Abstract
The six Veillonella species found in the human oral cavity are among the most abundant members of the oral flora, occurring in both supra- and subgingival dental plaque as well as on the oral mucosa. Epidemiological data have also implicated these species in the development of the most common oral diseases. Despite their ubiquity, abundance, and ecological significance, surprisingly little is known about Veillonella biology, largely due to the difficulties associated with their genetic manipulation. In an effort to improve genetic analyses of Veillonella species, we isolated a collection of veillonellae from clinical plaque samples and screened for natural competence using a newly developed transformation protocol. Numerous strains of V. parvula were found to exhibit a natural competence ability that was highly influenced by growth medium composition. By exploiting this ability, we were able to utilize cloning-independent allelic exchange mutagenesis to identify the likely source of DNA uptake machinery within a locus homologous to type II secretion systems (T2SS). Interestingly, V. parvula natural competence was found to exhibit a clear hierarchy of preference for different sources of DNA (plasmid < PCR product < genomic DNA), which is unlike most naturally competent species. Genomic comparisons with other members of the Veillonellaceae family suggest that natural competence is likely to be widely distributed within this group. To the best of our knowledge, this study is the first demonstration of natural competence and targeted allelic exchange mutagenesis within the entire Veillonellaceae family and demonstrates a simple and rapid method to study Veillonella genetics.
Highlights
Of the 13 species in the genus Veillonella (Aujoulat et al, 2014), six are typically found in the oral cavities of humans (V. atypica, V. dispar, V. parvula, V. denticariosi, V. rogosae, and V. tobetsuensis), where they comprise significant fractions of the oral flora found within supra- and subgingival dental plaque as well as on the oral mucosa (Aas et al, 2005; Beighton et al, 2008; Haffajee et al, 2009; Zaura et al, 2009; Abusleme et al, 2013)
Since it was already established that allelic exchange mutagenesis is ineffective via electrotransformation of OK5, we were curious whether veillonellae might be naturally transformable, and likely amenable to allelic exchange mutagenesis
Veillonella was considered to be a genetically intractable genus, as attempts to transform different veillonellae were unsuccessful. This changed several years ago when it was demonstrated that electrotransformation was possible in V. atypica strain OK5 (Liu et al, 2012), which was soon followed by reports of targeted mutagenesis in this strain (Zhou et al, 2015a,b, 2016)
Summary
Of the 13 species in the genus Veillonella (Aujoulat et al, 2014), six are typically found in the oral cavities of humans (V. atypica, V. dispar, V. parvula, V. denticariosi, V. rogosae, and V. tobetsuensis), where they comprise significant fractions of the oral flora found within supra- and subgingival dental plaque as well as on the oral mucosa (Aas et al, 2005; Beighton et al, 2008; Haffajee et al, 2009; Zaura et al, 2009; Abusleme et al, 2013). Many fastidious periodontal pathogens have an obligate growth requirement for heme, which can be provided by the veillonellae through de novo synthesis (Zhou et al, 2016). This and the various other unusual aspects of Veillonella metabolism are presumably of particular importance to support the persistence of periodontopathogens before the onset of oral inflammatory disease (i.e., during oral health) (Palmer et al, 2006; Periasamy and Kolenbrander, 2009a,b, 2010; Zhou et al, 2016)
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