Gain of Function Analysis Reveals Non-Redundant Roles for theYersinia pestisType III Secretion System Effectors YopJ, YopT, and YpkA

Abstract

AbstractVirulence ofYersinia pestisin mammals requires the type III secretion system, which delivers seven effector proteins into the cytoplasm of host cells to undermine immune responses. All seven of these effectors are conserved acrossY. pestisstrains, but three – YopJ, YopT, and YpkA – are apparently dispensable for virulence. Some degree of functional redundancy between effector proteins would explain both observations. Here, we use a combinatorial genetic approach to define the minimal subset of effectors required for full virulence in mice following subcutaneous infection. We found that aY. pestisstrain lacking YopJ, YopT, and YpkA is attenuated for virulence in mice, and that addition of any one of these effectors to this strain increases lethality significantly. YopJ, YopT, and YpkA likely contribute to virulence via distinct mechanisms. YopJ is uniquely able to cause macrophage cell deathin vitroand to suppress accumulation of inflammatory cells to foci of bacterial growth in deep tissue, whereas YopT and YpkA cannot. The synthetic phenotypes that emerge when YopJ, YopT, and YpkA are removed in combination provide evidence that each enhancesY. pestisvirulence, and that YopT and YpkA act through a mechanism distinct from that of YopJ.