合物特定的稳定同位素分析与代谢建模相结合来询问微生物碳代谢。在现代环境和地质记录中，分子类别之间的同位素差异可能是指纹识别微生物碳代谢的一种方式。