Difference between revisions of "Team:Amsterdam/Project/Stability"

‘An elephant in the room: Obvious, important, yet largely ignored.’ That’s how Patrik Jones described the problem of genetic stability in this publication last year. The problem, in a nutshell, is that micro-organisms don’t like to allocate precious carbon resources to biofuel molecules or other human-desired compounds - they would rather use them to grow instead. Not literally so perhaps, but in most circumstances in the lab where organisms are cultivated, or in bioreactors of any form, species are under constant selection pressure for growth rate. After all, an organism that produces a compound and transports it out of the cell is forced to divide its resources between growth and product formation. As such, any resources that go into the making of a product are not allocated to its growth. A mutant that loses its production activity, however, will allocate more resources to growth, grow faster in comparison, and therefore take over a population in a matter of generations.

In practice, this means that novel gene insertions implemented to drive product formation often quickly accumulate mutations that render them inactive (sometimes a single mutation in a gene’s promoter is sufficient to do so). The result: bioreactor runs that often face sudden declines in productivity, a massive problem when it comes to large-scale implementation of bioproduction. Even many of the wonderful parts included in the iGEM registry would face this problem when scaled up in application. This is the problem of genetic stability: how stable is a producing strain when faced with the pervasise evolutionary pressure that selects for growth rather than productivity? Or, more specifically, how fast does a producing strain accumulate mutations that results in a decline or complete stop in productivity?

There is no easy way of solving this problem. Most biotech companies deal with it simply by re-innoculating their producing strain. Yet the costs involved in re-innocultion and lost production can add up to significant amounts. The problem is exacerbated when using cyanobacteria, the proposed pillars of the CO2-fixating, sustainable production processes of the bio-based economy. Their slow growth and naturally stronger tension between catabolism and anabolism make the problem both more costly and more frequent. After we demonstrated genetic instability in action in our lactate-producing Synechocystis strain, we therefore decided to make central stability one of the core aspects of our project and tried to create a stable carbon producer. Below is an overview of the different components - found separetely on the respective project page - that highlight our demonstration of genetic instability, the way we tackled the issue, and our evidence supprting that we indeed found a way to overcome it.