Natural competence is a conserved mechanism of horizontal gene transfer that permits massive genetic variation and genomic plasticity via uptake of extracellular DNA. Natural competence requires a contractile pilus system and an assemblage of competence-accessory proteins. Here, we provide evidence that the pilus biogenesis and natural competence in cyanobacteria are regulated by the second messenger c-di-AMP. The c-di-AMP-free (DdacA) mutant showed significantly lower transformation efficiency than the WT cells. Transcriptome and proteome analysis revealed a strong downregulation of specific genes and proteins involved in pilus biogenesis and DNA uptake in the DdacA mutant. These proteins include PilT1, an essential motor required for retraction of type IV pilus. In contrast to WT cells, transmission electron microscopy revealed that dacA cells possess only thick pili with hyperpiliation phenotype similar to the non-competent pilT1 mutant. Furthermore, we show that the competence factor B signaling protein (ComFB) is a novel c-di-AMP-receptor protein, widespread in bacterial phyla. A DcomFB mutant was created to test if ComFB is playing a role in natural competence, and like DdacA mutant, it showed reduced transformation efficiency. Our findings further support that natural competence depends on c-di-AMP signaling and is controlled by a pathway that involves ComFB as a c-di-AMP receptor.

References:

Samir, S., Doello, S., Zimmer, E., Haffner, M., Enkerlin, A. M., Mueller, T., ... & Selim, K. A. (2023). The second messenger c-di-AMP controls natural competence via ComFB signaling protein. bioRxiv, 2023-11.