Biochemical changes in bifidobacterium bifidum var. Pennsylvanicus after cell wall inhibition

The cytoplasmic membrane is a primary target for the staphylocidal action of thrombin-induced platelet microbicidal protein

Thrombin-induced platelet microbicidal protein (tPMP-1) is a small, cationic peptide released from rabbit platelets exposed to thrombin in vitro. tPMP-1 is microbicidal against a broad spectrum of bloodstream pathogens, including Staphylococcus aureus. Preliminary evidence suggests that tPMP-1 targets and disrupts the staphylococcal cytoplasmic membrane. However, it is not clear if the cytoplasmic membrane is a direct or indirect target of tPMP-1. Therefore, we assessed the in vitro activity of tPMP-1 versus protoplasts prepared from logarithmic-phase (LOG) or stationary-phase (STAT) cells of the genetically related S. aureus strains 19S and 19R (tPMP-1 susceptible and resistant, respectively). Protoplasts exposed to tPMP-1 (2 microg/ml) for 2 h at 37 degrees C were monitored for lysis (decrease in optical density at 420 nm) and ultrastructural alterations (by transmission electron microscopy [TEM]). Exposure to tPMP-1 resulted in substantial lysis of LOG but not STAT protoplasts of 19S, coinciding with protoplast membrane disruption observed by TEM. Thus, it appears that tPMP-1-induced membrane damage is influenced by the bacterial growth phase but is independent of the staphylococcal cell wall. In contrast to 19S, neither LOG nor STAT protoplasts of 19R were lysed by tPMP-1. tPMP-1-induced membrane damage was further characterized with anionic planar lipid bilayers subjected to various trans-negative voltages. tPMP-1 increased conductance across bilayers at -90 mV but not at -30 mV. Once initiated, a reduction in voltage from -90 to -30 mV diminished conductance magnitude but did not eliminate tPMP-1-mediated membrane permeabilization. Therefore, tPMP-1 appears to directly target the staphylococcal cytoplasmic membrane as a primary event in its mechanism of action. Specifically, tPMP-1 likely leads to staphylococcal death, at least in part by permeabilizing the bacterial membrane in a voltage-dependent manner.

Effects of growth conditions on the lipid composition of Bifidobacterium bifidum subsp. pennsylvanicum

Lipid-phosphorus and lipid-galactose content and phospholipid and fatty acid composition of Bifidobacterium bifidum subsp. pennsylvanicum were examined under a wide variety of growth conditions. Cells from 29-C cultures contained less lipid-phosphorus than did cells from 37-C cultures, but their lipid-galactose content and phospholipid composition did not differ. At both temperatures, the growth phase influenced the lipid composition similarly. Phosphate, Mg2+ and K+ concentrations in the medium did neither significantly change the cellular lipid-phosphorus content nor the phospholipid composition. Only Mg2+-deficiency markedly reduced growth and lowered the content of cellular lipid-galactose. Omission of Tween 80 from the medium did not affect growth, but lowered the content of lipid-galactose and augmented those of lipid-phosphorus and diphosphatidylglycerol in the cell. Increased osmolarity and substitution of other Tween for Tween 80 caused the same changes in lipid composition, and besides inhibited growth. Omitting Tween 80 and replacing it by other Tweens dramatically reduced the percentage of unsaturated fatty acids. C12- and C14-fatty acids made up about 50% of total fatty acids in cells from Tween 20 cultures and 12-14% in cells from Tween 40 and Tween 60 cultures. The differences in the decline of unsaturated fatty acids and in the degree of replacement of these acids by C12- and C14-fatty acids may be related to the variations in growth in cultures with various Tweens by way of changes in the physical state of the membrane lipids.

Effects of growth conditions on the ion composition of Bifidobacterium bifidum subsp. pennsylvanicum

The cation content of Bifidobacterium bifidum subsp. pennsylvanicum was markedly influenced by the washing procedure of the cells, by the growth phase and the temperature, and by the composition of the culture medium. Optimal retention of cations was achieved by washing with 0.25 M MgCl2 at 20C. The intracellular Na+ concentration rose during growth in normal medium to a constant value in the stationary phase, the K+ concentration rose in the exponential phase, but fell in the stationary phase. Cells from 29-C cultures contained more Na+ and less K+ in the stationary phase than did cells from 37-C cultures, but the total cation content was the same at 29 and 37C. Intracellular Na+ and K+ concentrations were dependent on the concentrations in the medium and on its osmolarity. The intracellular Na+/K+ ratio varied from 0.04 to 2.3. The concentrations of Na+,K+ and phosphate in the medium hardly affected growth. Mg2+-deficiency of the medium markedly decreased the concentration of Mg2+ within the cell; its concentration in the cell sap was greatly affected, but the amount of sedimentable, bound Mg2+ only slightly. The content of K+ within the cell decreased in Mg2+-deficient medium, but the concentration of Na+ did not. Omission of Tween 80 as well as its substitution by Tween 20 caused a decrease of intracellular K+. Cells from Tween 40 and Tween 60 cultures additionally contained markedly less Na+.

Biochemical changes in Bifidobacterium bifidum var. pennsylvanicus after cell wall inhibition. IX. Metabolism and release of cellular lipids in the presence of antibiotics

Inhibiton of cell wall synthesis caused simultaneously an increase in cellular phospho-and glycolipids and a marked release of these compounds to the medium. The composition of the cellular and the released glyco-and phospholipids was almost the same. Antibiotics, which inhibit cell wall synthesis, did not influence glycolipid composition, but increased the relative and absolute amounts of disphosphatidylglycerol and its lysoderivatives. Incorporation and chase experiments demonstrated a considerable stimulation of phospholipid metabolism, and of diphosphatidylglycerol synthesis especially. Release of lipids was not accompanied by loss of cellular protein. Omission of Tween 80 from the medium decreased the release by about 50% and increased the relative amounts of the phosphogalactolipids in the cells and in the culture fluid. Inhibitors of protein synthesis and valinomycin caused a decrease in cellular lipidphosphorus content, and a relative increase of the phosphogalactolipids. No release of lipids was observed under these conditions.