Yersinia pestis autoagglutination factor is a component of the type six secretion system

Autoagglutination (AA) is a protective phenotypic trait facilitating survival of bacteria in hostile environments and in the host during infection. Autoagglutination factors (AFs) that possess self-associating ability are currently characterized in many Gram-negative bacteria, but Yersinia pestis AFs are still a matter of debate. Previously, we have shown that AF of Hms(-) strain Y. pestis EV76 is a complex of the 17,485-kDa protein and a low-molecular-weight component with siderophore activity. Here, we identified the protein moiety of AF and examined its role in AA of Hms(+) and Hms(-)Y. pestis strains. Using MALDI-TOF MS of trypsin-hydrolyzed AF, we unambiguously identified the protein as YPO0502, which belongs to a family of Hcp-proteins forming pilus-like structures of the type six secretion system (T6SS). To address the role of YPO0502 in AA, we cloned ypo0502 in E. coli, overexpressed it in Y. pestis and constructed its knock-out mutant in Y. pestis. However, all these approaches failed: YPO0502 was not secreted in E. coli, formed inclusion bodies when overexpressed in Y. pestis, and could probably be compensated by other Hcp-like proteins in Y. pestis. In contrast, downregulation of ypo0502 expression by its antisense RNA supported the contribution of YPO0502 in AA of Hms(+) and Hms(-)Y. pestis strains. The results of the present study indicate that the Hcp-like component of T6SS encoded by ypo502 is involved in Y. pestis AA and suggest that at least one (ypo0499-0516) of the 6 T6SS clusters of Y. pestis is involved in bacterial interaction.