To truly distinguish whether a streptomycin-resistant mutant is introduced by transformation
via electroporation or generated by spontaneous mutation, we created two silent mutations flanking the missense mutation of codon 43 of rpsL-SR1 (Fig. 1). PCR amplicon was generated from this mutation, named rpsL-WM, and used to transform V. parvula PK1910. Obeticholic Acid chemical structure In five independent experiments, we obtained similar results: when equal amounts of DNA was used, rpsL-WM transformation always gave two to three times more streptomycin-resistant colonies than rpsL-WT transformation. The result of one transformation was shown in Fig. 2a. The rpsL gene from all these streptomycin-resistant colonies was then sequenced. Of the 19 colonies from rpsL-WM transformation, 11 contained the rpsL-WM sequence (Fig. 2b), three had the rpsL-SR1 sequence, and five had the rpsL-SR2 sequence. In contrast, of the nine colonies from the rpsL-WT transformation, five had the rpsL-SR1 sequence, four had the rpsL-SR2, and no colony had the rpsL-WM sequence. This result unequivocally demonstrates that V. parvula PK1910 is transformable. Veillonellae bacteria have so far remained as one of the most prevalent yet least studied microorganisms
in the human oral microbiome, largely due to our inability to genetically transform them. In this study, we set forth to test the transformability of Dinaciclib V. parvula strain PK1910, inspired by the finding of multiple competence-related genes on its genome. To this end, we have generated a ‘watermarked’rpsL gene conferring streptomycin resistance and shown that V. parvula PK1910 is transformable by electroporation. To our knowledge, this is the first report of genetic transformation in veillonellae. Electroporation has been successfully
used for DNA transformation in a large number of bacteria, such as Lactococcus lactis, Clostridium perfringens, Propionibacterium acnes, and Fusobacterium nucleatum, with varying optimal conditions for each bacterium (McIntyre & Harlander, 1989; Jiraskova et al., 2005; Kinder Haake et al., 2006; Cheong et al., 2008). In our efforts to optimize the procedure for transformation, we identified several parameters important to V. parvula transformation. First, the culturing media and Phosphatidylinositol diacylglycerol-lyase cell growth stage are important. Veillonella parvula could be reproducibly transformed only when cells were grown in ASSPL medium and harvested at the early exponential phase. Another parameter important to transformation is MgCl2 in the electroporation buffer. The incorporation of 1 mM MgCl2 in the electroporation buffer is required for the success of transformation. The pulse length and voltage of electroporation are also important. Success was repeatedly achieved with field strength of 20 kV cm−1, capacitance of 25 μF, and resistance setting of 200 Ω. Because our goal in this study was to examine the possibility of using electroporation to introduce DNA into V.