TotM: Yeast Dihydroorotate dehydrogenase, gifts and adapting to a new home

lamppost_snow.jpgHello everyone! Since we are getting close to holidays I’m going to get a bit more personal than usual. Fear not, as the evolutionary tale of the month will still be published. I will start saying that, unsurprisingly, I am a scientist. You, the reader, probably are a scientist too. I would guess that you have some interest in molecular evolution of some sorts. Our profession is one driven by passion and curiosity. Unfortunately, it is also one which forces many people to leave their homes away for long time. Any laboratory has, or has had at some point, many people that has come from a more or less distant land. I guess is a natural part of the process. Lots of scientist like me, and probably you, will travel this month to meet again their families and their old friends, to share some time with people we care about. But I don’t want to focus on that right now. Rather, I want to think about how we adapt to a new environment.

Fortunately for scientists we are surrounded by people in the same situation as us, and in my experience it is very common to find new friends, even good friends, in other members of your institution. I think that friendship can arise anywhere, and while you may miss your old friends you actually feel less alone than you would have thought the first time you put a foot in your new city. Furthermore, cultural differences are quite exciting. It depends on the person, of course, but scientists are usually fairly curious by nature and thus learning a new language or discovering new customs is a challenge that, while sometimes tough, is generally welcome. I don’t want to touch delicate subjects such as xenophobia. I’ve been fortunate to not suffer anything like that, and I’m quite sure many people has terrible experiences after finding bigotry in their new homes, but today I want to keep things mostly cheerful. Having said that, I think the most difficult part of finding a new place to live is actually the small details. Maybe you miss some kind of kitchen hardware that is very common in your country. Or something about how your new neighbours catch the bus feels out of place. Maybe you found that something very essential for you is now an exotic luxury or perhaps your favorite TV show now has a really weird voice acting. However, just like the little details are the ones that make you feel far from home, they can also be the ones that make you feel like that new place is truly yours. New habits will arise. New things will be discovered. New homes will be created.


320px-Westfield_winery_baskerville_gnangarra.JPGLiving beings must adapt to new places to live, too. And just like us, sometimes the difference between living “on” a place and living “in” a place can be very subtle. A small gift from a friendly neighbour, in the form of some horizontal gene transfer, may turn a hostile environment into a new home. This is the case of the dihydroorotate dehydrogenase of Saccharomyces cerevisiae and other related yeasts. Thanks to their mitochondria, eukaryotes have a nice edge when living exposed to the oxygen rich atmosphere of our planet. They can tolerate being exposed to low anoxic environments more or less successfully, but it is not a condition most eukaryotes are excited to face. Yeasts in the Saccharomycotina clade are an exception, being quite comfortable at a great range of oxygen concentrations, to the point that losing mitochondria is not immediately lethal. This tolerance is a highly valuable trait for many industrial processes, where Saccharomyces is one of the biggest players.


yeast.gifThe gene was acquired from a bacteria long ago, before the split of the Saccharomyces genus. In our tree of the month, we can observe the weird taxonomic placement of the sequence, hinting at some instance of horizontal gene transfer. Unfortunately the species sampling is not the best to properly infer the details of the event, but we can observe that the sequence in S. cerevisiae is far away from the sequences in Candida albicans and Yarrowia lipolytica, the two other members of Saccharomycotina presents in the tree. The enzyme catalyzes the first step in the de novo pyrimidine biosynthesis pathway and thus is essential unless the culture medium is properly supplemented. Such an important gene is present in most eukaryotes. But it has a fatal flaw: The gene is linked to the electron transport chain in the mitochondrial membranes. Yeasts have solved this issue by acquiring a bacterial version of the gene that is expressed in the cytoplasm, and is thus free of the mitochondrial function. With this little gift, they have been able to colonize anoxic environments. In fact, S. cerevisiae has lost the mitochondrial version, having fully embraced its new home. Obviously there much more than that in this process. But for now let’s just remember that the small details are important, too.




Lamppost in snow in Madison Square Garde. Photography by David Berkowitz. Creative Commons License 2.0

Winery. Photography by Gnangarra, Creative Commons license 2.5