Natural competence in Chlorogloeopsis fritschii PCC 6912 and other ramified cyanobacteria

Lateral DNA transfer plays an important role in the evolution of genetic diversity in prokaryotes. DNA acquisition via transformation involves the uptake of DNA from the environment. The ability of recipient cells to actively transport DNA into the cytoplasm - termed natural competence - depends on the presence of type IV pili and competence proteins. Natural competence has been described in cyanobacteria for several organisms including unicellular and filamentous species. However, the presence of natural competence in ramified cyanobacteria, which are considered the peak of cyanobacterial morphological complexity, remains unknown. Here we show that ramified cyanobacteria harbour the genes essential for natural competence and experimentally demonstrate natural competence in the ramified cyanobacterium Chlorogloeopsis fritschii PCC 6912 (hereafter Chlorogloeopsis). Searching for homologs to known natural competence genes in ramified cyanobacteria showed that these genes are conserved in the majority of tested isolates. Experimental validation of natural competence using several alternative protocols demonstrates that Chlorogloeopsis could be naturally transformed with a replicative plasmid. Our results show that natural competence is a common trait in ramified cyanobacteria and that natural transformation is likely to play an important role in cyanobacteria evolution. ImportanceCyanobacteria are crucial players in the global biogeochemical cycles where they contribute to CO2- and N2-fixation. Their main ecological significance is the oxygen-producing photosynthetic apparatus that contributes to contemporary food chains. Ramified cyanobacteria form true-branching and multiseriate cell filament structures that represent a peak of prokaryotic multicellularity. Species in that group inhabit fresh and marine water habitats, thermal springs, arid environments, as well as endolithic and epiphytic habitats. Here we show that ramified cyanobacteria harbor the mechanisms required for DNA acquisition via natural transformation. The prevalence of mechanisms for natural uptake of DNA has implications for the role of DNA acquisition in the evolution of cyanobacteria. Furthermore, presence of mechanisms for natural transformation in ramified cyanobacteria opens up new possibilities for genetic modification of ramified cyanobacteria.