Glass bead transformation method for gram-positive bacteria:-
A simple, inexpensive and reproducible transformation method was developed for Gram-positive bacteria. It was based on agitation of bacterial protoplasts with glass beads in the presence of DNA and polyethylene glycol. By using this method, introduction of pGK12 into protoplasts of several strains of Gram-positive bacteria was achieved.
Braz J Microbiol. 2009 Oct-Dec; 40(4): 923–926.
Published online 2009 Dec 1. doi: 10.1590/S1517-838220090004000025
Methods for making protoplasts from gram-positive bacteria will not work for gram-negatives. Look for papers that describe preparation of spheroplasts. The details will be different from one bacterial species to another. Here is a classic that you can get free from Pubmed Central: Schnaitman, C.A., 1970. Protein composition of the cell wall and cytoplasmic membrane of Escherichia coli. J. Bacteriol. 104, 890–901. PMID: 4099097 PMCID: PMC285073.