Metabolic engineering is defined as the purposeful modification of intermediary metabolism using recombinant DNA techniques. Cellular engineering, a more inclusive term, is defined as the purposeful modification of cell properties using the same techniques. Examples of cellular and metabolic engineering are divided into five categories:
 Over 100 examples of cellular and metabolic engineering are summarized. Several molecular biological, analytical chemistry, and mathematical and computational tools of relevance to cellular and metabolic engineering are reviewed. The importance of host selection and gene selection is emphasized. Finally, some future directions and emerging areas are presented.

Cellular and Metabolic Engineering An Overview

Dark, anaerobic hydrogen fermentations of starches and sugars have generally produced less than 20% of the stoichiometrically possible yield, compared to 80–90% yields in the case of ethanol and methane fermentations. Indeed, a 33% yield from glucose, with the remaining electrons secreted as acetate, is generally considered the maximum achievable hydrogen production. However, this restriction would not apply to non-growing cultures; in principle, non-growing cells could recycle much of the metabolic energy derived from the initial hydrogen/acetate fermentation into driving additional hydrogen production. Such improvements in hydrogen production may be possible using directed strategies to manipulate cellular metabolism—metabolic engineering.

Takehlro Yamamoto

Papers

Molecular Breeding of Hydrogen-evolving Bacteria