Wetenschap - 13 september 2012

Genetic variety through mobile switch

Bacterial gene strongly influenced by jumping on-off switch. MSc student's discovery leads to top publication.

The evolution of bacteria appears to be a faster and more complex process that hitherto believed. This conclusion was reached by MSc student Maria Matus-Garcia in the course of her final research project. The research, published in Nucleic acids research in August, focused on the 'on-off switch' in bacterial genes, known as the promoter. This little bit of code determines whether a gene is switched 'on' or 'off'. Genes needed for survival, for example, need to stay constantly switched on. Others are only needed if the bacterium is swimming in an acid environment or in the dark, for instance.
The researchers now show that these 'on-switches' an easily jump to another gene. With major consequences, as the switch can fundamentally change the function of a gene. For example, unused genes can suddenly be activated, which can have an impact on the organism. This can lead to the emergence of useful new varieties of the bacterium. By showing that genes can easily switch promoters like this, the research makes clear that the evolution of bacteria involves much more variety than was hitherto believed.
Chance
That promoters make leaps across genes was known anecdotally, research supervisor and assistant professor Mark van Passel explains. 'A colleague once sent by post bacteria that were negative for a certain characteristic. But when the people on the receiving end cultivated the bacteria, it was switched on again.' Van Passel's results now show that the process is actually quite common, even on short evolutionary timescales and in all kinds of different species of bacteria.
Exactly how the promoters make these leaps is largely unclear as yet. Van Passel has a few possible explanations. The promoters have a characteristic code, which suggests they hitch a ride on the activity of other mobile DNA.' Chance could also play a role. Van Passel: 'In view of the fact that we found 4000 of them, it is possible that they work according to various different mechanisms.'
MSc research published 
It is very unusual for the final thesis of a science student to get published, especially in a journal of the standing of Nucleic acids research. Mariana Matus-Garcia from Mexico managed this feat with her research in the department of Systems and Synthetic Biology. 'She was a very good student who really put her own stamp on the project', says her supervisor, assistant professor Mark van Passel proudly. 'She has been accepted all over the place now, Cambridge, Heidelberg, but in the end she chose the top university MIT.'

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