Abstract
In a previous study, it was shown that Riemerella anatipestifer, a member of Flavobacteriaceae, is naturally competent. However, whether natural competence is universal in Flavobacteriaceae remains unknown. In this study, it was shown for the first time that Riemerella columbina was naturally competent in the laboratory condition; however, Flavobacterium johnsoniae was not naturally competent under the same conditions. The competence of R. columbina was maintained throughout the growth phases, and the transformation frequency was highest during the logarithmic phase. A competition assay revealed that R. columbina preferentially took up its own genomic DNA over heterologous DNA. The natural transformation frequency of R. columbina was significantly increased in GCB medium without peptone or phosphate. Furthermore, natural transformation of R. columbina was inhibited by 0.5 mM EDTA, but could be restored by the addition of CaCl2, MgCl2, ZnCl2, and MnCl2, suggesting that these divalent cations promote the natural transformation of R. columbina. Overall, this study revealed that natural competence is not universal in Flavobacteriaceae members and triggering of competence differs from species to species.
Highlights
Competent bacteria can actively take up naked DNA from their environment and integrate it into the genome, which is called natural transformation (Mell and Redfield, 2014)
R. columbina was cultured in GC broth (GCB) medium with shaking or GCB agar plates and LB plates supplemented with 5% sheep blood at 37◦C, F. johnsoniae was cultured in GCB medium with shaking or GCB plates at 25◦C
The results showed that R. columbina was able to undergo natural transformation; F. johnsoniae was not competent under the same conditions
Summary
Competent bacteria can actively take up naked DNA from their environment and integrate it into the genome, which is called natural transformation (Mell and Redfield, 2014). As one of the three horizontal gene transfer mechanisms, natural transformation facilitates bacterial acquisition of virulence genes and antibiotic-resistant cassettes to help bacteria adapt to the environment (Wiedenbeck and Cohan, 2011; Seitz and Blokesch, 2013a). At least 83 species have been found to have natural competence (Johnston et al, 2014; Liu et al, 2017). In Gram-positive and Gram-negative bacteria, there are different mechanism to take up DNA. Competent Gram-negative bacteria, such as Neisseria species and Haemophilus influenzae, use type IV pili (T4P) to take up exogenous double-stranded DNA (dsDNA), in contrast to Helicobacter pylori, which uses a type IV secretion system (T4SS) (Hofreuter et al, 2000), and Campylobacter jejuni, which uses a type II secretion system (T2SS) (Wiesner et al, 2003)
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