The indication here is that Borrelia burgdorferi assumes a round body form within the tick in order to survive until circumstances for transmission to the host are present. There is no confirmation here, however, of its formation in vivo within a host mammal...
Full Text Source: http://www.plospathogens.org/article/info%3Adoi%2F10.1371%2Fjournal.ppat.1002532
Borrelia burgdorferi Requires the Alternative Sigma Factor RpoS for Dissemination within the Vector during Tick-to-Mammal Transmission
Star M. Dunham-Ems, Melissa J. Caimano, Christian H. Eggers, Justin D. Radolf
While the roles of rpoSBb and RpoS-dependent genes have been studied extensively within the mammal, the contribution of the RpoS regulon to the tick-phase of the Borrelia burgdorferi enzootic cycle has not been examined. Herein, we demonstrate that RpoS-dependent gene expression is prerequisite for the transmission of spirochetes by feeding nymphs. RpoS-deficient organisms are confined to the midgut lumen where they transform into an unusual morphotype (round bodies) during the later stages of the blood meal. We show that round body formation is rapidly reversible, and in vitro appears to be attributable, in part, to reduced levels of Coenzyme A disulfide reductase, which among other functions, provides NAD+ for glycolysis. Our data suggest that spirochetes default to an RpoS-independent program for round body formation upon sensing that the energetics for transmission are unfavorable.
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