Fossilized carotenoid hydrocarbons provide a window into the physiology and biochemistry of ancient microbial phototrophic communities for which only a sparse and incomplete fossil record exists. However, accurate interpretation of carotenoid-derived biomarkers requires detailed knowledge of the carotenoid inventories of contemporary phototrophs and their physiologies. Here we report two distinct patterns of fossilized C₄₀ diaromatic carotenoids. Phanerozoic marine settings show distributions of diaromatic hydrocarbons dominated by isorenieratane, a biomarker derived from low-light-adapted phototrophic green sulfur bacteria. In contrast, isorenieratane is only a minor constituent within Neoproterozoic marine sediments and Phanerozoic lacustrine paleoenvironments, for which the major compounds detected are renierapurpurane and renieratane, together with some novel C₃₉ and C₃₈ carotenoid degradation products. This latter pattern can be traced to cyanobacteria as shown by analyses of cultured taxa and laboratory simulations of sedimentary diagenesis. The cyanobacterial carotenoid synechoxanthin, and its immediate biosynthetic precursors, contain thermally labile, aromatic carboxylic-acid functional groups, which upon hydrogenation and mild heating yield mixtures of products that closely resemble those found in the Proterozoic fossil record. The Neoproterozoic–Phanerozoic transition in fossil carotenoid patterns likely reflects a step change in the surface sulfur inventory that afforded opportunities for the expansion of phototropic sulfur bacteria in marine ecosystems. Furthermore, this expansion might have also coincided with a major change in physiology. One possibility is that the green sulfur bacteria developed the capacity to oxidize sulfide fully to sulfate, an innovation which would have significantly increased their capacity for photosynthetic carbon fixation.

化石化的类胡萝卜素碳氢化合物为古代微生物光养群落的生理学和生物化学提供了一个窗口，对于这些微生物，仅存在稀疏和不完整的化石记录。但是，要准确解释类胡萝卜素衍生的生物标记，需要对当代照相营养类胡萝卜素清单及其生理学有详细的了解。在这里我们报告了两种不同的化石C ₄₀模式芳族类胡萝卜素。准生代海洋环境显示了以异戊烯烷为主要成分的二芳烃的分布，异戊烯烷是一种来自弱光适应性光养绿硫细菌的生物标记。相比之下，异戊二烯仅是新元古代海洋沉积物和生代湖泊湖古环境中的次要成分，检出的主要化合物为肾上紫嘌呤和肾上腺素，以及一些新颖的C ₃₉和C ₃₈类胡萝卜素降解产物。后一种模式可以追溯到蓝细菌，如培养的分类单元的分析和沉积成岩作用的实验室模拟所示。蓝藻类胡萝卜素突触花青素及其直接的生物合成前体含有热不稳定的芳族羧酸官能团，在氢化和温和加热下，它们的产物混合物与元古代化石记录中的产物极为相似。化石类胡萝卜素模式的新元古代-杂元古代过渡可能反映了表面硫库存的逐步变化，这为海洋生态系统中的向光性硫细菌的扩展提供了机会。此外，这种扩展可能还与生理学的重大变化相吻合。