Mind-Bending Microbes

March 8, 2011 |

New isobutanol-producing and protein-munching microbes from UCLA remind us that biofuels remain in the anything-but-static, eye-popping era of their development.

The Digest’s “mind-bending breakthrough” in-basket is overflowing this week with advances in the fermentation of protein into biofuels….

“Whoa,” you might say, “stop right there. Did you say fermenting protein into biofuels? You can’t do that.” Well, it turns out you can.

Which will be the central theme of today’s Top Story as we look at two different, but startling, discoveries bubbling up from scientific circles this week.

Beware the “biofuels are” crowd

We’ve said it before – beware of any sentence beginning with the phrase “Biofuels are…” unless the next word is “changing”. The science is changing the possibilities and potential outcomes so rapidly, that we are still very much in the Wild, Wild West phase of the industry, and attempts to construct policy on the basis of “biofuels are…” will be as foolish as attempting to paint a pastoral landscape while sitting atop a bullet train.

The key difference between biofuels and other renewables is the fact that they are based on a process rather than a source – geothermal forces do not change, the nature of wind does not change, the nature of sunshine or rivers do not change. That’s what they have in common with fossil reserves of oil, gas and coal – there is local variation in quality and quantity, but in all those other energy systems, you are working with a basic, static substance.

Not so with biofuels. There are a hundred different feedstocks without counting hard, and at least a dozen robust ways to make them even if you lump, say, companies like Amyris, LS9 and Gevo into one group under the heading of “microbial fermentation.” The magic bugs that do the heavy lifting in fermentation are as varied as you can imagine, which is to say they are limited only by imagination itself.

Given the thousands of protein-encoding genes in a typical advanced organism, the opportunities for variation in what life can produce from its genetic treasury is, to be frank, only partly explored.

The new feedstocks, and the new micro-bioprocessors

Genetic diversity impacts the statement “biofuels are…” in two ways. There is the more widely-known field of genetically modified feedstocks – the insertion of traits into grasses, grains and other organisms to improve pest resistance, water or nutrient take up, salt tolerance, or drought tolerance, to name a few.

The lesser-known, yet fast-emerging field, is in the modification of the proteins, bacteria, or microalgae that can do industrial bioprocessing in our behalf. Whether it is the enzymes that tease sugars out of cellulose, or ferment sugars into fuels.

Isobutanol from cellulose in a single step

It was just such an advance that was reported in Applied and Environmental Microbiology this week, when a team at UCLA led by James Liao, using consolidated bioprocessing, for the first time produced isobutanol directly from cellulose.

While cellulosic biomass like corn stover and switchgrass is abundant and cheap, it is much more difficult to utilize than corn and sugar cane. This is due in large part because of recalcitrance, or a plant’s natural defenses to being chemically dismantled.

Adding to the complexity is the fact biofuel production that involves several steps – pretreatment, enzyme treatment and fermentation – is more costly than a method that combines biomass utilization and the fermentation of sugars to biofuel into a single process.

To make the conversion possible, Liao and postdoctoral researcher Wendy Higashide of UCLA and Yongchao Li and Yunfeng Yang of Oak Ridge National Laboratory had to develop a strain of Clostridium cellulolyticum, a native cellulose-degrading microbe, that could synthesize isobutanol directly from cellulose. “This work is based on our earlier work at UCLA in building a synthetic pathway for isobutanol production,” Liao said.

While some Clostridium species produce butanol, these organisms typically do not digest cellulose directly. Other Clostridium species digest cellulose but do not produce butanol. None produce isobutanol, an isomer of butanol.

While there were many possible microbial candidates, the research team ultimately chose Clostridium cellulolyticum, which was originally isolated from decayed grass. Clostridium cellulolyticum has a sequenced genome available via DOE’s Joint Genome Institute.

Compared to ethanol, higher alcohols such as isobutanol are better candidates for gasoline replacement because they have an energy density, octane value and Reid vapor pressure – a measurement of volatility – that is much closer to gasoline, Liao said.

The protein-munching, fuel-spitting microalgae

Even more startling, another UCLA research team led by Liao and postdoctoral student Yi-xin Huo, reporting in this week’s issue of Nature Biotechnology, said that they have developed to utilize proteins as a feedstock for industrial bioprocessing and for biofuels.

That’s right, protein. Not the carbs or the fats that have been used to date.

In the world of, say, microalgal production, a lipid content of 25 percent is considered a pretty target for a strain that is accumulating biomass at the rate of say, 25 grams per square meter per day. Then there are the carbohydrates – that is, the sugars – maybe 5-10 percent. Leaving 65-70 percent protein content.

To date, almost every biofuels developer on the earth that is utilizing lipids has a clause in their business plan referring to the high-value of the proteins as animal feed. Of course, skeptics have asked how much value there would be in those proteins after millions of tons of them are dumped onto the market, in scaled algal biofuels deployment, in the absence of a suitably vertical increase in protein demand.

And consider that, for every billion gallons of algal based biofuels made from algal oil, there would be 8 million tons of algal protein to dispose of in some way. To put that in perspective, consider that the US utilizes about 150 billion tons of grains each year for feed.

So the potential – at proof of concept stage right now – to utilize proteins as a fuel feedstock is a materially interesting option.

Now, let’s keep this in some perspective before every gasification-based biofuels company storms the Digest’s offices. You can gasify biomass, already, and thereby convert the entire biomass to hydrogen and carbon monoxide, and ferment or catalytically convert that gas stream into biofuels. That’s how Coskata, LanzaTech and Virent, more or less, proceed. But it is also the path of Range Fuels, which offers a cautionary take – or the Fisher-Tropsch fuels that have had a tough time getting financed.

But the concept of fermenting protein itself is novel, and demonstrates the vitality and turbulence of biofuels development, Bringing us back to the point about being mighty wary of anyone who begins a biofuels critique, or a rave, with “biofuels are…”.

Protein magic

Here’s how the team at UCLA is doing its protein magic. First of all, they start with microalgae.

“Microorganisms tend to use proteins to build their own proteins instead of converting them to other compounds,” Yi-xin Huo told Science Daily. “So to achieve the protein-based biorefining, we have to completely redirect the protein utilization system, which is one of the most highly regulated systems in the cell.”

Well, that’s easy to understand. As humans, we get fat when we eat carbs, but when we add a lot of protein to diet and get the right sort of exercise, we bulk up.

The opportunity, turns out, is not in the carbon, but in the nitrogen – or rather, in the ammonia which is a component part of your everyday protein.

Nitrogen neutrality: not just a dream?

So in  this case, the team created a revised metabolic pathway. In protein, you have carbon and ammonia (ammonia is primarily nitrogen, and the reason we need to use so much nitrogen fertilizer to make biomass – the organism wants to make protein). In this case, the researchers developed a new pathway that makes a protein, then robs the ammonia and recycles the nitrogen back to make more protein. Leaving the carbon to be captured for biofuels and chemicals – and thereby creating a system which is, to come extent, nitrogen neutral as it grows.

Nitrogen neutrality. Now that is a very, very interesting concept, as we look at the fossil fuel intensity of biofuels feedstocks, and the issues of nitrogen run-off. There are cost opportunities, and environmental opportunities a-go-go.

Not ready for prime time

It’s all at the proof of concept stage – harvesting the protein biomass in an economically-viable manner is a subject for future research – which is to say, this isn’t a technology ready for prime time.

But it illustrates the vitality of the field. Our ideas of how to make feedstocks are radically changing. And it turns out that our ideas of how to capture and store that energy is radically transforming as well.

That’s what continues to make bio the most confounding and lively of all the energy arts.

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