Improve Hydrogen Production by Genetic Methods: Design a Better Nanomachine

FOCUS GROUP DESCRIPTION

Background

In our increasingly mobile but always-connected society, there is a need for better small energy storage and conversion devices to provide a remote power source exactly where it is needed and only when needed, for example in cell phones, remote sensors, or in-body implants such as pacemakers, medical sensing, or drug dispersal devices. As our planet’s fossil fuel supply diminishes and our concern for global warming, pollution, and other environmental costs of our current energy supply system increases, it is essential that we develop cleaner, more environmentally benign power sources as well. Ref 1 provides an overview of challenges in energy technology that could be addressed by nanotechnology. Miniature biofuel cells could be a means of converting stored bioenergy to power, or alternatively of harnessing hydrogen gas from inexpensive, readily available materials such as sea water for a source of fuel when needed.

Unicellular microorganisms are remarkably efficient at catalyzing a wide range of chemical reactions (Ref 2), such as fermentation, respiration, and photosynthesis, using a variety of electron donors and acceptors. Recently, researchers have been able to program cells in rudimentary ways to perform tasks not evolved in nature (Refs 3, 4).

Several types of algae and bacteria can produce hydrogen by photosyn-



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The National Academies Keck Futures Initiative Designing Nanostructures at the Interface Between Biomedical and Physical Systems: Conference Focus Group Summaries Improve Hydrogen Production by Genetic Methods: Design a Better Nanomachine FOCUS GROUP DESCRIPTION Background In our increasingly mobile but always-connected society, there is a need for better small energy storage and conversion devices to provide a remote power source exactly where it is needed and only when needed, for example in cell phones, remote sensors, or in-body implants such as pacemakers, medical sensing, or drug dispersal devices. As our planet’s fossil fuel supply diminishes and our concern for global warming, pollution, and other environmental costs of our current energy supply system increases, it is essential that we develop cleaner, more environmentally benign power sources as well. Ref 1 provides an overview of challenges in energy technology that could be addressed by nanotechnology. Miniature biofuel cells could be a means of converting stored bioenergy to power, or alternatively of harnessing hydrogen gas from inexpensive, readily available materials such as sea water for a source of fuel when needed. Unicellular microorganisms are remarkably efficient at catalyzing a wide range of chemical reactions (Ref 2), such as fermentation, respiration, and photosynthesis, using a variety of electron donors and acceptors. Recently, researchers have been able to program cells in rudimentary ways to perform tasks not evolved in nature (Refs 3, 4). Several types of algae and bacteria can produce hydrogen by photosyn-

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The National Academies Keck Futures Initiative Designing Nanostructures at the Interface Between Biomedical and Physical Systems: Conference Focus Group Summaries thesis or fermentation. Photobiological technology holds great promise; however, as oxygen is also produced, the technology needs to overcome the limitation of oxygen sensitivity of the hydrogen-evolving enzyme systems. Screening for naturally occurring organisms, which are more tolerant to oxygen, as well as creating new genetic forms of the organisms that can sustain hydrogen production in the presence of oxygen is currently being performed (from Ref 5). Biofuel cells have been reported (see Ref 6) achieving several hundred nanowatts of power, in which tethered biological enzymes at two electrodes first strip a hydrogen ion off glucose and then combine the H+ with oxygen to create both power and water. Nanotechnology is currently revolutionizing small battery technology—see for example Ref 7. The Problem Given the information provided above (and any other research you choose to conduct) your task is to provide a scientific plan to create a programmed microorganism or a collection of nanobiomachines that uses water or oxygen as an input and creates a local source of hydrogen gas for use as a fuel. Decide on your specific goal, keeping in mind the following questions: What will be the power or hydrogen gas generation requirements needed for powering a PDA or a pacemaker 5-10 years from now? (Ref. 8) What are the environmental, safety, temperature, longevity, anti-fouling, or other engineering requirements needed? How efficient can this process be? Are there fundamental limits? If so, what are they? What are the overall fuel cycle costs of such a proposed technology? How would this technology compare (cost, size, efficiency, safety, environmental impact, temperature range, ease of use, robustness, and reliability) to competing technologies, such as nano fuel cells or nanobatteries? Initial References 1. Nanoscience Research for Energy Needs, Report of a NSET workshop “Nanoscale Science and our Energy Future,” DOE (2004). A link to the full report is provided on DOE’s Office of Science homepage: http://www.sc.doe.gov/.

