Fast responses of bacterial membranes to virus adsorption: a fluorescence study

After collision with their host cells, virus particles may remain mobile on cell surfaces until they become attached at firm binding sites. We propose that a virion will arrive within a typical median time at such a site, generating a membrane signal such as an increased membrane fluorescence in cells labeled with the voltage-sensitive dyes 8-anilino-1-naphthalene-sulfonate (Mg-salt) (ANS), N-phenylnaphthylamine (NPA), or 3,3'-dipentyl-2,2'-oxacarbocyanine (di-O-C5[3]). We found that the time span between virus adsorption and fluorescence response varies widely among phages and also depends on bacterial strain, metabolic state, and type of dye. di-O-C5[3]-labeled cells react within 1 sec to uncouplers such as carbonyl cyanide m-chlorophenylhydrazone (CCCP). Cells labeled with ANS and NPA react to CCCP in 4-6 sec. Bacteriophages T4, T5, chi, and BF23, added to ANS-labeled cells, change the fluorescence in 9-15 sec. T-even ghosts cause a response at identical times. Baseplate-defective phage mutant T412- and isolated adsorption organelles of smaller viruses fail to cause an effect. di-O-C5[3]-labeled cells respond to T4 at a multiplicity of infection greater than or equal to 40 within 1 sec. A longer time (8 sec) is required at lower multiplicities. The receptor-degrading phages epsilon 15, epsilon 34, c 341, and K29 need the longest time (1 min for ANS) to cause a fluorescence increase. We suggest that the delayed fluorescence response is concomitant with the surface "walk" of the virion, which is terminated at an injection site. T4 tail sheath contraction coincides with the onset of the membrane fluorescence response.