Microbial responses to solvent and alcohol stress.

Increasing fuel prices and doubts over the long-term availability of oil are currently major global concerns. Such concerns have led to national policies and objectives to develop microbially produced alcohols as fuel additives or substitutes. However, in South Africa this solution poses the further dilemma of sourcing a suitable fermentative carbohydrate that will not impact negatively on the availability of staple foods. The solution lies in the use of lignocellulosic materials, currently a waste product of the food and agriculture industries, which could be used in conjunction with a catabolically suitable production strain. In the pursuit of lignocellulosic biofuel production, conventional fermentation strains have been shown to have limited catabolic versatility. However, catabolically versatile engineered strains and novel isolates engineered with ethanologenic pathways have subsequently been shown to exhibit limitations in solvent tolerance, hindering their full potential as economically viable production strains. A considerable volume of research has been reported on the general cellular mechanisms and physiological responses to solvent shock as well as adaptive changes responsible for solvent tolerant phenotypes in mutant progeny. Here we review a number of the more common cell responses to solvents with particular focus on alcohol tolerance.