The energy dependence of detergent resistance in Enterobacter cloacae: a likely requirement for ATP rather than a proton gradient or a membrane potential

Abstract

The enteric bacterium Enterobacter cloacae was grown both aerobically and anaerobically in the presence of up to 1% of the anionic detergent sodium dodecyl sulfate (SDS). A continuous energy supply was necessary to maintain cell integrity and cells grown in SDS (0.1–1%) lysed during carbon-limited stationary phase. The respiratory inhibitor KCN (3 mM) caused rapid lysis when added to aerobic, log phase, SDS-containing cultures growing on glucose as the carbon source. However, when the SDS (0.5%) was added 30 min after KCN, lysis did not occur. The likely reason for this discrepancy concerns the cellular ATP levels. In aerobic cells the ATP levels dropped 10- to 15-fold within 1 min of adding KCN and then increased gradually over the next 30 min. Similarly, the addition of 2 mM iodoacetic acid, an inhibitor of glycolysis, to anaerobic, log phase, SDS-containing cultures caused rapid lysis. However, unlike the situation for KCN-treated aerobic cells, lysis still occurred when SDS (0.5%) was added 30 min after addition of iodoacetic acid. The reason for this difference is that in anaerobic cells, ATP levels dropped 10-to 12-fold within 5 min of the addition of iodoacetic acid and then did not increase over the next 30 min. Evidence that the energy requirement was for ATP was provided by uptake experiments with [14C]benzoic acid and α-[14C] isoaminobutyric acid that showed that the proton gradient (ΔpH) and the membrane potential (Δψ were the same in cells grown in the presence or absence of SDS. Likewise, for both aerobic and anaerobic cultures the absence of a proton gradient (ΔpH = 0) did not cause cell lysis. In carbon-starved stationary phase cells, Δψ was the same in the presence and absence of SDS. Taken together, this evidence suggests that ATP, and not ΔpH or Δψ, is required for SDS resistance.Key words: sodium dodecyl sulfate, bacterial detergent resistance, energy-dependent cell lysis, membrane potential, proton gradient, ATP.