Genetic Variation in the Complete MgPa Operon and Its Repetitive Chromosomal Elements in Clinical Strains of Mycoplasma genitalium

Abstract

Mycoplasma genitalium has been increasingly recognized as an important microbe not only because of its significant association with human genital tract diseases but also because of its utility as a model for studying the minimum set of genes necessary to sustain life. Despite its small genome, 4.7% of the total genome sequence is devoted to making the MgPa adhesin operon and its nine chromosomal repetitive elements (termed MgPars). The MgPa operon, along with 9 MgPars, is believed to play an important role in pathogenesis of M. genitalium infection and has also served as the main target for development of diagnostic tools. However, genetic variation in the complete MgPa operon and MgPars among clinical strains of M. genitalium has not been addressed. In this study we examined the genetic variation in the complete MgPa operon (approximately 8.5 kb) and full or partial MgPar sequences (0.4–2.6 kb) in 15 geographically diverse strains of M. genitalium. Extensive variation was present in four repeat regions of the MgPa operon (with homology to MgPars) among and within strains while the non-repeat regions (without homology to MgPars) showed low-level variation among strains and no variation within strains. MgPars showed significant variation among strains but were highly homogeneous within strains, supporting gene conversion as the likely recombination mechanism. When applying our sequence data to evaluate published MgPa operon-based diagnostic PCR assays and genotyping systems, we found that 11 of 19 primers contain up to 19 variable nucleotides and that the target for one of two typing systems is located in a hypervariable repeat region, suggesting the likelihood of false results with some of these assays. This study not only provides new insights into the role of the MgPa operon in the pathogenesis of M. genitalium infection but has important implications for the development of diagnostic tools.

Inter- and Intra-Strain Variability of Tandem Repeats in Mycoplasma Pneumoniae Based on Next-Generation Sequencing Data

“…19294) showed ten alleles at P1-AGT with repeat copy number varying from 8 to 19 (Supplementary Table 12), suggesting an extreme instability of this locus. Interestingly, the P1-AGT repeat of M. pneumoniae has a counterpart in M. genitalium, which is located in the MPN141 homolog MG191 and which is also hypervariable among and within M. genitalium strains [19][20]22]. The conservation of this repeat across species and its hypervariability within each species implies an important role in functional consequences, presumably in adaptation and pathogen-host interactions [8,22].…”

“…These loci have been frequently used as the targets for molecular typing to help understand the epidemiology and pathogenesis of both pathogens [13][14][15][16][17][18]. Of note, numerous studies of VNTRs in M. genitalium have demonstrated extensive intrastrain repeat number variations despite its genome size being the smallest among all sequenced mycoplasma species [14,[18][19][20][21][22][23][24], whereas there has been a scarcity of reports of such variations in M. pneumoniae [25] and other mycoplasma species. It is unknown whether this difference reflects intrinsic genomic divergence between different species or technical limitations of the detection methods used.…”

Genetic Variation inMycoplasma genitalium

“…The gene for MgPa is composed of one operon that contains three genes; MG190 (mgpA), MG191 (mgpB), and MG192 (mgpC), with minimal inter-spacer regions among them (Fig. 3) [31,39,40]. The gene for MgPa is a single, continuous copy; however, there are nine repetitive MgPar elements in the truncated copies of MG191 and MG192 genes dispersed throughout the genome (Fig.…”

“…The gene for MgPa is a single, continuous copy; however, there are nine repetitive MgPar elements in the truncated copies of MG191 and MG192 genes dispersed throughout the genome (Fig. 3) [31,39,40]. The MgPar DNA sequences have a partial similarity with the B, EF, and G areas in the MgPa gene, suggesting the possibility of genetic recombination [31,[39][40][41][42].…”

“…The role of MgPa protein in MG includes the attachment of bacteria onto the host epithelium, invasion into the host cells, and provide an immunogenic role for the host immune system [33,37,39,40]. We performed a multiple comparison analysis with 20 different MG191 partial DNA sequences from the National Center for Biotechnology Information (NCBI) database (Supplementary Table 1) [49].…”