Kinetics of Genetic Variation of the Mycoplasma genitalium MG192 Gene in Experimentally Infected Chimpanzees

Abstract

Mycoplasma genitalium, a human pathogen associated with sexually transmitted diseases, is capable of causing chronic infections, though mechanisms for persistence remain unclear. Previous studies have found that variation of the MgPa operon occurs by recombination of repetitive chromosomal sequences (known as MgPars) into the MG191 and MG192 genes carried on this operon, which may lead to antigenic variation and immune evasion. In this study, we determined the kinetics of MG192 sequence variation during the course of experimental infection using archived specimens from two chimpanzees infected with M. genitalium strain G37. The highly variable region of MG192 was amplified by PCR from M. genitalium isolates obtained at various time points postinfection (p.i.). Sequence analysis revealed that MG192 sequence variation began at 5 weeks p.i. With the progression of infection, sequence changes accumulated throughout the MG192 variable region. The presence of MG192 variants at specific time points was confirmed by variant-specific PCR assays and sequence analysis of single-colony cloned M. genitalium organisms. MG192 nucleotide sequence variation correlated with estimated recombination events, predicted amino acid changes, and time of seroconversion, a finding consistent with immune selection of MG192 variants. In addition, we provided evidence that MG192 sequence variation occurred during the process of M. genitalium single-colony cloning. Such spontaneous variation suggests that some MG192 variation is independent of immune selection but may form the basis for subsequent immune selection.

FIG 1

Progressive MG192 sequence variation during the course of M. genitalium infection in two chimpanzees experimentally infected with strain G37^T. The labels below the x axis represent variant sequences identified at various time points as explained in detail in Materials and Methods.

FIG 2

Schematic diagram of representative MG192 variant sequences identified in M. genitalium isolates from a chimpanzee (no. 1125) experimentally infected with strain G37^T. Various patterns in MG192 variants represent regions that are different from the G37^T MG192 sequence and instead have homology to G37^T MgPars, as indicated by the different patterns. Names and approximate locations of primers used in variant-specific PCR are indicated by arrows. See Materials and Methods for variant designations.

FIG 3

Phylogram trees based on the neighbor-joining method using predicted amino acid sequences of MG192 variants obtained from two chimpanzees, A52 and 1125, infected by M. genitalium. Both trees are rooted with the G37^T MG192 sequence, with 1,000 random bootstrap resamplings. Bootstrap values >60% are indicated at nodes. Variants identified from each time point (weeks after inoculation) are enclosed by a dashed oval. See Materials and Methods for variant designations.