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. 2019 Aug 21;10:1923. doi: 10.3389/fmicb.2019.01923

FIGURE 2.

FIGURE 2

ospA is expressed throughout the entire tick phase of the enzootic cycle. (A) Cartoon depicting the tandem insertion of a PospA-gfp/PflgB tdTomato “dual color” cassette into the cp26 bbb21-22 intergenic region (Kawabata et al., 2004); the resulting B. burgdorferi strain was designated BbP1981. The upstream region used to monitor expression of ospA (PospA) includes sequences required for RpoS-mediated repression of the ospA in mammals (Grove et al., 2017). (B) Representative quad-plots for temperature-shifted in vitro PospA-gfp +/tdTomato+ double-positive spirochetes. Numbers indicate the percentage of positive events in each quadrant. (C) Representative epifluorescence images of the PospA-gfp/PflgB-tdTomato dual color strain (BbP1981) following temperature-shift at 37°C in vitro; cultivation in DMCs; in I. scapularis larvae fed to repletion on BbP1981-infected C3H/HeJ mice; in unfed nymphs; in BbP1981-infected nymphs fed for 72–96 h on a naïve C3H/HeJ mice (Transmission Nymphs); and in naïve nymphs fed for ∼36–48 h on C3H/HeJ mice 4 weeks post-infection (Acquisition Nymphs). Scale bar, 20 μm.