Metabolic engineering in dark fermentative hydrogen production; theory and practice

Dark fermentation is an attractive option for hydrogen production since it could use already existing reactor technology and readily available substrates without requiring a direct input of solar energy. However, a number of improvements are required before the rates and yields of such a process approach those required for a practical process. Among the options for achieving the required advances, metabolic engineering offers some powerful tools for remodeling microbes to increase product production rates and molar yields. Here we review the current metabolic engineering tool box that is available, discuss the current status of engineering efforts as applied to dark hydrogen production, and suggest areas for future improvements.

► The metabolic engineering tool box holds promise for increasing H2 production rates and yields.
► Efforts to engineer more efficient hydrogenases are reviewed.
► A variety of methods for engineering Clostridia are now available.
► Maximum H2 yields with E. coli have been achieved.
► Strategies for exceeding metabolic constraints are suggested.