Thermophilic ethanologenesis: future prospects for second-generation bioethanol production

Strategies for improving fermentative ethanol production have focused almost exclusively on the development of processes based on the utilization of the carbohydrate fraction of lignocellulosic material. These so-called 'second-generation' technologies require metabolically engineered production strains that possess a high degree of catabolic versatility and are homoethanologenic. It has been suggested that the production of ethanol at higher temperatures would facilitate process design, and as a result the engineered progeny of Geobacillus thermoglucosidasius, Thermoanerobacterium saccharolyticum and Thermoanerobacter mathranii now form the platform technology of several new biotechnology companies. This review highlights the milestones in the development of these production strains, with particular focus on the development of reliable methods for cell competency, gene deletion or upregulation.