Australia: The Land Where Time Began

A biography of the Australian continent 

The Great Oxidation Event - Evolution of Multicellularity Coincided with an Increase of Cyanobacterial Diversification

Cyanobacteria have morphotypes that range from unicellular to filamentous forms that are multicellular, some of which are capable of differentiating terminally (irreversibly) in form and function. According to the authors¹ it has been suggested that the concentrations of oxygen in the atmosphere were increased by cyanobacteria about 2.45-2.32 Ga at the time of the Great Oxidation Event (GOE), which resulted in a dramatic change in life on Earth. The temporal evolution of the lineages of cyanobacteria, and possible any interplay between the origin of multicellularity, cyanobacterial diversification, and the rise of oxygen in the atmosphere. The divergence of extant cyanobacterial lineages were estimated by the authors¹ under Bayesian relaxed clocks for 16S rRNA sequences dataset that represented the entire known diversity of the phylum, to test if the evolution of multicellularity overlapped with the GOE, and whether there is an association between multicellularity and significant diversification rate shifts in cyanobacteria. It is indicated by their results that cyanobacteria arose before the atmospheric oxygen levels increased, the evolution of forms that were multicellular coinciding with the onset of the GOE and an increase in the rate of diversification. Multicellularity is suggested by these results to have had a key role in the triggering of cyanobacterial evolution around the time of the GOE.

The Great Oxidation Event - More Oxygen Through Multicellularity² 

According to a team of scientists from the University of Zurich multicellularity was developed by cyanobacteria about 1 billion years before the eukaryotes, following which the process of molecular oxygen release began in the oceans and oxygen was eventually released to the atmosphere as the rate of oxygen production in the ocean increased enough to exceed the rate at which oxygen was being used in the ocean for oxidation. When the results obtained by Bettina Schirrmeister and her team carried out analysis of the phylogeny of extant cyanobacteria, which were combined with data from the fossil record of cyanobacteria, it suggested that multicellular cyanobacteria had emerged much earlier than had previously been believed, at some time earlier than 2.3 Ga.

The researchers suggest multicellularity was achieved by cyanobacteria shortly before the rise of free oxygen in the oceans and eventually in the atmosphere, which occurred in the Great Oxidation Event, that is often referred to as the most significant climatic event in the history of the Earth. Schirrmeister et al. have suggested, based on their data, that there is a link between the GOE and the emergence of multicellularity. Homayoun Bagheri, Schirrmeister's supervisor, suggests the metabolism of multicellular forms is often more efficient than that of unicellular forms. Therefore the researchers propose that it was the development of multicellularity of the cyanobacteria that played a key role in the GOE.

The increasing amounts of molecular oxygen in the oceans and the atmosphere made big changes to the original atmosphere, and this would have impacted heavily on anaerobic organisms as the free oxygen was poisonous to them, and this would have eliminated many forms of anaerobic bacteria, so opening their vacated ecological niches for the cyanobacteria to expand into. It was found by Schirrmeister and her team that following the change in the oceans and the atmosphere there were many new types of multicellular cyanobacteria, they deduced that these new cyanobacteria occupied the many newly available habitats.

Sources & Further reading

1. Schirrmeister, Bettina E., Jurriaan M. de Vos, Alexandre Antonelli, and Homayoun C. Bagheri. "Evolution of Multicellularity Coincided with Increased Diversification of Cyanobacteria and the Great Oxidation Event." Proceedings of the National Academy of Sciences 110, no. 5 (January 29, 2013 2013): 1791-96.
2. 17 January 2013,"The Great Oxidation Event - More Oxygen Through Multicellularity", Science News, ScienceDaily.