Molecular Sieving by theBacillus megateriumCell Wall and Protoplast

Abstract

Passive permeabilities of the cell wall and protoplast of Bacillus megaterium strain KM were characterized by use of 50 hydrophilic probing molecules (tritiated water, sugars, dextrans, glycols, and polyglycols) which varied widely in size. Weight per cent uptake values (RW) were measured at diffusional equilibrium under conditions that negated the influences of adsorption or active transport. Plots of Rw for intact cells as a function of number-average molecular weight (Ma) or Einstein-Stokes hydrodynamic radius (iES) of the solutes showed three phases: a protoplast uptake phase with a polydisperse exclusion threshold of M1, = 0.6 x 103 to 1.1 x 103, tES = 0.6 to 1.1 nm; a cell wall uptake phase with a polydisperse exclusion threshold of MR = 0.7 x 105 to 1.2 x 105, rES 8.3 nm; and a total exclusion phase. Isolated cell walls showed only the latter two phases. However, it became evident that the cell wall selectively passed only the smallest molecules in a heterodisperse polymer sample. When the molecular-weight distributions of polyglycol samples (M1, = 1,000, 1,450, and 3,350) were determined by analytical gel chromatography before and after uptake by intact cells or isolated cell walls, a quasi-monodisperse exclusion threshold was obtained corresponding to M" = 1,200, rEs = 1.1 nm. The permeability of isolated protoplasts was assessed by the relative ability of solutes to effect osmotic stabilization. An indefinite exclusion threshold, evident even with monodisperse sugars, was attributed to lengthwise orientation of the penetrating rod-shaped molecules. Altogether, the best estimate of the limiting equivalent porosity of the protoplast was 0.4 to 0.6 nm in radius and of the cell wall, 1.1 nm.

Characterization of translocation pores inserted into plasma membranes by type III-secreted Esp proteins of enteropathogenic Escherichia coli

“…2A, significant osmoprotection was observed with PEG 3000 and PEG 6000 or with dextrans exceeding 6000 Da. Based on the average Einstein±Stokes molecular diffusion radii reported by Scherrer and Gerhardt (1971), the experiments indicate a minimal pore diameter of Esp-inserted pores in erythrocyte membranes of 3±5 nm. As shown in the experiment with bacterial cultures, molecules larger than PEG 2000 or dextran 6000 yielded significant protection against CM-mediated haemolysis (Fig.…”

“…Osmoprotection with sucrose, PEGs and dextrans exhibiting increasing Einstein±Stokes diffusion radii ranging from 0.47 nm (sucrose) to 3.5 nm (dextran 20) (Scherrer and Gerhardt, 1971) indicated a minimal diameter of the pore between 3 and 5 nm (Fig. 2).…”

Caspase-1 dependent macrophage death induced by Burkholderia pseudomallei

“…THP-1 cells were infected with B. pseudomallei in the presence of 30 mM of various PEGs. PEGs used were PEG 200 [Hydrodynamic radius (Hr) = 0.56 nm], 1000 (Hr = 1 nm), 2000 (Hr = 1.22 nm), 3000 (Hr = 1.44 nm) and 4000 (Hr = 1.92 nm) (Scherrer and Gerhardt, 1971). Sucrose (Sigma) was included as control.…”

Assembly mechanism of the oligomeric streptolysin O pore: the early membrane lesion is lined by a free edge of the lipid membrane and is extended gradually during oligomerization

“…wt 4 kDa) or dextran 60 (60 kDa). The effective diameter of dextran 4 in solution is estimated to be 3 nm and that of dextran 60 to be 10 nm (Scherrer and Gerhardt, 1971). The cells were exposed to C530A toxin with or without T250C-AEDANS, and the time course of cell lysis was followed by measuring the decrease in turbidity of the cell suspension.…”