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Improving biofuel production thanks to yeast

12 Sep

Pastry

Everybody knows humankind produces beer and wine since ever. In this case, we put a bug – yeast, from the same family as the one helping to produce the nice pastries on the figure on the left  – in presence of sugar and absence of oxygen which concludes in the production of bioethanol.

Biofuels are a wide range of fuels which are in some way derived from biomass.When people think of producing some liquid biofuel, it is generally alcohol-based, namely bioethanol. People like it because it is renewable energy. It can be made from agricultural feedstocks (sugar cane, maize, potato). The problem is that if we use these crops, the food prices will increase and moreover, lot of arable land is needed; but most of all, the concerns went to the energy required to keep the pollution balance of the whole cycle of ethanol production (especially when it comes from corn).

Good news: recent developments with cellulosic ethanol production and commercialization may allay some of these concerns. Cellulose fibers are a major and universal component of plant cells and can be used for ethanol production: the biofuel which will result will have smaller carbon footprint and every plant can be used to produce it, meaning there will be no increase on food stocks. It seems quite idyllic but it is not: besides the cost (elevated…), the technology is not clear yet. The thing is that every plant has its own enzymes to process cellulose fibers. So, somehow, bioethanol industrials will need to have an « enzyme kit » and apply it to the plants to – make a long story short – breake the cellulose and transform it into alcohol.

A paper came out in Science several days ago titled Cellodextrin Transport in Yeast for Improved Biofuel Production. The authors show that reconstructing the Neurospora crassa cellodextrin transport system in S. cerevisiae (yeast) makes the latter grow very efficiently on cellodextrins. Furthermore, the authors performed some fermentation experiments and demonstrated that these engineered yeasts convert cellulose to ethanol more quickly than yeasts without this system.

How does it work? Cellulose fibers are very long chains that need to be cut into smaller pieces to be able to go into the metabolic pathways of the cell. So, dedicated enzymes make these pieces which are afterwards turned into individual sugars the yeast can digest. N. crassa is a fungus which likes cellulose a lot and grows happily on it partly because it can import the small pieces of cellulose inside the cell and transform them into assimilable sugars. The authors identified the genes in N. crassa which are responsible and transfered them into a yeast strain. Furthermore, a system is designed in order to include the cellulose pieces into a reaction which directly gives ethanol. The authors declare this system has obtained 85% of the expected ethanol production. They are thus very confident these engineered yeasts will help into overcoming the production of biofuels from cellulose and, in term, help make these fuels industrially viable.

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Publié par le 12 septembre 2010 dans Science

 

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