Binding of lipophilic anions to microbial cells

We have studied the binding of lipophilic anions (LPAs) to bacterial and yeast cells, E. coli-derived membrane vesicles and pure phospholipid vesicles and membrane-containing bacteriophage particles. The inactivation of the cells by heat or phenol treatment leads to a sixfold to eightfold increase in the binding of phenyldicarbaundecaborane (PCB-). However, heating has a small effect on the strong binding of this anion to membrane vesicles and membrane-containing phage particles, Similar to PCB-, the intact cells bind small amounts of naphthyldicarbaundecaborane (NCB-) and tetraphenylboron (TPB-), However, the cells bind 6-15-fold larger amounts of diphenyldicarbaundecaborane (DPCB-) and decyldicarbaundecaborane (DCB-) than PCB-. The binding of DCB- and DPCB- to membrane-containing phage particles, pure lipid vesicles and a stabilized emulsion of olive oil is also stronger relative to the binding of PCB-. The results obtained with the polycationic antibiotic Polymyxin B (PMB) and bacterial viruses suggest that the smaller amount of binding of LPAs to intact cells is at least partially due to the difficult partitioning into the interior of phospholipid bilayers, PMB produces a tenfold increase in PCB- binding to intact E. coli cells. It also increases PCB- binding to heat-inactivated cells (about 15%) and to envelope-containing viruses (up to 60%). This indicates the presence of an intrinsic barrier for LPA binding to membranes. Screening of the cell surface charge by high concentrations of salts affects the binding of LPAs rather weakly, but the amount of bound LPAs increases considerably when the medium is below pH 4. (C) 1997 Elsevier Science S.A.