2022/07/07 by Max Emil Schön, Joran Martijn, Julian Vosseberg +2 · 1 citation
Biochemistry, Genetics and Molecular Biology · Environmental Science · Agricultural and Biological Sciences · #Genomics and Phylogenetic Studies #Microbial Community Ecology and Physiology #Insect symbiosis and bacterial influences
paper · pdf · doi:10.1038/s41564-022-01169-x
openalex publication_date 2022/07/07 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/01
The evolution of obligate host-association of bacterial symbionts and pathogens remains poorly understood. The Rickettsiales are an alphaproteobacterial order of obligate endosymbionts and parasites that infect a wide variety of eukaryotic hosts, including humans, livestock, insects and protists. Induced by their host-associated lifestyle, Rickettsiales genomes have undergone reductive evolution, leading to small, AT-rich genomes with limited metabolic capacities. Here we uncover eleven deep-branching alphaproteobacterial metagenome assembled genomes from aquatic environments, including data from the Tara Oceans initiative and other publicly available datasets, distributed over three previously undescribed Rickettsiales-related clades. Phylogenomic analyses reveal that two of these clades, Mitibacteraceae and Athabascaceae, branch sister to all previously sampled Rickettsiales. The third clade, Gamibacteraceae, branch sister to the recently identified ectosymbiotic 'Candidatus Deianiraea vastatrix'. Comparative analyses indicate that the gene complement of Mitibacteraceae and Athabascaceae is reminiscent of that of free-living and biofilm-associated bacteria. Ancestral genome content reconstruction across the Rickettsiales species tree further suggests that the evolution of host association in Rickettsiales was a gradual process that may have involved the repurposing of a type IV secretion system.