BINDING OF LIPOPHILIC ANIONS TO MICROBIAL-CELLS

We have studied the binding of lipophilic anions (LPAs) to bacterial a nd yeast cells, E. coli-derived membrane vesicles and pure phospholipi d vesicles and membrane-containing bacteriophage particles. The inacti vation 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 ani on to membrane vesicles and membrane-containing phage particles, Simil ar to PCB-, the intact cells bind small amounts of naphthyldicarbaunde caborane (NCB-) and tetraphenylboron (TPB-), However, the cells bind 6 -15-fold larger amounts of diphenyldicarbaundecaborane (DPCB-) and dec yldicarbaundecaborane (DCB-) than PCB-. The binding of DCB- and DPCB- to membrane-containing phage particles, pure lipid vesicles and a stab ilized emulsion of olive oil is also stronger relative to the binding of PCB-. The results obtained with the polycationic antibiotic Polymyx in B (PMB) and bacterial viruses suggest that the smaller amount of bi nding of LPAs to intact cells is at least partially due to the difficu lt partitioning into the interior of phospholipid bilayers, PMB produc es a tenfold increase in PCB- binding to intact E. coli cells. It also increases PCB- binding to heat-inactivated cells (about 15%) and to e nvelope-containing viruses (up to 60%). This indicates the presence of an intrinsic barrier for LPA binding to membranes. Screening of the c ell surface charge by high concentrations of salts affects the binding of LPAs rather weakly, but the amount of bound LPAs increases conside rably when the medium is below pH 4. (C) 1997 Elsevier Science S.A.