The report—Microbial Energy Conversion—primarily highlights the use of microbes to produce alternative fuels. The report describes in detail the various methods by which microorganisms can and are being used to produce fuels including ethanol, hydrogen, methane, lipids, and butanol. It also discusses the advantages, disadvantages and technical difficulties of each production methodology as well as outlining future research needs.

There is a pronounced need to study and understand the biology of the microorganisms currently used in bioethanol production. For example, mechanisms of product toxicity in microbes used in consolidated bioprocessing systems, like Clostridium thermocellum, require further research. The enzymology of biomass depolymerization (the breakdown of recalcitrant, multi-unit compounds into smaller compounds) also requires intensive study in order to optimize this process.

The report notes that future research in alcohol production needs to focus on increasing the productivity and yield of processes that make alcohol from biomass and processes that generate alternative, higher molecular weight alcohols such as butanol.

Hydrogen, a potent energy carrier, may be produced in any of a variety of ways. Oxygenic photosynthesis in cyanobacteria and other microbes can be harnessed to make hydrogen from water in a promising technology that may meet energy needs in the long term. The resources needed for this process, water and sunlight, are in practically unlimited supply, but the efficiency of the process is low. We need new photobioreactor designs to help increase efficiency of light capture and hydrogen removal in these systems. Hydrogen also may be produced using the cellular machinery of nitrogen fixation, through fermentation of biomass, through iron metabolism in photosynthesis, by metabolizing carbon storage compounds, or by microbial mats.

Methanogenesis, the report notes, is a relatively simple, predictable microbial process, and methane fits into the infrastructure in place of natural gas. However, much of the current data have derived from operations optimized for waste disposal, not for methane generation. Research in methane production should focus on optimizing the productivity of methanogenic microbial communities and bioreactor design.

Another technology that falls under the heading of microbial energy conversion is the microbial fuel cell, a bioreactor in which bacteria transform the chemical energy in biomass directly into electrical energy.

Overarching research needs in the field include bioprospecting, the search for novel microorganisms and genes that can aid in energy conversion. Research is also needed to explore the dynamics of microbial communities, enzymology, the biology of non-growing cells, modeling, genomics, nanotechnology, new microbiological techniques, and bioreactor engineering.

The report is result of a colloquium convened by the American Academy of Microbiology in March 2006. Experts in the field were brought together to discuss the status of research into various microbial energy technologies, future research needs and education and training issues in these fields.

Resources:

• Microbial Energy Conversion