The Fish Pathogen “CandidatusClavichlamydia salmonicola”—A Missing Link in the Evolution of Chlamydial Pathogens of Humans

Abstract

Chlamydiae like Chlamydia trachomatis and Chlamydia psittaci are well-known human and animal pathogens. Yet, the chlamydiae are a much larger group of evolutionary ancient obligate intracellular bacteria that includes predominantly symbionts of protists and diverse animals. This makes them ideal model organisms to study evolutionary transitions from symbionts in microbial eukaryotes to pathogens of humans. To this end, comparative genome analysis has served as an important tool. Genome sequence data for many chlamydial lineages are, however, still lacking, hampering our understanding of their evolutionary history. Here, we determined the first high-quality draft genome sequence of the fish pathogen “Candidatus Clavichlamydia salmonicola”, representing a separate genus within the human and animal pathogenic Chlamydiaceae. The “Ca. Clavichlamydia salmonicola” genome harbors genes that so far have been exclusively found in Chlamydia species suggesting that basic mechanisms important for the interaction with chordate hosts have evolved stepwise in the history of chlamydiae. Thus, the genome sequence of “Ca. Clavichlamydia salmonicola” allows to constrain candidate genes to further understand the evolution of chlamydial virulence mechanisms required to infect mammals.

Chlamydiae in corals: shared functional potential despite broad taxonomic diversity

“…Mutations in the hemG gene, involved in heme synthesis, were associated with increased infectivity in C. trachomatis [ 66 ], suggesting that the presence or absence of the heme biosynthesis pathway may lead to different infection outcomes. Despite this difference, the overall gene content similarities among marine Simkania are consistent with previous studies finding that chlamydiae in general have a large core genome [ 29 , 44 , 67 , 68 ], with similar metabolic abilities and lifestyle features, such as energy parasitism and a biphasic developmental cycle. The lack of recognizable host-driven genomic convergence in several chlamydial groups may provide more host flexibility and explain the wide range of eukaryotic hosts they have successfully formed associations with.…”

Distinct impacts of each anti-anti-sigma factor ortholog of the chlamydial Rsb partner switching mechanism on development inChlamydia trachomatis

“…The phylum Chlamydiota is comprised of obligate intracellular Gram negative bacteria infecting a variety of eukaryotic hosts such as amoeba, invertebrates, and vertebrates including fish, reptiles, birds, and mammals (1). Like most obligate intracellular bacteria, they have reduced genomes varying in size from 1 Mbp to ~2.5 Mbp, and genome content impacts their endosymbiotic host range by dictating, for example, metabolic capacity/parasitic requirements, cell entry mechanisms, stress response pathways, and protein effector repertoires needed to survive in the face of different innate and adaptive immune responses (2)(3)(4)(5). Despite variation in hosts and endosymbiotic requirements, all characterized members of the phylum undergo a developmental cycle involving differentiation of the infectious elementary body (EB) into the replicative reticulate body (RB) (primary differentiation) followed by replication of RBs and the eventual conversion of RBs into EBs (secondary differentiation) (6,7).…”