A Conversation With Bruce Rittmann, Sustainability Scientist


Rittman-Post.jpg Had he not grown up during the time of the first Earth Day and the Vietnam War -- and had those events not pushed him to want to make major improvements for society -- Bruce Rittmann might have used his degree in engineering to design bridges and other civic structures. Instead, he is working as the director of the Swette Center for Environmental Biotechnology at the Biodesign Institute at Arizona State University, and trying to find replacements for the fossil fuels we're quickly running out of. A leader in managing microbial communities (more on that later), Rittmann is also working to treat water and clean up pollution.

Here, Rittmann discusses a revolutionary innovation that directs photosynthesis to make fuel molecules as a potential substitute for petroleum; the ideal win-win situation, a partnership between microbial workers and human managers; and how working out in the gym has turned him on to country music videos and Reba McEntire.


As the director of the Swette Center for Environmental Biotechnology, I start by explaining environmental biotechnology. The description goes like this: I manage microbial communities to provide services to society. The services are at the core of water and energy sustainability. The water side involves improving water quality. Microorganisms clean up contaminated water so it can be used by humans or returned to support natural systems. The energy side means producing truly renewable forms of energy in ways that don't harm the environment. The "workers" in our service business are a wide range of microorganisms. Microorganisms are everywhere: on your skin, on your teeth, on river rock, and deep below the sea. Their normal metabolism -- eating and metabolizing what they've eaten -- provides all sorts of services that humans need. For them, biodegrading pollutants or producing fuels is simply part of their normal life. What we want to do is manage the microorganisms so that they provide the services reliably and at the necessary rate.

In our research center, we study microorganisms -- who they are, what they can do, what controls what they actually do, and how they interact with each other. The last item is important, because all practical systems contain many different types of microorganisms -- a community -- that work together to produce the services we desire. We study the microorganisms deeply so that we can think like them. Then, armed with this knowledge, we can work for the microorganisms so that they work for us. It is an ideal win-win situation, a true partnership between the microbial workers and the human managers.


I have to mention a revolutionary innovation that is part of our portfolio of microorganism-based energy. I call it the "photosynthetic factory." We've modified photosynthetic bacteria to enhance their ability to produce and excrete long-chain fatty acids. These fatty acids are the perfect precursors for transportation fuels, such as jet fuel. Potentially, this discovery could be a substitute for petroleum.

Photosynthetic bacteria -- also called cyanobacteria due to their blue-green color -- are one of the most ancient life forms on the planet. As the first oxygen-producing phototrophs, cyanobacteria are largely responsible for creating the Earth's oxygen-rich atmosphere, which is what makes it possible for the planet to have complex life forms, such as we humans.

Today, our team takes advantage of these simple bacteria by adding to their metabolic capacity the ability to produce long-chain fatty acids. Being photosynthetic, the cyanobacteria absorb sunlight energy and fix CO2 into organic molecules. Our strategy is to have them send a significant part of the organic carbon to long-chain fatty acids, which they excrete. We rapidly harvest the fatty acids, which are then readily convertible into the main components of jet fuel. In short, we are using sunlight, CO2, and cyanobacteria to make renewable transportation fuel.

This approach is novel -- even revolutionary -- because we direct photosynthesis to make fuel molecules, not to make more bacteria. While it is possible to harvest bacteria to make fuel precursors, the process requires difficult and expensive steps. By treating the photosynthetic bacteria as a sunlight-driven factory to make fuel, not as the fuel feedstock, we can bypass several difficult and expensive steps. Furthermore, we can train our photosynthetic factories to make many other materials that can be renewable feedstock of many kinds.

Our team is involved in all steps of the novel approach: modifying the photosynthetic bacteria, creating novel reactor systems to grow the photosynthetic bacteria and harvest the products, and converting the products to fuel.


I suppose most people don't appreciate two related things about managing microbial communities. The first is how we establish a win-win partnership with the microorganisms. We enable their metabolic capabilities; the end result is a high-value service for society. The second is that we always work with communities of microorganisms. We do not have some kind of super bug that works in isolation. Even when we emphasize a certain microorganism with special skills -- as with the photosynthetic bacteria in our photosynthetic factory -- it has microbial colleagues that we must understand and manage.


I am going to mention two emerging trends.

First, those knowledgeable about sustainability are realizing that we must find substitutes for about 70 percent of the fossil fuel we currently use. Human society worldwide consumes fossil energy at a rate of about 10 TW (terrawatts) today. This rate of consumption cannot be sustained due to the build up of atmospheric CO2, depletion of petroleum reserves, and political conflicts. To stop the increase of atmospheric CO2, we need to cut the fossil fuel use to about 3 TW. Where will we find 7 TW or more of renewable energy? At this scale, virtually all renewable energy must come from sunlight. Thus, society is going to need to make giant investments in a range of methods to collect and use solar-derived energy: photovoltaics, photosynthetic microorganisms, wind, and others.

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Nicholas Jackson is a former associate editor at The Atlantic.

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