Mycoplasma genitalium Nonadherent Phase Variants Arise by Multiple Mechanisms and Escape Antibody-Dependent Growth Inhibition

Abstract

Antigenic variation of the immunodominant MgpB and MgpC proteins has been suggested to be a mechanism of immune evasion of the human pathogen , a cause of several reproductive tract disease syndromes. Phase variation resulting in the loss of adherence has also been documented, but the molecular mechanisms underlying this process and its role in pathogenesis are still poorly understood. In this study, we isolated and characterized 40 spontaneous, nonadherent phase variants from-passaged cultures. In all cases, nonadherence was associated with the loss of MgpBC protein expression, attributable to sequence changes in the expression site. Phase variants were grouped into seven classes on the basis of the nature of the mutation. Consistent with the established role of RecA in phase variation, 31 (79.5%) variants arose via recombination with MgPa repeat regions that contain variable sequences. The remaining mutants arose via nonsense or frameshift mutations. As expected, revertants were obtained for phase variants that were predicted to be reversible but not for those that arose via an irreversible mechanism. Furthermore, phase variants were enriched in cultures exposed to antibodies reacting to the extracellular, conserved C terminus of MgpB but not in cultures exposed to antibodies reacting to an intracellular domain of MgpB or the cytoplasmic HU protein. Genetic characterization of the antibody-selected phase variants confirmed that they arose via reversible and irreversible recombination and point mutations within These phase variants resisted antibody-mediated growth inhibition, suggesting that phase variation promotes immune evasion.

Functional Characterization of the Cell Division Gene Cluster of the Wall-less Bacterium Mycoplasma genitalium

“…A few years ago, we documented that deletion of the ftsZ gene abrogated the occurrence of non-adherent phase variants in M. genitalium ( Lluch-Senar et al, 2010 ). These non-adherent variants arise at relatively high frequencies and may play an important role to evade the immune response during infection ( Burgos et al, 2018 ). Based on this observation, we proposed that FtsZ could be important for cell division in non-adherent cells of M. genitalium .…”

Sequence variation and immunogenicity of the Mycoplasma genitalium MgpB and MgpC adherence proteins during persistent infection of men with non-gonococcal urethritis

“…Phase variants arise in vitro by multiple mechanisms including recombination between mgpBC and the MgPars, point mutations, and deletions. [25,33,34]. Phase variants generated by recombination fall into at least six classes and can be reversible or irreversible depending on the number of recombination partners involved [33].…”

“…[25,33,34]. Phase variants generated by recombination fall into at least six classes and can be reversible or irreversible depending on the number of recombination partners involved [33]. Deletion of recA results in the near-total loss of antigenic and phase variation implicating recombination as the mechanism that generates the majority of these variants [25,33].…”

Subversion of the Immune Response by Human Pathogenic Mycoplasmas

“…Hence, it is usually considered that high-frequency antigenic variation occurs only in the variable regions of MG191/MG192. Interestingly, mgpB / C phase variants lacking adherence properties were still able to evade killing by antibodies and complement through avoiding antibody recognition of their variable regions (Burgos et al, 2018). This result indicates that M. genitalium could also escape antibody-mediated killing by virtue of altering its conserved C-terminal domain.…”