Characterization of the mechanisms of adaptation of Mycobacterium to organic solvents

Cells of Mycobacterium vaccae were grown in toluene, ethanol, methyl tert-butyl ether (MTBE) and glycerol, exhibiting different degrees of tolerance towards these compounds, and being able to use both ethanol and glycerol as sole carbon and energy sources. Cellular adaptation to ethanol and MTBE led to significant changes in the membrane fatty acid (FA) composition, by modifications in the proportion of straight-chain saturated, monounsaturated, branched-chain saturated and 10-methyl FA. Ethanol-adapted cells had a different morphology than MTBE-adapted cells: regular rod-shaped cells were observed with MTBE but cell shrinkage occurred in the presence of ethanol. Besides, cells in the presence of ethanol formed aggregates. The zeta potential of cells was -49.3 mV before the addition of solvent, becoming less negative after MTBE adaptation (-33.1 mV) and more negative in ethanol-adapted cells (-45.9 mV). After adaptation to these solvents, cells acquired an improved tolerance towards efflux pump inhibitors (EPIs), but became more susceptible to antibiotics.