Steven Brown, staff microbiologist in the Biosciences Division at the Department of Energy’s Oak Ridge National Laboratory and one of the inventors of the improved Z. mobilis strain explains, “Microbes have been breaking down plant material to access sugars for millennia, so plants have evolved to have very sophisticated cell structures that make accessing these sugars difficult.”

As the science stands in production now, biomass materials like corn stover, switchgrass and miscanthus must undergo a series of pretreatments to loosen the cellular structure enough to extract the sugar from the cellulose. Brown said these treatments add new challenges because, although they are necessary, they create a range of chemicals known as inhibitors that stall or stop microorganisms like Z. mobilis from performing the fermentation.

Brown said, “There are two ways to combat recalcitrance, or the difficulty created by the inhibitors. One way is to remove the inhibitors, but this method is very expensive and would not help biofuels become cost-competitive with gasoline. The second way is what we do, which is to develop microorganisms that are more tolerant of the inhibitors.”

The Oak Ridge team has for the first time identified a key Z. mobilis gene and shown the strain’s improved efficiency and its potential use for more cost-effective biofuel production.  The non-mutated strain of Z. mobilis cannot grow in the presence of one of the predominant inhibitors, acetate. However, when gene nhaA is over-expressed by inserting a slice of DNA containing the gene into the non-mutated strain, the bacterium can withstand acetate in its environment.  An open access paper on their work was published online 19 May in the Proceedings of the National Academy of Sciences. (Abstract link)

Round two!  Brown and lead author Shihui Yang did not stop with Z. mobilis but looked at related genes in other microorganisms and found that the method translates in different organisms. Yang said, “We took this gene and integrated it into a strain of yeast, and the improvements carried over into the yeast.”

Yang & Brown at their ORNL lab. Click image for more info.

Brown suggests this method of processing biomass for ethanol has the potential to become a “tool kit” – a combination of mutant genes that reduce the impact of specific inhibitors. The tool kit could expand quickly, too, as scientists now have more advanced DNA sequencing technology available to identify and resequence genes.  More broadly, the researchers say, their study shows that the application of biology systems tools holds promise for rational industrial microbial strain development. The combination of classical and biology systems tools used in their work is a paradigm for accelerated industrial strain improvement and combines benefits of few distinguishable types of propositional assumptions with detailed, rapid, mechanistic studies.  They believe they have a kind of lab test method coming up.

The Oak Ridge microbiologists are currently sequencing other microorganisms used in biofuels production that could also be advantageous if genetically altered to resist different types of inhibitors.

Brown said, “The DNA sequencer we used was unavailable as recently as five years ago, and it has unprecedented sequencing capabilities. It is 4,000 times more powerful than the machine that finished sequencing the human genome almost a decade ago.”

Yang looks further out, “By looking at the behavioral response to the genetic changes in this bacteria, Zymomonas, we can then look forward to improving other bacteria.”

It’s a good start.  Acetate is a major problem in conditioning cellulose.  Should the Oak Ridge team spread out the gene search perhaps the other inhibitors will fall as well.

Ethanol – the fuel many complain vociferously about – may be coming to a threshold of process development that could open up more plants as sources for production.  The use of cane sugar and corn in Brazil and the U.S. drive many to outrage over the idea of competition between foods and fuels.  While the issue is pointless, ethanol as a light alcohol has great potential as a fuel cell fuel, a gasoline additive and with other alcohols in gasoline substitutes.  The complaints are little but food for the foolish.

When researchers at the US Department of Energy’s Oak Ridge National Laboratory have identified a key gene that can yield more cost-competitive cellulosic ethanol the complaint matters will change course, probably to land use choices.  But the idea, a much wider source of plants to produce cellulose would bring more marginal land into productivity where farming is now a low net income proposition.


7 Comments so far

  1. jp straley on June 2, 2010 8:15 AM

    Always must be mindful that a microbe with the ability to radically outcompete wild-types could be a serious problem if it escaped. Best to assume that it will, in fact, escape. Best to assume it will share its modified genome with wild types so that you have normally-fit critters that can still utilize heretofore unavailable resources.

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