An effective strategy, applicable to Streptococcus salivarius and related bacteria, to enhance or confer electroporation competence

Despite the large number of techniques available for transformation of bact eria, certain species and strains are still resistant to introduction of fo reign DNA. Some oral streptococci are among the organisms that can be parti cularly difficult to transform. We performed a series of experiments that i nvolved manipulation of growth and recovery media and fell wall weakening, in which the electroporation conditions, cell concentration, and type and c oncentration of the transforming plasmid were varied. The variables were op timized such that a previously untransformable Streptococcus salivarius str ain,ATCC 25975, could be transformed reproducibly at a level of 10(5) trans formants per mu g of DNA. The technique was used to introduce a plasmid int o other strains of S. salivarius, including a fresh isolate. Moreover,the s ame technique was applied successfully to a wide range of oral streptococci and other gram-positive bacteria.