Researchers from the University of Tsukuba, Japan, in collaboration with East China Normal University, show that Escherichia coli cells become spherical when grown in conditions mimicking a primordial environment.
Image by Maximillian cabinet/Shutterstock
The point of this piece of research is not only what it tells us about the probable morphology of the earliest cells but what happened next.
It has long been assumed that the earliest cells would have been the simplest structures for maximal exchange of nutrients and waste with their environment and this would have been small spheres, since these give the maximal surface area to volume ratio. However, that remained an assumption until this experiment showed how a primordial environment would have favoured it.
The really interesting thing, however, is how the resultant organisms continued to diversify into, in this case, six distinct lines, with different sets of mutations all being selected to give the same advantages in that environment. This is perhaps best explained by the Tsukuba University press release:
Primitive cells are thought to have been spherical, but experimental evidence supporting this belief remains elusive. Now, however, researchers from the University of Tsukuba, in collaboration with East China Normal University, have shown that E. coli bacteria grown in a primordial-like environment become spherical.Creationists contend that these adaptive changes must be the result of intervention by their putative intelligent [sic] designer because nothing happens without its purposeful intervention. The problem for that childish notion is that here we have an example of six different ways of achieving the same result in the six different evolutionary lines of descendants from the original rod-shaped E.coli, resulting in the optimal spherical design for the given environment. Some of the lines achieved it through modifications to the cell membrane, whilst others achieved it through modifications to internal processes. Three of the six lines resulted in modifications to the same gene (crp) which is concerned with the transcription of DNA into functional RNA.
Our team grew these bacteria in an OAV environment and found that as the cells better adapted to the new conditions, they grew more quickly, became spherical, and decreased in both size and area-to-volume ratio compared with the original parent cells (Ori cells). Even when we relocated these evolved cells (Evo cells) to a glucose environment, they maintained their new spherical shape.The primordial environment on Earth is thought to have consisted of vesicles, or compartments, of fatty acids. Oleic acid is the most common fatty acid in nature and can be metabolized by E. coli. The team therefore mimicked primordial conditions by growing six different lineages of cells in an environment where the only available nutrient was oleic-acid vesicles (OAVs), rather than the more usual glucose sugar.
Professor Bei-Wen Ying., senior author
Graduate School of Life and Environmental Sciences
University of Tsukuba, Ibaraki, Japan
E. coli's usual rod shape allows rapid growth and nutrient uptake. However, their shape can change in response to their environment, turning into a filament when starved of nutrients.
The six different lineages of Evo cells all evolved to adapt to the OAV conditions without common mutations. Notably, two distinct strategies were observed: some cells developed mutations that directly targeted the cell wall so that the cell structure became spherical, while others accumulated mutations in other biological processes.
[modifications to the crp gene] implies that transcriptional regulation by crp may be crucial for E. coli to use carbon sources effectively.Three of the six lineages developed various mutations in the common crp gene. The protein product of crp acts as a regulator of transcription, the process by which the genetic information in the DNA is turned into a molecule known as RNA.
Professor Bei-Wen Ying.
This work is the first to show typically rod-shaped cells shifting to a spherical shape in a primordial-like environment, supporting the theory that when life began to evolve, the earliest primitive cells were spherical.
The embarrassing thing for Creationists is that the organism involved is one of their favourites, being the one Michael J Behe used to launch the Deception Institute's Intelligent [sic] Design hoax by misrepresenting the known science explaining the evolution of structures such as the flagellum of E. coli, so ID advocates are now obliged to claim that E. coli is the result of intelligent intervention by their putative creator god.
Genome mutations detected in the six Evos are indicated. The essential genes are indicated with asterisks. The genes that played a role in the cellular structure and the cellular protein abundance are highlighted in red and blue, respectively. The mutated gene that appeared in multiple lineages is in bold. The cell shapes of the original and evolved E. colicells are illustrated at the bottom.
So far as science is concerned, the experiment, in which diversification would be expected, simply added support to the intuitive assumption that the earliest cells were probably spherical. Naturally, in scientific circles where the TOE is the fundamental theory, diversification would have been expected, but the drivers of this diversification are nevertheless interesting in themselves and may tell us about the pressures early simple cells would have been subjected to and why they diversified into the branches we now observe.
The research team's paper is published open acess in the journal Communications Biology:
Here we have as good an example as you can get of how organisms diversify by natural selection acting on random mutations and how descendant lines develop because the process can only add to what has gone before and is not significantly reversible. It also highlights the infantile nature of ID creationism in that no intelligent designer would be constrained by its earlier designs which were the result of random, trial and error changes, and so end up with multiple solutions to the same problem, all from the same starting point.Abstract
The morphology of primitive cells has been the subject of extensive research. A spherical form was commonly presumed in prebiotic studies but lacked experimental evidence in living cells. Whether and how the shape of living cells changed are unclear. Here we exposed the rod-shaped bacterium Escherichia coli to a resource utilization regime mimicking a primordial environment. Oleate was given as an easy-to-use model prebiotic nutrient, as fatty acid vesicles were likely present on the prebiotic Earth and might have been used as an energy resource. Six evolutionary lineages were generated under glucose-free but oleic acid vesicle (OAV)-rich conditions. Intriguingly, fitness increase was commonly associated with the morphological change from rod to sphere and the decreases in both the size and the area-to-volume ratio of the cell. The changed cell shape was conserved in either OAVs or glucose, regardless of the trade-offs in carbon utilization and protein abundance. Highly differentiated mutations present in the genome revealed two distinct strategies of adaption to OAV-rich conditions, i.e., either directly targeting the cell wall or not. The change in cell morphology of Escherichia coli for adapting to fatty acid availability supports the assumption of the primitive spherical form.
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