A Conversation With Bruce Rittmann, Sustainability Scientist

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.

What do you say when people ask you, "What do you do?"

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.

What new idea or innovation is having the most significant impact on the sustainability world?

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.

What's something that most people just don't understand about your area of expertise?

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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.

What's an emerging trend that you think will shake up the sustainability world?

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.

Second, energy is not the only fossil resource that is used on a massive scale and for which we need to find a substitute. Perhaps even more pressing is mined phosphorus (P), which is part of the foundation of modern high-yield agriculture. The time horizon for depleting P reserves is even shorter than that for petroleum, and we have no obvious replacement. Phosphorous is the backbone of all living things. Therefore, society must find some way to make the agricultural use of P much more efficient; this will include finding technological means to recover what I call the "lost P" from crops and animals.

What's a sustainability trend that you wish would go away?

It is important to remember that the issue of sustainability is mostly about sustaining human society. It is not about sustaining the Earth or nature. The Earth and nature do not need human beings to survive. Instead, humans need to live compatibly with Earth and nature. A misguided trend is focusing on something like saving the planet. Once humans wake up to the fact that sustainability is all about saving ourselves, we will get serious about making the kind of investments we must make.

What's an idea you became fascinated with but that ended up taking you off track?

I have found that I have to de-emphasize some things so that I can put my energies on my highest priority goals. Not doing this kind of prioritizing could lead me to get off track. One thing I have done recently with the de-emphasis strategy is to turn over leadership of our Center's research on microbial electrochemical cells to my younger colleague, Dr. César Torres. César is, in my opinion, the top researcher in the world in the exciting new area of microbial electrochemical cells; so, all things are better with him in the lead.

Who are three people or organizations that you would put in a Hall of Fame for your field?

I begin with my Ph.D. advisor at Stanford University, Dr. Perry McCarty. Perry decided to take a chance on me as one of his graduate students. I learned so much from his way of thinking about the microbial world and his style of working. He is without question the father of what we now call environmental biotechnology. I am proud that he and I wrote a textbook called Environmental Biotechnology: Principles and Applications.

Next is Dr. David Stahl, now a professor at the University of Washington. In the mid-1980s, David and I were young professors at the University of Illinois at Urbana-Champaign. David was newer and knocked on my office door one day in an attempt to find colleagues. He explained what he did, which is about interrogating the genetic information of microorganisms to find out who they are. I had never heard of anything like this, but I quickly realized that his skills would transform our field. Seeing that opportunity had knocked -- literally -- I immediately began working with David. He and I introduced molecular microbial ecology to environmental engineering, and it is now the heart of all advanced research in environmental biotechnology.

Third is Dr. Willem Vermass, my colleague at Arizona State University. A year into my time at ASU, I was invited to a meeting to identify interesting research directions. We were getting ready to present our ideas to the CEO of BP. Wim talked about his work with cyanobacteria; he is one of the world-leading researchers in this area. Although I never worked with cyanobacteria before, I quickly saw that combining his expertise with cyanobacteria with my expertise with microbial reactors opened up a whole new world -- the chance to generate massive amount of renewable energy from the sun. We began working together, obtained funding from BP, and eventually evolved our work to the photosynthetic factory. I am eager for the next steps.

What other field or occupation did you consider going into?

My undergraduate degree is in civil engineering. If I'd been more interested in structures, which is a mainstay of civil engineering, I could be designing bridges. However, I was an undergraduate in the early 1970s. This was the time of the first Earth Day and the Vietnam War. Both had a profound impact on me and led me to look for a calling that could have a positive impact on society. This made me open to environmental engineering and eventually environmental biotechnology. More than anything else, I was presented with wonderful opportunities and grabbed them.

What website or app most helps you do your job on a daily basis?

Nothing comes to mind here. Graduate students are a lot better than apps.

What song's been stuck in your head lately?

Most of the cardiovascular equipment at the gym now has a TV, and I sometimes watch the music stations while exercising. I discovered that the country music station has by far the best videos and that some of the performers are really good. At the top of my favorites list is "Consider Me Gone," by Reba McEntire.