Cyanobacterial evolution during the Precambrian

Abstract

Life on Earth has existed for at least 3.5 billion years. Yet, relatively little is known of its evolution during the first two billion years, due to the scarceness and generally poor preservation of fossilized biological material. Cyanobacteria, formerly known as blue green algae were among the first crown Eubacteria to evolve and for more than 2.5 billion years they have strongly influenced Earth's biosphere. Being the only organism where oxygenic photosynthesis has originated, they have oxygenated Earth's atmosphere and hydrosphere, triggered the evolution of plants -being ancestral to chloroplasts-and enabled the evolution of complex life based on aerobic respiration. Having such a strong impact on early life, one might expect that the evolutionary success of this group may also have triggered further biosphere changes during early Earth history. However, very little is known about the early evolution of this phylum and ongoing debates about cyanobacterial fossils, biomarkers and molecular clock analyses highlight the difficulties in this field of research. Although phylogenomic analyses have provided promising glimpses into the early evolution of cyanobacteria, estimated divergence ages are often very uncertain, because of vague and insufficient tree-calibrations. Results of molecular clock analyses are intrinsically tied to these prior calibration points, hence improving calibrations will enable more precise divergence time estimations. Here we provide a review of previously described Precambrian microfossils, biomarkers and geochemical markers that inform upon the early evolution of cyanobacteria. Future research in micropalaeontology will require novel analyses and imaging techniques to improve taxonomic affiliation of many Precambrian microfossils. Consequently, a better understanding of early cyanobacterial evolution will not only allow for a more specific calibration of cyanobacterial and eubacterial phylogenies, but also provide new dates for the tree of life.

Biosilicification Drives a Decline of Dissolved Si in the Oceans through Geologic Time

“…The main problems with molecular clocks include differences in fossil-based calibration points, differences in molecular clock rate models, differences in amino acid substitution rates among various parts of the dataset and uncertainty in the phylogenetic tree, thus limiting the precision that can be achieved in estimates of ancient molecular timescales (dos Reis et al, 2015). Cyanobacteria are at least 2.3-3 Ga old from molecular clock studies (Dvorák et al, 2014;Sanchez-Baracaldo, 2015), whereas fossil evidence (stromatolites, microfossils, carbon isotopes, biomarkers, signs of oxygen) from Greenland, Australia and elsewhere have raised the possibility of cyanobacteria older than 3 Gy, although these claims are disputed (Schirrmeister et al, 2016).…”

On the origin of oxygenic photosynthesis and Cyanobacteria

“…Regarding the timing of origin, the fossil record of Cyanobacteria is not conclusive (Schirrmeister et al, 2016). A fundamental question in biology is when oxygenic photosynthesis first evolved.…”

“…1) (Hug et al, 2016;Ward et al, 2019). At the organismal level, phylogenomic approaches unravel the evolutionary history of organisms that are currently able to perform oxygenic photosynthesis (Blank & S anchez-Baracaldo, 2010;Schirrmeister et al, 2013Schirrmeister et al, , 2016. While, to an extent, it is reasonable to interchange both terms, there are significant differences when referring to oxygenic photosynthesis and Cyanobacteria.…”

A Metagenomic Approach to Cyanobacterial Genomics

“…Most research on cyanobacteria is guided by evolutionary, ecological, ecotoxicological, biochemical, and taxonomic concerns (for a review on common investigation topics regarding cyanobacteria see Sciuto and Moro, 2015). Cyanobacteria were amongst the earliest organisms on the planet and synthesized important molecules for primitive life (Banack et al, 2012; Schirrmeister et al, 2016). Later, microorganisms of this phylum were responsible for oxygenating Earth's atmosphere (Shih et al, 2017) and originating chloroplasts (Alda et al, 2014).…”