Details

Autor(en) / Beteiligte

• Cui, Xingqian
• Liu, Xiao-Lei
• Shen, Gaozhong
• Ma, Jian
• Husain, Fatima
• Rocher, Donald
• Zumberge, John E.
• Bryant, Donald A.
• Summons, Roger E.

Titel

Niche expansion for phototrophic sulfur bacteria at the Proterozoic–Phanerozoic transition

Ist Teil von

• Proceedings of the National Academy of Sciences - PNAS, 2020-07, Vol.117 (30), p.17599-17606

Ort / Verlag

Washington: National Academy of Sciences

Erscheinungsjahr

2020

Link zum Volltext

Quelle

Electronic Journals Library

Beschreibungen/Notizen

• 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 expansionmight 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.