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

Abstract

<jats:p>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 C<jats:sub>40</jats:sub> 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 C<jats:sub>39</jats:sub> and C<jats:sub>38</jats:sub> 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.</jats:p>

Redox-Controlled Ammonium Storage and Overturn in Ediacaran Oceans

“…In broad terms, this is in agreement with a strikingly large variation of bacterial hopanes over eukaryotic steranes observed throughout the Ediacaran (Brocks et al, 2017;Pehr et al, 2018;van Maldegem et al, 2019), which led to the suggestion that on regional scales primary productivity was likely modulated by local determinants such as nutrient supply (Pehr et al, 2018). It is also consistent with distributions of carotenoid pigments (Cui et al, 2020).…”

Biomarker stratigraphy in the Athel Trough of the South Oman Salt Basin at the Ediacaran‐Cambrian Boundary

“…strain PCC 7002 and relates species, which synthesize renierapurpurin (XIX) as an intermediate in the biosynthesis of the cyanobacterial carotenoid χ,χ‐caroten‐18,18’‐dioic acid (XXV), otherwise known as synechoxanthin, via the intermediates XXI, XXII, and XXIV (Graham & Bryant, 2008; Graham, Lecomte, & Bryant, 2008). Further research has confirmed production of renieratene and traces of isorenieratene from these strains (Cui et al., 2020). Studies of the presence of synechoxanthin in Synechococcus sp.…”

“…French et al (2020) Graham, Lecomte, & Bryant, 2008). Further research has confirmed production of renieratene and traces of isorenieratene from these strains (Cui et al, 2020). Studies of the presence of synechoxanthin in Synechococcus sp.…”

Molecular and isotopic evidence reveals the end-Triassic carbon isotope excursion is not from massive exogenous light carbon

“…2). Renieratane and renierapurpurane are carotenoid biomarkers sourced from numerous strains of cyanobacteria (31,32) and high (ren+rnp)/iso ratios, as observed in the upper CIE, are typical of Phanerozoic lacustrine settings with low sulfate inventories (33). Increases in chlorobactane and okenane carotenoid biomarkers suggest expansion of anoxic green-pigmented GSB and PSB layers in microbial mats beneath surficial cyanobacterial layer(s) (Fig.…”