Transmission Factors: Yersinia pestis Genes Required to Infect the Flea Vector of Plague
Y. pestis Ymt and Hms proteins have complementary but distinct roles. Ymt is required for survival in the midgut compartment, but not the proventriculus compartment, of the flea digestive tract. Conversely, the hms genes are not required to infect the midgut, but are required to infect the proventriculus. In addition to ymt and hms, the outer surface plasminogen activator of Y. pestis is considered to be important for fleaborne transmission, although this role does not occur in the flea (Hinnebusch et al., 1998). Sodeinde et al., (2002) showed that Pla is important for dissemination from a subcutaneous inoculation site in mice. This finding suggested that pla is pertinent to the fleaborne life-cycle of Y. pestis, which demands that the bacteria be able to disseminate from the dermis where they are deposited by a flea. Notably, ymt and pla are located on plasmids that are unique to Y. pestis. Thus, acquisition of these two plasmids by horizontal transfer helps to account for the rapid evolutionary transition of Y. pestis to fleaborne transmission within the last 20,000 years.
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