Criblamydia sequanensis

Domain: Bacteria
Phylum: Chlamydiae
Class: Chlamydia
Order: Chlamydiales
Family: Chlamydiaceace
Genus: Criblamydia
Species: C. sequanensis

Criblamydia sequanensis is a nonmotile, star-shaped, obligately intracellular bacterium that grows within host-derived vacuoles. C. sequanensis grows in high numbers in amoebae, and exhibits a developmental cycle consistent with other Chlamydia species. C. sequanensis belongs to the class Chlamydia and was the first species to be identified in the Criblamydia genus. C. sequanensis was recovered from a water sample from the river Seine in France and co-cultivated with the amoeba Acanthamoeba castellanii ATCC 30010.

Discovery

C. sequanensis was isolated from a sample of water from the Seine river, near the entry of the Morsang-sur-Seine drinking water plant. Environmental samples from this location were generally shown to display bacterial overgrowth with amoebal lysis or encystment, therefore the samples underwent a pan-Chlamydiales specific polymerase chain reaction (PCR) for screening each well of amoebal co‐culture. Of the eight water samples that were screened, two were found to be positive for Chlamydiales specific primers. These samples were cultured along with Acanthamoeba castellanii for a period of 6 to 14 days. Following this subculturing of these two samples took place with A. castellanii and ampicillin and vancomycin, which led to the recovery of two strains of chlaymdia-like bacteria. One of the two would go on to be proposed as a new species of Chlamydiales, named Criblamydia sequanensis. Criblamydia was derived from the abbreviation CRIB which stands for the Center for Research on Intracellular Bacteria. Sequanisis comes from the Latin name for the Seine River.

Morphology

C. sequanensis is 0.5-1µm in diameter. Transmission electron microscopy showed the organism to have a star-shaped body, a trait unique in comparison to most other clamydiae.

Genome and Phylogeny

The genome of C. sequanensis was first sequenced in 2014 and has a total number of 2,969,604 bases, with a guanine-cytosine (G-C) content of 38.2 %. The chromosome is one of the largest within the chlamydiales order, and contains 2476 genes in total, with 2416 of these genes being protein encoding. The function of the protein coding genes is predicted in 66% percent of these genes.

Sequencing of the 16s rRNA encoding gene showed the closest similarity with Parachlamydiaceae (88.5–89.8%), followed by Waddliaceae (87.1-88.3%), Chlamydiaceae (86.2–87.2%), Simkaniaceae (84.7–85.6%) and Rhabdochlamydiaceae (84.9–85.2%), showing closest similarity within the Chlaymdiales order. Furthering sequencing of the 23s rRNA sequence again showed the closest similarity to Chlamydiales, with the highest being Waddliaceae (84.8–87.4%), followed by Parachlamydiaceae (82.2–85.2%), Simkaniaceae (80.0–83.1%) and Chlamydiaceae (77.6–80.4%).

Additionally, C. sequanensis possesses a circular plasmid, made up of 89, 525 base pairs, with a G-C conetent of 40.8%. This megaplasmid encodes 92 proteins. 48% of these proteins are conserved with an unknown function. Interestingly the proteins appear to be from various different origins. A BLAST search indicated the highest similarity to Chlamydiales and Proteobacteria (each 25%). Other notable similarities included a 7% similarity to Bacteriodetes and a 5% similarity to Firmicutes. Further, 7% of the proteins were found to be of phagic origin. This sequenced plasmid will allow for researchers to further investigate the genetic background of C. sequanensis, as well as the evolution of chlamydial plasmids.