A HOST-VECTOR SYSTEM FOR HETEROLOGOUS GENE-EXPRESSION IN STREPTOCOCCUS-GORDONII

We have developed a host-vector system for heterologous gene expressio n in Streptococcus gordonii (Sg) Challis (formerly Streptococcus sangu is), a commensal bacterium of the human oral cavity. The system is bas ed on (i) integration of plasmid insertion vectors into the chromosome of specially engineered recipient hosts, and (ii) the use of the M6-p rotein-encoding gene (emm6) as a partner for construction of translati onal gene fusions. M6 is a streptococcal surface protein already prove n useful as a fusion partner for the delivery of foreign antigens to t he surface of Sg [Pozzi et al., Infect. Immun. 60 (1992) 1902-1907]. I nsertion vectors carry a drug-resistance marker, different portions of emm6 and a multiple cloning site to allow construction of a variety o f emm6-based fusions. Upon transformation of a recipient host with an insertion vector, 100% of transformants acquire both the drug-resistan ce marker and the capacity of displaying the M6 molecule on the cell s urface. Chromosomal integration occurred at high frequency in recipien t host GP1221. Transformation with 1 mu g of insertion vector DNA yiel ded 8.1 x 10(5) transformants per ml of competent cells.