Zymomonas mobilis is a creature of habit, a bacterial species that loves to eat simple sugars and produce ethanol, but shows little interest in anything else.
“If you think about it, what are most biological organisms trying to do at any given time? They’re trying to reproduce as much as possible, right?” says Michaela TerAvest, an assistant professor of biochemistry and cellular biology at Michigan State University and researcher at the Great Lakes Bioenergy Research Center (GLBRC). “The weird thing about this one is that it doesn't grow very well at all.”
But TerAvest also sees possibility in Z. mobilis’s singular focus on ethanol production: when it’s stacked up against other bacteria that convert biomass to biofuel, such as Saccharomyces cerevisiae, it is significantly more efficient in converting glucose, the simplest of plant sugars, into fuel. Finding a way to tap this efficiency could help TerAvest and her GLBRC colleagues lower the cost of making sustainable biofuels and bioproducts.
The challenge lies in diversifying Z. mobilis’s palate. That includes convincing it to eat other types of plant sugars and to produce advanced fuels such as isobutanol, which can be dropped into current gas tanks without modifications to the engine.
“We’re finding that if we want to get it to make anything other than ethanol or use a food source other than the sugars it’s used to, it’s actually a lot harder to change than other organisms,” says TerAvest.
Bacteria are so much faster than anything else to study. You can start an experiment one day and have an outcome the next.
Michaela TerAvest
For TerAvest, who holds a Ph.D. in biological and environmental engineering from Cornell University, the best way to figure out how something works is to break it. That means first manipulating genes in Z. mobilis to slow down conversion of sugar to fuel. There’s a practical reason to break this function too. “If we understand how to turn this behavior on and off,” says TerAvest, “we can speed up the growth stage early in the industrial process, then switch into production stage when we want them to make all that fuel.”
Working with Jennifer Reed, University of Wisconsin–Madison associate professor of chemical and biological and chemical engineering, TerAvest’s team looks for growth genes in another biofuel producer, E. coli. Reed then runs models to determine which of these genes, when added to Z. mobilis, would make the bacteria reproduce faster while also slowing down its fuel production.
So far, the uniqueness of Z. mobilis is reflected in its willingness, or lack thereof, to take on new genes. “It really does not like foreign DNA,” says TerAvest, describing how the bacteria merely chops up unidentified genetic pathways. “It’s uncommon for bacteria to be so resistant in this way.”
But TerAvest suggests that the bacteria’s small genome – the fact that there isn’t much there for scientists to alter – might also be what has made it so successful in quickly making ethanol. “We think that part of its strategy in being so fast is that it doesn’t keep anything extra around to get distracted by other pathways,” says TerAvest.
Cracking the bacteria’s genetic code will be a challenge, but TerAvest is buoyed by the very thing that first brought her to studying microbes: her own penchant for quick results. “Bacteria are so much faster than anything else to study. You can start an experiment one day and have an outcome the next.” When the right information falls into place, TerAvest says, Z. mobilis breakthroughs could come fast.
GLBRC is one of four U.S. Department of Energy Bioenergy Research Centers created to provide scientific breakthroughs for a new generation of sustainable, cost-effective biofuels and bioproducts. For more information on GLBRC, visit www.glbrc.org or visit us on twitter.