Diversity in Chlamydial plasmids

Abstract

BackgroundEvolutionary studies have been conducted that have investigated the chromosomal variance in the genus of Chlamydia. However, no all-encompassing genus-wide comparison has been performed on the plasmid. Therefore, there is a gap in the current knowledge on Chlamydia plasmid diversity. AimsThis project is aimed to investigate and establish the nature and extent of diversity across the entire genus of Chlamydia, by comparing the sequences of all currently available plasmid carrying strains. MethodsThe PUBMED database was used to identify plasmid sequences from all available strains that met the set quality criteria for their inclusion in the study. Alignments were performed on the 51 strains that fulfilled the criteria using MEGA X software. Following that Maximum Likelihood estimation was used to construct 11 phylogenetic trees of the whole plasmid sequence, the individual 8 coding sequences, the iteron and a chromosomal gene ompA as a comparator. ResultsThe genus-wide plasmid phylogeny produced three distinct lineages labelled as alpha, beta and gamma. Nineteen genotypes were found in the initial whole plasmid analysis. Their distribution was allocated as six C. pecorum, two C. pneumoniae, one C. gallinacea, one C. avium, one C. caviae, one C. felis, two C. psittaci, one C. trachomatis, one C. muridarum, and two C. suis. The chromosomal comparative gene ompA supported this distribution, with the same number of primary clades with the same species distribution. However, ompA sequence comparison resulted in fewer genotypes due to a reduced amount of available sequences (33 out of 51). All results were statistically significant.

Coevolving Plasmids Drive Gene Flow and Genome Plasticity in Host-Associated Intracellular Bacteria

“…Consistent with this, the almost entirely vertical transmission of this gene family has been observed earlier for C. trachomatis strains 42 and the genus Chlamydia in general. 40 A decisive event occurred during the divergence of the ancestor of the Parachlamydiaceae, Criblamydiaceae, and Waddliaceae, and the ancestor of the Chlamydiaceae and Clavichlamydiaceae ( Figure 1). The ancestral plasmid of the latter gained pgp4, which today is a key plasmid specific transcription factor of virulence genes for in vivo pathogenicity in the Chlamydiaceae.…”

“… 35 , 36 , 37 , 38 Accumulating evidence indicates coevolution of chlamydial plasmids and chromosomes within the family Chlamydiaceae. 39 , 40 , 41 , 42 HGT among Chlamydia trachomatis strains is common, and both intra- and inter-species HGT has been demonstrated experimentally, 43 , 44 , 45 yet the role of plasmids therein is unclear. Intriguingly, all other chlamydial families with cultured representatives have members with plasmids up to 145.3 kb in size.…”

Chlamydiae – what’s new?

“…They include eight coding sequences and non-coding RNA with unknown functionality ( 47 ). Generally, plasmids can be carriers of antibiotic resistance genes, but to date, there has been no evidence presented of antibiotic resistance located on chlamydial plasmids ( 70 ). Plasmids were found in the majority of chlamydial genomes: in C. trachomatis , C. psittaci , C. pecorum , C. avium , C. caviae , C. felis , C. muridarum , C. suis , C. pneumoniae , C. buteonis , C. gallinacea , C. poikilothermis , C. serpentis , Cand .…”

“…C. testudinis ( 6 , 36 , 37 , 56 , 68 , 77 , 80 , 84 ). Until recently, it was thought that no plasmid existed in the C. abortus genome ( 47 , 70 ), but surprisingly, the genomes of the recently described avian strains have a plasmid homologous to that found in C. psittaci ( 75 , 88 ). According to the latest data, a plasmid is apparent in the genome of the common bacterial ancestor of all the species, but with time, the plasmids have diverged.…”

“…It is assumed that because of the high level of conservation across the Chlamydia genus (excluding C. pneumoniae ), there is a strong evolutionary selection for these species retaining their plasmids. Moreover, based on the performed evolutionary analysis it is assumed that the plasmid and the chromosome have co-evolved ( 70 ).…”