F. Summary and Future Plans
In less than 30 months, the MBGC project has provided a tangible proof for the concept of a Grand Challenge project that has capitalized on the unique large-scale facilities at EMSL. Today’s genomics based systems biology projects in general need collaborations between scientists and technologists in diverse disciplines. The MBGC research group has evolved into a cohesive team that has wonderfully adopted the central philosophy of interaction and interdependence large-scale biology projects. During this project period, Cyanothece 51142, a relatively unknown cyanobacterium, has emerged as one of the most attractive bacterial systems to study circadian rhythms at various levels of physiology, metabolism, and structure. A testament to this assertion is the recent funding of two independent projects, one at PNNL and one at Boston University, by the DOE-GTL program to study aspects of Cyanothece 51142 biology that are complementary to those in MBGC. In addition, as described earlier, the same program last year approved a proposal from Principal Investigators Himadri Pakrasi and Louis Sherman to sequence six additional Cyanothece strains that have been isolated from different ecological niches all over the world. This effort is already underway at DOE’s Joint Genome Institute (JGI). Together, these activities have transitioned the initial research objectives of MBGC to a much broader level, and it is conceivable that in the near future, a Cyanothece collaboratory will be formed to provide a forum for interactions between all researchers working on Cyanothece.
The future goal of the MBGC project will be to use different Cyanothece strains for CO2 assimilation and bioenergy production. All current biofuel enterprises result in the production of copious quantities of CO2. Although conversion of plant feedstock to CO2 as a waste product of biofuel fermentative processes may be considered a carbon neutral process, the amount of CO2 produced will be staggering, as biofuel production becomes a viable source of energy. Thus, at the least, it would be incumbent to consider processes that might use CO2 as a viable starting material for the synthesis of value-added products. At the most, if the bulk of the CO2 produced could be “bioassimilated” on a large scale, an important contribution towards decreasing the amount of CO2 emitted into the atmosphere would result.
Photosynthesis is the ultimate source of all fossil fuels. It has been the dominant energy conversion and storage process on Earth for at least three billion years. It has been fine-tuned by evolution so that photosynthetic organisms are ubiquitous in nearly every known habitat that supports life and forms the basis of essentially all food chains. Given the success of photosynthetic organisms as living solar energy conversion systems, it is natural that they be investigated as vehicles for providing energy for human use, either directly or as the inspiration for biomimetic systems. The products of energy storage in natural photosynthetic organisms are used primarily for cell growth and reproduction. The production of large amounts of easily harvestable, high-energy products is not usual in natural microbial photosynthetic systems. For this reason, the use of genetically manipulated organisms in which a large fraction of the stored energy has been diverted into nonnative metabolic pathways is attractive. This will require that any large-scale production facility use closed bioreactors to avoid the introduction of genetically engineered organisms into the environment. Closed bioreactors are also highly desirable in terms of water use characteristics, as water loss is minimal in such systems. This permits them to be sited in arid environments that are unsuitable for either traditional crops or open pond systems. Long-term energy farming applications such as energyplexes will certainly use such environments in order to be economically feasible.
An appealing aspect of the use of photosynthetic microorganisms is that they do not produce macroscopic structures with robust mechanical properties, such as lignocellulose, that need to be broken down to recover the stored energy. The basic mechanisms of light-energy capture and primary photosynthetic energy storage are essentially the same in all photosynthetic organisms, so any system in which the cellular complexity is low is attractive. In principle, a large fraction of the biomass in such microbes is easily recovered as usable fuels, or organisms can be engineered to produce recoverable fuels such as hydrogen or liquid alcohols. Another advantage of photosynthetic microbes is that they are easily genetically manipulated. Genome sequences for many Cyanothece strains will soon be available, and robust systems are being developed for stable introduction and expression of foreign genes from a variety of sources.
The primary challenges to using photosynthetic microorganisms in bio-energy production are in selecting suitable organisms, engineering them to produce the appropriate easily recovered high-energy products, as well as developing efficient and cost-effective production facilities, such as photobioreactors. In this project, we plan to use oxygenic cyanobacteria.
Future Research Directions and Needs
- Use Cyanothece strains as model prokaryotic photosynthetic organisms to develop a detailed understanding of phototrophic prokaryotic energy conversion and CO2 utilization systems.
- Adopt a systems biology approach to understand the regulation of metabolism as a function of environmental conditions. It is important to develop a Cyanothece strain as a laboratory model so that we can determine the important characteristics needed when seeking new organisms in nature.
- Apply molecular biology and genetics to construct organisms with appropriate metabolic properties. For example, development of strains with higher ethanol production, more lipid storage for biodiesel production, higher levels of H2 evolution and more metabolite storage.
- Culture of Cyanothece strains to harvest the solar spectrum from 400 nm to 900 nm for the production of metabolites such as biodiesel and H2.
- Develop the energyplex concept. A long-term goal is to develop the cyanobacterial system for use as part of an energyplex that will integrate recycling CO2 from a power generation facility. The Cyanothece cells will use photosynthesis to first-capture carbon and then use the reduced carbon for the production of biofuels and other valuable compounds.