MECHANISMS OF RESISTANCE OF WHOLE CELLS TO TOXIC ORGANIC-SOLVENTS

Many processes in modern biotechnology, particularly biotransformations and environmental bioremediation, are hindered by the toxic effects of organic solvents on whole cells. These compounds dissolve in the cell membrane, disturbing its integrity and effecting specific permeabilization. The hydrophobicity of a compound, expressed as its log P value, is a good indicator of toxicity. Substances with a log P value in the range 1-5 are, in general, toxic to whole cells. However, in recent years, there have been several reports of bacteria exhibiting resistance to toxic solvents. The main adaptative reactions are alterations in the composition of the membrane, particularly changes in fatty-acid composition, phospholipid headgroups, and in the protein content. One of the key processes in the adaptation of some Pseudomonas strains, enabling them to tolerate organic solvents appears to be the isomerization of cis- into trans-unsaturated fatty acids. A greater understanding of these adaptations should eventually allow biotransformation reactions to be carried out in inhospitable two-phase systems incorporating an organic phase.