MECHANISMS FOR SOLVENT TOLERANCE ILL BACTERIA

The development of tolerance in Pseudomonas putida DOT-T1 to toluene a nd related highly toxic compounds involves short- and long-term respon ses, The short-term response is based on an increase in the rigidity o f the cell membrane by rapid transformation of the fatty acid cis-9,10 -methylene hexadecanoic acid (C17:cyclopropane) to unsaturated 9-cis-h exadecenoic acid (C16:1,9 cis) and subsequent transformation to the tr ans isomer. The long-term response involves in addition to the changes in fatty acids, alterations in the level of the phospholipid polar he ad groups: cardiolipin increases and phosphatidylethanolamine decrease s. The two alterations lead to increased cell membrane rigidity and sh ould be regarded as physical mechanisms that prevent solvent penetranc e. Biochemical mechanisms that decrease the concentration of toluene i n the cell membrane also take place and involve: (i) a solvent exclusi on system and (ii) metabolic removal of toluene via oxidation. Mutants unable to carry out cis --> trans isomerization of unsaturated lipids , that exhibit altered cell envelopes because of the lack of the OprL protein, or that are unable to exclude toluene from cell membranes are hypersensitive to toluene.