Effects of a Lipophilic Environmental Pollutant (DDT) on the Phospholipid and Fatty Acid Contents of Bacillus stearothermophilus

Abstract.

Cultures of Bacillus stearothermophilus grown in a complex medium containing 1 μM DDT, exhibited longer lag adapting periods, decreased specific growth rates, and lower growth yield as compared to control cultures. The membrane lipid composition from cells grown in the presence of the insecticide was significantly different from that of control cells. The effects of DDT (2,2-bis(p-chlorophenyl)-1,1,1-trichloroethane) on growth and lipid composition of bacterial cells were also determined in cultures grown in a medium supplemented with Ca²⁺ (membrane stabilizer) to further clarify the influence of growth conditions on bacterial responses to the toxicant. The main membrane-lipid changes induced by DDT relate to a very significant increase (74%) of the relative concentration of a phosphoglycolipid, an increase of the phosphatidylethanolamine content, with a parallel decrease of phosphatidylglycerol and an unidentified phospholipid X₀. The changes of the phospholipid acyl chains relate to an increase of straight chains and a parallel decrease of branched chains. The effects of DDT-induced lipid composition alterations on membrane physical properties were monitored by fluorescence polarization studies with bacterial polar lipid dispersions. Changes in the membrane lipids upon growing the bacteria in a DDT-containing medium promoted, as expected, more ordered membranes with a shift of the phase transition temperature to higher values. Data are interpreted in the frame of an adaptation mechanism to counteract the membrane perturbation resulting from the accumulation of the insecticide molecules in the lipid bilayer.