Mm. Donato et al., BACILLUS-STEAROTHERMOPHILUS AS A MODEL TO EVALUATE MEMBRANE TOXICITY OF A LIPOPHILIC ENVIRONMENTAL-POLLUTANT (DDT), Archives of environmental contamination and toxicology, 33(2), 1997, pp. 109-116
The thermophilic eubacterium Bacillus stearothermophilus has been used
as a model system to identify DDT-promoted events in biological membr
anes putatively related with the insecticide toxicity. Two strategies
have been approached: a) bacterial growth and viability were followed
and the effects of DDT (2,2-bis(p-chlorophenyl)-1,1,1-trichloroethane)
determined; b) biophysical studies with fluorescent probes were perfo
rmed to elucidate the effects of DDT on the organization of the membra
ne lipid bilayer. The effects of DDT on growth and physical properties
of the membrane were also determined in the presence of Ca2+ to furth
er identify the interference of the insecticide at the membrane level
and its putative contribution to cell toxicity. Growth inhibition by D
DT is concentration-dependent, being attenuated or removed by the addi
tion of 2.5-mM Ca2+ to bacterial cultures. Consistently, fluorescence
polarization of 1,6-diphenyl-1,3,5-hexatriene (DPH) and its propionic
acid derivative (DPH-PA) exhibited opposite effects of Ca2+ and DDT on
the physical state of bacterial polar lipid dispersions. Growth and v
iability of bacterial cells are affected by DDT concentrations lower t
han those able to induce detectable bulk fluidity alterations, indicat
ing high sensitivity of the intact bacterial system to alterations in
limited membrane domains not directly probed by fluorescent probes tha
t only report the average behavior of membrane lipid population.