Preparation of Sphaeroplasts from Lactobacillus casei by Growth with Low Concentration of Benzylpenicillin

A strain of Lactobacillus casei used for the production of a lactic acid beverage is susceptible to phage infections. Calcium ions were required for the formation of PL-i phage-infected bacteria (Watanabe & Takesue, 1972). Further studies on the role of calcium ions in phage infection required the use of protoplasts or sphaeroplasts of the host bacteria. Early trials using egg-white lysozyme, EDTA or glycine to form sphaeroplasts were unsuccessful. However, a simple procedure to produce sphaeroplasts using a low concentration of benzylpenicillin has been successfully developed and is described here together with information on some factors affecting the stability of the sphaeroplasts.