Preparation of protoplasts of group H streptococci (Streptococcus sanguis)

Streptococcus pneumoniae proteins released into medium upon inhibition of cell wall biosynthesis

Inhibition of murein biosynthesis in Streptococcus pneumoniae by either penicillin or bacitracin leads to an increase in the amount of protein secreted into the medium. This process was studied in wild-type cells grown under lysis-permissive conditions as well as in an autolysin-deficient mutant. The time course of secretion did not follow cellular lysis but commenced immediately after the addition of the cell wall inhibitor in a manner similar to that described recently for cell wall and membrane components in various tolerant streptococci. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis showed that this increase was not due to the stimulation of release of three protein components which are secreted under normal growth conditions; rather, a complex set of cellular proteins escaped from the antibiotic-treated pneumococci. The proteins released during bacitracin treatment was slightly different from those observed when penicillin was used. Analysis on sucrose gradients indicated that the secreted proteins were membrane bound rather than soluble. Membrane vesicles could indeed be detected by electron microscopy of negative-stained secreted material.

Mutanolysin-induced spheroplasts of Streptococcus mutants are true protoplasts

A method is described for the preparation of protoplasts of Streptococcus mutans BHT. The muralytic enzyme mutanolysin was prepared free of contaminating proteinases and shown to completely dissolve cell walls of this strain. Whole cells were converted to stabilizable protoplasts by using the enzyme in an isotonic medium containing 40% raffinose. Experiments using [3H]thymidine and [14C]leucine as cytoplasmic pool markers revealed only minimal (10%) leakage during a 1-h incubation. Examination by electron microscopy revealed the apparent absence of structural cell wall on the enlarged spherical bodies. Quantitative chemical analyses of membranes prepared by lysing protoplasts demonstrated only very small amounts of rhamnose and trace amounts of galactose. These sugars are the principal components of the BHT cell wall polysaccharide. Also, there were only small amounts of peptidoglycan components (e.g., N-acetylglucosamine) in the purified membranes obtained by this method.

Membrane and cytoplasmic location of streptolysin S precursor

Group A streptococci which produce streptolysin S (SLS) contain a cellular potential hemolysin (CPH) which is precursor to extracellular SLS. Since the cellular location of CPH is unknown, protoplasts prepared with group C phage-associated lysin or mutanolysin from 18 strains of group A streptococci were fractionated into subcellular components and assayed for CPH. In all strains, most of the CPH was membrane associated, and most could not be removed from membranes by washing with buffer or 2 M LiCl. CPH remaining in the cytoplasmic fraction was sedimentable, but not associated with membrane fragments. Ribonuclease digestion neither solubilized nor inactivated CPH from membranes. Streptococcal proteinase also did not affect CPH, although it did inactivate SLS. We conclude that group A streptococci contain a major pool of CPH in the membrane and a smaller pool in the cytoplasm.

Lysis and protoplast formation of group B streptococci by mutanolysin

Group B streptococci, refractory to previously tested muralysins under physiological conditions, were successfully converted to protoplasts by use of a recently describede N-acetyl muramidase, mutanolysin, derived from a streptomycete. Purified enzyme was effective, but crude preparations, although degrading cell walls, simultaneously produced peculiar effects of cytoplasmic coagulation, retention of cell shape, loss of some intracellular enzymes, and a rise in optical density. Addition of purified mutanolysin to the array of muralysins (group C streptococcal phage-associated lysin, lysozyme), previously successful in preparing protoplasts of different streptococci, now makes possible enzymatic preparation of protoplasts of streptococci of groups A, B, C. D. G, and H.

Lethal effect of a heterologous murein hydrolase on penicillin-treated Streptococcus sanguis

Nine strains of Streptococcus sanguis exhibited tolerance to benzylpenicillin: the growth of each strain was susceptible to penicillin with minimal inhibitory concentrations of 0.1 mug/ml or lower, but the bacteriolytic and bactericidal effects were limited in each case. The tolerance of these bacteria was also reflected in the large discrepancies between the minimal inhibitory and minimal bactericidal concentrations for benzylpenicillin. The hypothesis that a natural deficiency of endogenous murein hydrolase (autolysin) in this species accounts for the penicillin tolerance was tested by using a heterologous murein hydrolase, the C-phage-associated lysin. In seven of the strains, addition of the lysin to the culture together with penicillin or other cell wall inhibitors resulted in lysis and rapid loss of viability. The enzyme alone did not appreciably affect normally growing cultures. The irreversible effects of penicillin plus lysin were drastically reduced in the presence of the bacteriostatic agents chloramphenicol and cerulenin. Speculations based on experiments are presented for the mechanisms by which penicillin treatment sensitizes these bacteria to an exogenous lytic enzyme. Similar phenomena requiring cooperation of host factors and penicillin may occur during infection, since somewhat similar although less pronounced results were obtained by addition of human lysozyme to penicillin-treated S. sanguis.

Cellular location of streptolysin O

Streptolysin O was measured in subcellular fractions of group A streptococci obtained after preparation of protoplasts in a hypertonic buffer containing raffinose. Most of the activity was located in the periplasm (the region between cell wall and membrane) and did not differ in several characteristics from that of extracellular streptolysin O. Of the enzymes used as subcellular markers, aldolase and maltase (cytoplasmic) and acid phosphatase (membrane associated) were in the same fractions as found in other bacteria. However, the location of alkaline phosphatase differed from that of other bacteria in the most of the activity was in cytoplasm rather than in the periplasm.