Sep
24
Human Microbes May Help Make Biofuel
September 24, 2014 | Leave a Comment
Researchers have looked far and wide for microbes that break down hemicellulose focusing over the past years on termite gut microbes because they breakdown wood tissues effectively and cow stomach rumens because those microbes break down the hemicellulose from grass plants quite well.
The UI scientist’s study has been published in the Proceedings of the National Academy of Sciences. The UI team’s work is the first to use biochemical approaches to confirm the hypothesis that microbes in the human gut can digest fiber, breaking it down into simple sugars in order to ferment them into nutrients that nourish human cells.
That seems to be a reversal of logic, but a longer look could consider that natural sugars, the food for yeasts that make ethanol, are very much the same as what humans need for energy in their diets. The new findings have significance for human health as well as for biofuels production, since the same sugars can be fed to yeast to generate ethanol and other liquid fuels.
Polypeptide Chain. Proteins consist of one or more polypeptides. A polypeptide is a chain of amino acids. The polypeptide chains fold into their final three-dimensional structure to constitute a functional protein. Click image for the largest view.
The human microbes appear to be endowed with enzymes that break down a complex plant fiber component more efficiently than the most efficient microbes found in the cow rumen.
University of Illinois animal sciences and Institute for Genomic Biology professor Isaac Cann, who led the new analysis noted their work in cows led the researchers to the human microbes. Cann also is a microbiology professor and a principal investigator at the Energy Biosciences Institute. A principal colleague is UI animal sciences professor Roderick Mackie.
Cann said, “In looking for biofuels microbes in the cow rumen, we found that Prevotella bryantii, a bacterium that is known to efficiently break down (the plant fiber) hemicellulose, gears up production of one gene more than others when it is digesting plant matter.”
When searching a database for similar genes in other organisms, the scientists found them in microbes from the human gut. The team focused on two of these human microbes, Bacteroides intestinalis and Bacteroides ovatus, which belong to the same bacterial phylum as Prevotella from the cow.
“We expressed the human gut bacterial enzymes and found that for some related enzymes, the human ones actually were more active (in breaking down hemicellulose) than the enzymes from the cow,” Cann said.
When the scientists looked more closely at the structure of the human enzymes, they saw something unusual: many single polypeptide (protein) chains actually contained two enzymes, one of which was embedded in the other. Further analysis of the most important protein revealed that the embedded component was a carbohydrate-binding module (CBM), which, as its name implies, latches onto carbohydrates such as hemicellulose. This enzyme shreds the plant fiber hemicellulose so that other enzymes can work on it to break it down into its unit sugars.
Working with UI biochemistry professor Satish Nair, the scientists also noticed that the CBM “put a kink” in the fiber when it bound to it. This bending action may bring the fiber close to the other enzyme in the protein so it can get to work breaking the bonds between the sugars. Further research is needed to confirm this hypothesis, Cann said.
The study points to human microbes as a potentially potent source of microbes that can aid in biofuels production. Cann said, “In addition to finding microbes in the cow rumen and termite gut, it looks like we can actually make some contributions ourselves. And our bugs seem to have some enzymes that are even better than those in the cow rumen.”
The news might not seem hugely significant, but it has been published in a very significant journal. Team member Dylan Dodd M.D. and Ph.D. student is now at Stanford University where biofuel work is a major effort. For all the looking far and wide a truly interesting and high potential and so far unique enzyme pair loaded into an effective and active polypeptide chains has now been found – up close, really close by.
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