Multicellularity: A key event in the evolution of life

January 16, 2013, University of Bristol
Multicellularity: A key event in the evolution of life
Multicellular cyanobacteria with algae-like growth. Credit: Dr. Bettina Schirrmeister

(—Multicellularity in cyanobacteria originated before 2.4 billion years ago and is associated with the accumulation of atmospheric oxygen, subsequently enabling the evolution of aerobic life, as we know it today, according to a new study from the University of Zurich involving researchers now at the University of Bristol, and Gothenburg.

The research, published today in the (PNAS), applied phylogenetic tree reconstruction methods to the study of oxygen-producing bacteria, so-called cyanobacteria.

These bacteria show an impressive morphological variety, including multiple forms of multicellularity, and are distributed across various habitats, including oceans, lakes, soil and even . They are also amongst the oldest organisms on Earth and it seems that they are not only important for the ecosystem of our planet today but have been so for over two billion years.

It has been suggested that cyanobacteria raised in the atmosphere around 2.4 billion years ago during the Great Oxidation Event (GOE), when the anoxic and seemingly uninhabitable Earth started to slowly accumulate oxygen in its atmosphere, finally forming the planet that we see today, full of diverse habitats and species. Yet, little was known about the temporal of cyanobacterial , and the possible interplay between the origin of multicellularity, diversification of cyanobacteria and the rise of .

By combining information gathered from and the genes of , the researchers tested whether the evolution of multicellularity overlaps with the GOE, and whether multicellularity is associated with significant shifts in diversification rates in cyanobacteria.

They found that cyanobacteria originated long before the accumulation of oxygen in the atmosphere and that the evolution of multicellular forms coincided with the onset of the GOE and an increase in diversification rates. These results suggest that multicellularity could have played a key role in triggering cyanobacterial evolution around the GOE. The researchers also found that multicellularity was followed by increased origin of species in cyanobacteria.

Lead author, Dr Bettina Schirrmeister, Swiss National Science Foundation (SNF) postdoctoral fellow at the University of Bristol said: "Multicellularity originated very early in cyanobacteria and likely had a strong influence on the early environment of our planet. It could have had advantages that helped to dominate environmental niches, increasing the abundance of cyanobacteria and subsequently oxygen production."

"There is much discussion on the impact of environmental changes on biodiversity, for instance what will happen under current Global Warming. Our study stands out in showing a potential link in the other direction, namely how the evolution of biodiversity has profoundly changed the planet's environment", says Alexandre Antonelli, at the University of Gothenburg in Sweden.

The researchers' next aim is to get a better understanding of what might have caused the evolution of multicellularity in and its consequences.

Dr Schirrmeister said: "By applying state of the art techniques for the analyses of genomes and fossil data, we hope to get new clues on the dynamics that underlie the drastic environmental changes during the early Proterozoic Eon, more than two billion years ago."

Explore further: New bacterium forms intracellular minerals

More information: Schirrmeister, B. et al., Evolution of multicellularity coincided with increased diversification of cyanobacteria and the Great Oxidation Event, PNAS. … 927110.full.pdf+html

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not rated yet Jan 17, 2013
This is great! I have waited for a dating of cyanobacteria as it is crucial point and as the paper notes the unambigious molecular trace fossils appears first after GOE (earlier fossils are rejected lately). Also nice to see how bacterial multicellularity becomes acceptable.

The paper places the cyanobacteria originating on average ~ 3.0 Ga bp (billion years before present) _and_ their first diversification around that time. Since all cyanobacteria are aerobic (AFAIK) they would start to produce oxygen at that time, and indeed it overlaps with the first BIFs. http://www.galler.../bif.htm

This is now the oldest known bacteria. It is coincident with the Archaean Expansion of gene families. ["Rapid evolutionary innovation during an Archaean genetic expansion", David et al, Nature 2010] This is the period of diversification between Archaea and Bacteria. It is also the period of the late, late tail of impactors, which ends about the time of their multicellulars @ ~ 2.5 Ga bp.
not rated yet Jan 17, 2013
[ http://www.univer...ardment/ ]

Under such a scenario life would start very early, well before our current crust record at a guess, and impactors looks to be the external forcing that keeps first diversification and then multicellularity back. Diversification would have to wait for DNA and a deterministic genome compared to shorter RNA populations. DNA is chemically but not as thermally stable as RNA I think (difficult models to assess for a layman), so incessant heating selects RNA.

And multicellulars could have to wait for even lesser rates. A still significant impactor rate would promote dispersal between large scale sterilizations, so filamentous multicellulars may have been selected against under such conditions.

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