Naturally competent organisms are capable of DNA uptake directly from the environment through the process of transformation. Despite the importance of transformation to microbial evolution, DNA uptake remains poorly characterized outside of the bacterial domain. Here, we identify the pilus as a necessary component of the transformation machinery in archaea. We describe two naturally competent organisms, Methanococcus maripaludis and Methanoculleus thermophilus In M. maripaludis, replicative vectors were transferred with an average efficiency of 2.4 × 10 3 transformants μg -1 DNA. In M. thermophilus, integrative vectors were transferred with an average efficiency of 2.7 × 10 3 transformants μg -1 DNA. Additionally, natural transformation of M. thermophilus could be used to introduce chromosomal mutations. To our knowledge, this is the first demonstration of a method to introduce targeted mutations in a member of the order Methanomicrobiales For both organisms, mutants lacking structural components of the type IV-like pilus filament were defective for DNA uptake, demonstrating the importance of pili for natural transformation. Interestingly, competence could be induced in a noncompetent strain of M. maripaludis by expressing pilin genes from a replicative vector. These results expand the known natural competence pili to include examples from the archaeal domain and highlight the importance of pili for DNA uptake in diverse microbial organisms. IMPORTANCE Microbial organisms adapt and evolve by acquiring new genetic material through horizontal gene transfer. One way that this occurs is natural transformation, the direct uptake and genomic incorporation of environmental DNA by competent organisms. Archaea represent up to a third of the biodiversity on Earth, yet little is known about transformation in these organisms. Here, we provide the first characterization of a component of the archaeal DNA uptake machinery. We show that the type IV-like pilus is essential for natural transformation in two archaeal species. This suggests that pili are important for transformation across the tree of life and further expands our understanding of gene flow in archaea.
Bibliographical noteFunding Information:
Experiments on M. maripaludis were sponsored by the Army Research Office and were accomplished under grant number W911NF-19-1-0024. Experiments on M. thermophilus were supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences under grant number DE-SC0019148. D.R.F. was supported by the National Science Foundation Graduate Research Fellowship Program under grant number CON-75851.
© 2020 American Society for Microbiology.
- Methanococcus maripaludis
- natural competence
- type IV-like pili