Gene conversion accounts for pilin structural changes and for reversible piliation “phase” changes in gonococci

Abstract

Pilus⁺ “wild-type” gonococci (Gc) frequently display gene conversion of their expressed complete pilin gene (CPG); a copy of DNA derived from one of the Gc genome's multiple silent partial pilin genes (PPG) is recombinationally-inserted into the CPG's central and 3′ portions with formation of a new, chimeric CPG. Expression of that new CPG leads to either 1) retention of pilus⁺ phenotype but change in pilin primary structure/antigenicity, or 2) phase change to pilus⁻ phenotype capable of reverting. This study utilizes pilus revertants of P⁻ rp±Gc and P⁺ colony morphotye variants spawned by P⁺⁺ Gc to examine pilin gene conversion in strain MS11_mk Gc in greater detail. Each revertant's and variant's expressed pilin gene's sequence (as pilin mRNA) was defined to learn whether their differences are due to gene conversion by different PPGs, or by varying stretches from the same PPG, or both. Gene conversion by PPG pilS1 copy 2 has been documented in Gc recovered from a human voluteer's urethra previously inoculated with pilus Gc (strain MS11). The pilus⁺ Gc isolated expressed structurally/antigenically distinct pilins.