Creating Textbook Knowledge over Pizza
(September 3rd, 2015) The endosymbiotic theory has been around for nearly 150 years. And although it gives answers to many questions on evolution, some of them still remain unanswered. A recent discovery unlocks a handful of these mysteries and further supports the theory’s reliability.
How organisms have evolved on earth is an ongoing question for scientists all over the world. We are always fascinated to learn more about the giant dinosaurs that populated the planet before us, or the first single-celled organisms that started to make oxygen – the basis of our life. Decades of research allowed us discreet peeks behind evolution’s curtains. One of the most important discoveries was the endosymbiotic theory, proposed by a number of scientists over the last 150 years: Andreas Schimper, Konstantin Mereschkowski, Ivan Wallin, Lynn Sagan (nee Margulis) and others. The theory states that single-celled organisms possessing a nucleus (eukaryotes) fused with a bacterium (a prokaryote) and, due to the bacterium providing the eukaryote with all the machinery for energy production, a symbiotic relationship arose.
The theory, however, couldn’t provide answers to all questions and thus, scientists came up with alternative theories. However, a recent discovery by scientists from Germany, New Zealand, Ireland and England shows once again that the endosymbiotic theory is closer to reality than one might assume. Funded, amongst others, by the European Research Council, the article demonstrates that prokaryotes and eukaryotes have two separate systems to exchange genes: “Prokaryotes have several mechanisms for exchanging genes – phages, plasmids, natural competence – where in eukaryotes the main gene transfer mechanism is sex – meiosis – and this constrains swapping so that it is usually within-species,” shares James McInerney, co-author of the study and evolutionary biologist at the University of Manchester.
“We are very much interested in genetic mergings these days. Antibiotic resistance genes spread around the globe by being carried on plasmids, and new phenotypes arise all the time in prokaryotes and eukaryotes. How this happens is a big concern to us. If we eat GMO foods, will we take the DNA into our own genomes? All these questions are in the public domain. What our studies show is that we are unlikely to be really effective in preventing the spread of antibiotic resistance genes or at least we won’t be able to put up barriers to these mechanisms – they are extensive and they are continuous and the timescales are days and weeks and months. However, we can be more than happy that it is very unlikely that any foreign DNA will be incorporated into our own genomes – we simply do not do this on anything shorter than geological timescales,” adds McInerney.
The evolutionary biologist also explains how the thorough research was performed: “For the most recent work, the methods were entirely computational. We used completed genomes for approximately 2,000 prokaryotes and 55 eukaryotes. We performed all-versus-all homology searches and identified approximately 30,000 ‘clusters’, which are more-or-less equivalent to gene families. About 10% of these were found in both prokaryotes and eukaryotes. This 10% was the main focus of the research – trying to see what kinds of contributions to eukaryote genomes were made by prokaryotes and whether these contributions were made in a small number of big contributions or a large number of little contributions.”
So, how exactly are exciting discoveries like these made? “Slowly, slowly, slowly, then Eureka,” McInerney responds. “We had a Eureka moment in Düsseldorf in about April earlier this year, when Bill Martin showed me a predecessor to Figure 1 in our paper. He printed it out on giant sheets of paper, sellotaped it to a wall in the corridor and we stared at it for about an hour trying to figure out what it meant. Later that evening, we went to an Italian restaurant with Bill’s two kids and we had some pizza and in that hour or so, the ideas were firmed up. We have identified the major gene flows into eukaryotes and we can identify those genes most likely to have been in the ancestral eukaryote. This knowledge will soon be in student textbooks and is a fundamental understanding of biology,” James McInerney concludes.
You can watch James McInerney talk about the discovery here.