A Dual-Replicon Shuttle Vector System for Heterologous Gene Expression in a Broad Range of Gram-Positive and Gram-Negative Bacteria.

Origin of replication (ori in theta-replicating plasmids or dso in rolling circle replicating plasmids) initiates plasmid replication in a broad range of bacteria. These two kinds of plasmids were both identified in Streptococcus, a genus composed of both human commensal bacteria and pathogens with the ability to cause severe community-acquired infections, including meningitides, septicemia, and respiratory tract diseases. Given the important roles of Streptococcus in the exchange of genetic elements with other symbiotic microbes, the genotypes and phenotypes of both Streptococcus spp. and other symbiotic species could be changed during colonization of the host. Therefore, an improved plasmid system is required to study the functional, complicated, and changeable genomes of Streptococcus. In this study, a dual-replicon shuttle vector system named pDRE was constructed to achieve heterologous gene expression. The vector system contained theta replicon for Escherichia coli. The origin of rolling circle replicon was synthesized according to pMV158 in Gram-positive bacteria. By measuring the products of inserted genes at multiple cloning sites, the ability of this vector system in the replication and expression of heterologous genes was assessed in four Streptococcus and three other Gram-positive bacteria: Bacillus subtilis, Lactococcus lactis, and Staphylococcus aureus. The results showed that the newly constructed vector could simultaneously replicate and express heterologous genes in a broad range of Gram-positive and Gram-negative bacteria, thus providing a potentially powerful genetic tool for further functional analysis.