Recent advances in genetic engineering of thermophilic ethanol producing bacteria

Abstract

Thermophilic bacteria have gained increased interest as bioprocessing platforms for bioethanol production from second generation biomass with a particular emphasis on thermophilic clostridia species. Although thermophilic bacteria possess many advantages such as broad substrate spectra, fast growth rates, and high tolerance for environmental factors, they usually tolerate less ethanol than yeasts and produce various by-products apart from ethanol. These two factors have been addressed for several thermophilic bacteria through genetic engineering, to increase ethanol tolerance or cut off branching fermentation pathways and direct end product formation towards ethanol only. The best wild type ethanol producers belong to clostridia, particularly Thermoanaerobacter, Thermoanaerobacterium, and Clostridium. Additionally, non-native ethanol producers exhibiting cellulolytic properties have been genetically modified to insert genes for ethanol production pathways, as of Caldicellulosiruptor bescii. The scope of this chapter is on recent genetic engineering of thermophilic ethanol-producing bacteria.