mgpB and mgpC sequence diversity in Mycoplasma genitalium is generated by segmental reciprocal recombination with repetitive chromosomal sequences.

Mycoplasma genitalium is associated with sexually transmitted infections in men and women that, if untreated, can persist, suggesting that mechanism(s) exist to facilitate immune evasion. Approximately 4% of the limited M. genitalium genome contains repeat sequences termed MgPar regions that have homology to mgpB and mgpC, which encode antigenic proteins associated with attachment. We have previously shown that mgpB sequences vary within a single strain of M. genitalium in a pattern consistent with recombination between mgpB and MgPar sequences (Iverson-Cabral et al.). In the current study, we show that mgpC heterogeneity similarly occurs within the type strain, G-37(T), cultured in vitro and among cervical specimens collected from a persistently infected woman. In all cases, alternative mgpC sequences are indicative of recombination with MgPar regions. Additionally, the isolation of single-colony M. genitalium clonal variants containing alternative mgpB or mgpC sequences allowed us to demonstrate that mgpB and mgpC heterogeneity is associated with corresponding changes within donor MgPar regions, consistent with reciprocal recombination. Better-defined systems of antigenic variation are typically mediated by unidirectional gene conversion, so the generation of genetic diversity observed in M. genitalium by the mutual exchange of sequences makes this organism unique among bacterial pathogens.