The evolutionary diversification of cyanobacteria: Molecular–phylogenetic and paleontological perspectives

Abstract

Cyanobacteria have played a significant role in Earth history as primary producers and the ultimate source of atmospheric oxygen. To date, however, how and when the group diversified has remained unclear. Here, we combine molecular phylogenetic and paleontological studies to elucidate the pattern and timing of early cyanobacterial diversification. 16S rRNA, rbcL, and hetR genes were sequenced from 20 cyanobacterial strains distributed among 16 genera, with particular care taken to represent the known diversity of filamentous taxa. Unlike most other bacteria, some filamentous cyanobacteria evolved a degree of cell differentiation, producing both specialized cells for nitrogen fixation (heterocysts) and resting cells able to endure environmental stress (akinetes). Phylogenetic analyses support the hypothesis that cyanobacteria capable of cell differentiation are monophyletic, and the geological record provides both upper and lower bounds on the origin of this clade. Fossil akinetes have been identified in 1,650-to 1,400-mega-annum (Ma) cherts from Siberia, China, and Australia, and what may be the earliest known akinetes are preserved in Ϸ2,100-Ma chert from West Africa. Geochemical evidence suggests that oxygen first reached levels that would compromise nitrogen fixation (and hence select for heterocyst differentiation) 2,450 -2,320 Ma. Integrating phylogenetic analyses and geological data, we suggest that the clade of cyanobacteria marked by cell differentiation diverged once between 2,450 and 2,100 Ma, providing an internal bacterial calibration point for studies of molecular evolution in early organisms. molecular evolution ͉ phylogeny ͉ Proterozoic

Hydrocarbon profiles and phylogenetic analyses of diversified cyanobacterial species

“…Phormidium lucidum FACHB 238 and Spirulina platensis FACHB 882 are filamentous strains belonging to the traditional subsection III taxa that lack the capability of heterocyst formation. In 16S rDNA trees, these two strains are placed with unicellular species, indicating polyphyletic origins of filamentous morphology within cyanobacteria, as previously reported [5]. When morphological examination and the analyses of the hydrocarbon profiles were combined with the phylogenetic analysis based on 16S rDNA sequences of 20 cyanobacterial strains, we found that strains with type 1 and type 2 hydrocarbon profiles were all filamentous, whereas the strains with type 4 and type 5 hydrocarbon profiles were all unicellular.…”

Antioxidant properties and polyphenolic content in terrestrial cyanobacteria

“…The detoxification of ROS by means of enzymatic and/or non-enzymatic antioxidants like phenylpropanoids protects cell damage and minimizes the loss due to oxidative responses (Reuter et al 2010). Since these organisms are among the most primitive prokaryotes having faced several extreme environmental stresses during their evolution (Tomitani et al 2006), it is imperative to understand that their capabilities to produce antioxidative enzymes and secondary metabolites might have offered them protective strategies against abiotic stresses.…”

Insights from genomic comparisons of genetically monomorphic bacterial pathogens

“…Evolutionary studies on microbes span the range of genetic diversity between the two microbial domains of life that evolved billions of years ago [1] down to genetic changes within a lineage that accumulate during the infection of a single diseased human over several weeks [2 -4]. Clearly, the predominant genetic mechanisms are likely to be distinct over the extremes of such an extensive range.…”