Engineering Cyanobacteria for Efficient Photosynthetic Production: Ethanol Case Study

Cyanobacterial photosynthetic production of ethanol directly utilizing carbon dioxide and solar energy provides a potential sustainable route for green biofuels. Ethanol production is one of the most developed systems for industrial cyanobacteria "cell factories" and provides a model for studying advanced metabolic engineering strategies. Although trace contents of ethanol could be detected in fermentation products of several cyanobacteria strains, ethanol is not a natural metabolite for a majority of cyanobacteria species. Introduction of an optimized metabolic pathway consisting of just two enzymes, pyruvate decarboxylase and type II alcohol dehydrogenase, successfully converted several cyanobacteria strains, including model and nonconventional strains, into ethanolgenic cell factories. Adopting systematic optimization strategies targeting on enzymes, pathways, cells, and processes, efficient cyanobacteria cell factories for ethanol production have been developed, yielding the highest titer, strongest productivities, and highest carbon partitioning ratio of the final products among the current cyanobacterial photosynthetic production technologies. This chapter reviews the development history and recent progress on engineering cyanobacteria for ethanol production. Achievements in pathway optimization, chassis selection, and development of metabolic engineering strategies are highlighted and discussed to inspire the future directions of this technology.