Mutanolysin-induced spheroplasts of Streptococcus mutans are true protoplasts

Abstract

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.