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The National Academies Keck Futures Initiative Designing Nanostructures at the Interface Between Biomedical and Physical Systems: Conference Focus Group Summaries 2. Newman, D., Microbial Mineral Respiration. The Bridge, Winter 2003. National Academy of Engineering, 33(4):9-13. http://www.nae.edu/TheBridge. 3. Weiss, R., The Bridge, Winter 2003. Challenges and Opportunities in Programming Living Cells. pp. 39-46. 4. Kobayashi et al., Programmable Cells: Interfacing Natural and Engineered Gene Networks. Proceedings of the National Academy of Sciences, June 1, 2004. 101(22): 8414-8419. 5. For an introduction to hydrogen generation, see: The Generation of Hydrogen, The Hydrogen Economy, U. Birmingham. Also see References 1 and 2 of Focus Group 10. 6. Service, R., Shrinking Fuel Cells Promise Power in Your Pocket. Alper, J., The Battery—Not Yet a Terminal Case. Science, May 17, 2002. 296 (5571):1222-1226. 7. Nanobatteries—http://radio.weblogs.com/0105910/2004/05/26.html http://www.newswise.com/articles/view/?id=500572. 8. International Technology Roadmap for Semiconductors, 2003, has power requirement projections for handheld devices in the section on RF and analog/mixed signal electronics. A link to the entire document can be found at http://public.itrs.net/. FOCUS GROUP SUMMARY Summary written by: Tonya Clayton, Graduate Student, Science Communication Program, University of California, Santa Cruz Focus group members: Tonya Clayton, Graduate Student, Science Communication Program, University of California, Santa Cruz Michael Darby, Warren C. Cordner Professor of Money and Financial Markets and Policy Studies, Department of Public Policy, University of California, Los Angeles David Eaglesham, Chemistry and Materials Science Chief Technologist, New Business & New Products Group, Lawrence Livermore National Laboratory Jason Hafner, Assistant Professor, Department of Physics & Astronomy, Rice University Kurt Krause, Associate Professor, Department of Biology, Biochemistry and Chemistry, University of Houston Conrad Masterson Jr., Nanotechnology Foundation of Texas Bradford Orr, Professor of Physics, Department of Physics, Director of Applied Physics, University of Michigan

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The National Academies Keck Futures Initiative Designing Nanostructures at the Interface Between Biomedical and Physical Systems: Conference Focus Group Summaries Henry I. Smith, Keithley Professor of Electrical Engineering, Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology Sarah Tegen, Editorial Associate, Proceedings of the National Academies of Sciences Peter Vikesland, Assistant Professor, Department of Civil and Environmental Engineering, Virginia Tech George Whitesides, Professor, Department of Chemistry, Harvard University Summary Tiny solutions for big problems Focus Group 8 proposed a novel, two-part approach to improving biological hydrogen production for local, off-grid energy generation. The overall goal was to use clean, renewable, and biodegradable resources and methods to reduce dependence on hydrocarbon fuels at a scale useful to small, remote villages. The general idea was to develop first “a better bug” to convert solar energy to harvestable hydrogen gas. The proposed approach draws on contributions from Mother Nature’s protozoans, bacteria and photosynthetic algae, assisted by high-tech methods from the biological, chemical, genetic, and pharmaceutical sciences. The improved, more robust organisms would then be put to work on-site within a nearly closed system aimed not only at hydrogen production, but also optimal utilization and recycling of by-products and end-products. The social process that generated this proposal over the course of 7 1/2 hours together was a rather nonlinear, synergistic one. It entailed periods of whirlwind group discussion—with topics ranging from bovine flatulence to melting igloos—punctuated by occasional retreat for individual or small-group research and reflection. It began with groping for problem definition on Friday. It culminated Saturday with a surprising emergence of the final proposal—a “weird hybrid” incorporating many “crazy” and initially disconnected ideas from the preceding far-ranging conversations. “I’m astounded,” said one group member in the immediate wake of the final session. “I called my wife and said, ‘I just saw an amazing two days.’”

