Natural transformation of Streptococcus crista

Abstract

Over the years Streptococcus gordonii (sanguis) Challis has become the workhorse of genetic manipulations for the sanguis group of oral streptococci. This is because strain Challis was shown in early studies to be highly naturally competent for transformation. However, Challis is not usually the most appropriate strain to use in studies which focus on oral microbial adherence. We report that other members of the newly reorganized sanguis group, particularly within the species S. crista, display reasonable transformation frequencies, with both plasmid and chromosomal DNA, if transformed at the appropriate time during the growth curve. The ability to transform S. crista may be especially important for genetic studies of biological properties that appear to be limited to these specific streptococcal strains.

Fig. 1

Transformation of strains of S. crista. The bacteria were grown as described in the text and, at 45-min intervals, a portion of the culture was mixed with 1 μg of pDL278 DNA. The mixture was incubated and plated on medium containing spectinomycin. Colony forming units (CFU) are shown as a line graph and the bars represent the number of spectinomycin-resistant transformants/ml obtained at each sampling.

Fig. 2

Transformation of strains of S. crista and S sanguis. Experimental conditions were the same as described in the legend to Fig. 1.

Fig. 3

Southern blot showing the presence of pDL278 in transformed strains of S. crista. Total DNA was obtained from each transformed strain of S. crista, digested with EcoRI and a Southern blot was prepared. pDL278 DNA (6.6 kb), labeled with 32P, was used as the hybridization probe. The lane marked (–)CON contained total DNA from wild-type strain CC5A.

Fig. 4

Transformation of strains of S. gordonii and S. oralis. Experimental conditions were the same as described in the legend to Fig. 1.