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A question about Xylose production in E. coli B cells

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A question about Xylose production in E. coli B cells

Postby Sparks » Tue Apr 17, 2007 8:35 pm

Hello,

I am interested in the production of Xylose in E.coli B cells. I guess the gene(s) for Xylose are probably not present in the E.coli B genome, so a modification in the genome/plasmid is needed.

When this is done, how can the effect of the introduced modification be demonstrated and which fermentation process is suitable for the production of Xylose with the recombinant E. coli?

Thanks,
Tim
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Postby blcr11 » Wed Apr 18, 2007 4:27 pm

Boy, I really don't know how to suggest anything here. Does any bacterium actually make carbohydrate? They utilize sugars (including xylose), but that's catabolism, not anabolism. There's gluconeogenesis in animal cells and there are epimerases that might interconvert an array of sugars, but most of the anabolic reactions involving sugars that I'm aware of are in making cell membranes or polysaccharides of one sort or another. But to actually make xylose--from simpler units--I dunno, take a look at some plant metabolic pathways would be about all I can suggest and even there I kind of doubt there's a direct pathway to xylose. Xylose isomerase (which I thought E coli had) interconverts xylose and xylulose as well as glucose and fructose. The enzyme has been engineered and/or over-expressed in order to manufacture fructose from glucose, but it's not obvious to me how that helps to make xylose. Maybe there is a way from glucose to xylulose?
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Postby Sparks » Thu Apr 19, 2007 12:44 pm

Thank you for your reply blcr, i will look this up. There is also something not clear to me about fermentation, if there's said: "fermentation of xylose" what does this mean exactly. Does it mean the anabolism of xylose from other molecules, or does it mean the catabolism of xylose like in this pathway:
Attachments
xoferm1.gif
xylose pathway in yeasts
xoferm1.gif (1.27 KiB) Viewed 2510 times
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Postby blcr11 » Thu Apr 19, 2007 2:15 pm

To ferment a sugar usually means to have the organism--typically yeast or bacteria--use the sugar as its primary carbon source. The end product of anaerobic utilization is ethanol, hence the sugar ferments. This is a catabolic process. Yeast and bacteria are pretty good at utilizing whatever sugars happen to be around. Glucose, if it's around, will be the preferred source, but if xylose happens to be in abundance, they will happily turn on the xylose utilization pathways and go merrily on their metabolic way.
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Postby blcr11 » Thu Apr 19, 2007 3:13 pm

I guess I should add, the end product of anaerobic glycolysis is ethanol (from the reduction of pyruvate produced by passage through the citric acid cycle). Xylose will probably go through the pentose phosphate pathway and I'm not certain what the end product there is. One of the final products is GA3P, which could end up as pyruvate, but I'm not certain how the pathway actually is used.
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