Determination of Gardnerella vaginalis genome size by pulsed-field gel electrophoresis.

The chromosomal DNA of four strains of Gardnerella vaginalis were digested with rare cutting restriction enzymes and analyzed by pulsed-field gel electrophoresis (PFGE). The four strains studied were two clinical isolates (GVP 004 & GVP 007) and two American Type Culture Collection strains (ATCC 14018 & ATCC 14019). The restriction enzyme SfiI generated two DNA fragments of about 0.6 Mb and 1.1 Mb in all four strains giving a G. vaginalis genome size of about 1.7 Mb. A similar genome size was calculated utilizing two more GC-rich sequence specific restriction endonucleases, NotI and AscI. When digested with AscI, the chromosomal DNA of all four strains gave rise to 11 to 12 DNA fragments ranging between 0.01 Mb to 0.43 Mb. DNA from the two clinical isolates were digested by NotI (yielding 7 to 9 fragments), while the DNA from the two ATCC strains were resistant to NotI digestion. In contrast the clinical isolates, DNA from the two ATCC strains gave an identical profile for all restriction endonucleases tested. From double digestion experiments, the two SfiI sites could be localized on two AscI fragments. From these PFGE studies, it is concluded that the G. vaginalis genome is a circular DNA that ranges between 1.67 Mb and 1.72 Mb in size.