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The National Academies Keck Futures Initiative Designing Nanostructures at the Interface Between Biomedical and Physical Systems: Conference Focus Group Summaries What’s the problem? Initially charged with designing and growing “a bacterial or cellular factory to perform electrolysis of seawater to create hydrogen gas,” Focus Group 8 devoted Friday’s initial 1-hour session to surveying the group’s range of expertise and defining the exact problem to be tackled. On board were representatives from biochemistry, biophysics, chemistry, economics, electrical engineering, entrepreneurial enterprise, environmental chemistry/engineering, nanotechnology, physical chemistry, and physics. (Longed for by weekend’s end were biologists of various stripes.) “What’s the problem?” became the morning’s mantra as the group struggled to define which pieces of the hydrogen-production maze to address. To help frame the conversation, the group considered scales ranging from cityscape (100s kW/day) to microscales appropriate for space applications or human implantation (αW/day). A variety of hydrogen-producing approaches were tossed up, ranging from the “pure biology” of hydrogen-producing green algae to the photoelectrochemistry of titania (titanium dioxide) semi-conducting nanoparticles. One “crazy, intriguing proposal” was to assemble a collection of hydrogen-producing enzymes, like biological “spare parts,” to crank away within a tiny liposome pouch. The group mused that significant contributions might come ultimately from developing a systems approach to hydrogen production and by-product utilization, rather than focusing on any single part of the production process. By lunchtime and session’s end, the group had decided to work on the problem of: local production of hydrogen gas on a moderate scale (on the order of 10 kW) based on a non-hydrocarbon source. A backyard in Somalia or remote Texas might be typical deployment sites. Crazy thoughts and cow parts Having narrowed the focus to moderate-scale hydrogen production—means yet to-be-determined—Focus Group 8 re-convened Friday afternoon to identify current bottlenecks that might yield to innovative approaches. Envisioning eventual depletion of hydrocarbon fuel resources, the group focused on methods driven ultimately by sunlight. The pros and cons of a variety of approaches were considered in a 10-way, Ping-Pong-style group discussion with frequent contributions from

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The National Academies Keck Futures Initiative Designing Nanostructures at the Interface Between Biomedical and Physical Systems: Conference Focus Group Summaries the World Wide Web. “Purely biological systems are self-replicating.” Good. “But, accumulated waste products eventually shut down the system.” Not so good. “But, wastewater treatment plants manage to keep such systems going.” Good. “But, biological ‘spare parts’ don’t have to be kept alive.” Even better. “But, biological parts in isolation don’t tend to function for very long.” Not so good. Occasional long silences and contributions prefaced by, “Here’s a crazy thought,” were characteristic of the afternoon’s conversation. The bottleneck issue of oxygen toxicity cropped up repeatedly. Hydrogenase, the enzyme responsible for biological hydrogen production, is inactivated by oxygen—which is typically co-generated during the hydrogen production process. It is the Achilles’ heel of biologically based hydrogen-generation methods. By afternoon’s end, two persistent notions had earned summary diagrams on the whiteboard. One included the novel use of hydrogenosomes, organelles found in some anaerobic protists and fungi. The other was larger in scale, laying out in concept a complete, nearly closed system powered by sun and wind energy, and generating usable hydrogen, oxygen, and fresh water. It incorporated the novel use of reusable cobalt salen to capture the problematic oxygen. One participant likened this approach to “dissembling a cow and selling every part.” At day’s end, the group disbanded with lingering questions about many practical issues, such as component stability, production capacity, and system efficiency.