polarization values for additional bacterial species grown
under their optimal growth conditions. These values can then
be compared to values obtained from the same bacteria
species challenged with antibiotics, other toxicants and
grown under nutrient starved conditions. E. coli C600 growth
was completely inhibited in the presence of 1 Ag/ml tetracycline.
Therefore, data for this bacterium are not available.
The DPH fluorescent probe was easily incorporated into
the cytoplasmic membrane without disrupting the intact
cells and membrane. The probe does not interfere with the
event being measured, no pretreatment of cells was necessary
and a high polarization value indicates high structural
order or low membrane fluidity. The membrane polarization
values reported in this study for the five bacteria are
considered normal values for cytoplasmic membranes at
the specific temperatures and growth conditions. For example,
in other research from our laboratory, P. aeruginosa
UG2 had a membrane polarization value of 0.323, measured
at 28jC, while a Gram-negative Sphingomonas sp. UG30
exhibited a polarization value of 0.37 under optimal growth
conditions [4].