Estimado paisano Dr. Pérez-Pimienta,

No tengo mucha experiencia en el manejo de estas cepas de bacterias; tengo entendido que investigadores del CINVESTAV IPN (Zacatencoe Irapuato) tienen muchos y buenos desarrollos al respecto.

Saludos cordiales.

Estimado Dr. Claudio Chavarin,

Agradezco la información, esperemos continuar con nuestros esfuerzos y presentar resultados interesantes en la brevedad posible.

Saludos.

Well Jose, It is easy to get a strain of S. cerevisiea capable of fermenting C5/C6 sugars and of all xylose. The problem you will face (from my experience) is the ethanol concentration tolerance  I would go one step ahead and suggest that why don't you try and explore a bacteria like Zymomonas which might give better results.

You need to figure out how the yeast is able to ferment xylose. Most engineered strains have simply been supplemented with a couple of genes coding for a xylotol dehydrogenase, xylose reductase.. These do not work well because xylose utilization causes a redox (NADH/NADPH) imbalance in the cell. the dehydrogenase has NAD+ as cofactor.  Please see http://aem.asm.org/content/76/22/7566.full

I have heard of research into strains that instead have been supplemented with 3-4 bacterial genes that circumvent this problem. Not sure these are commercially available yet.  

Inhibitors such as acetic acid, furfural and other furan-compounds have a severe impact on most yeasts. They respond by having very long lag-phases before they start metabolising. This completely ruins the economy of most processes for fermenting lignocellulosic hydrolysates, even if it is technically possible.

One technique for increasing inhibitor-tolerance is to use flocculating yeasts, that express flocculin proteins, making the cells stick together in clumps.