However, inasmuch as these types of shifts in environmental conditions represent artificial in vitro manipulations that cannot fully mimic the spirochete’s natural habitats [37, 41, 42], there may be other aspects of RpoN-RpoS pathway activation that have not yet been appreciated using such in vitro culture conditions as surrogates for natural stimuli. In an attempt to garner more biologically relevant Selleck AZD2281 gene expression information and to determine at what specific

phase(s) of the enzootic life cycle of B. burgdorferi the RpoN-RpoS pathway is induced and may remain active, we examined the expression of rpoS and selected target genes of RpoS over the entire tick-mammalian enzootic life cycle. Results and discussion Although in vitro gene expression data have suggested that the RpoN-RpoS pathway is most robust at the tick-mammal transmission interface [9, 17, 21, 36, 38–40, 43], comprehensive gene expression analysis data to support this contention by assessing actual tick and mammalian tissues have been lacking. Furthermore, heretofore, activation of the pathway over the broader tick-mammalian cycle has not been assessed. To address this dearth of information, we examined the expression of rpoS throughout the complete infectious life cycle of B. burgdorferi. rpoS transcription is activated during tick feeding and remains active

during mammalian infection by B. burgdorferi R788 manufacturer In Cell press vitro, rpoS is markedly induced in spirochetes cultivated under conditions that largely mimic tick engorgement, suggesting that rpoS expression is robust during the early transmission phase. Herein, our qRT-PCR analyses indicated that, in larval ticks during acquisition, only 0.4 copies of rpoS transcripts per 100 flaB transcripts were detected in fed larvae, and no rpoS transcripts were detected in intermolt larvae (Figure 1A). However, when exposed to a blood meal, rpoS transcription

was dramatically induced; in nymphal ticks following 24, 48, or 72 hours of feeding, 1.8, 3.4, or 8.2 copies of rpoS transcripts per 100 flaB transcripts were detected, respectively (Figure 1A). These data suggest that RpoS is synthesized actively during nymphal tick feeding, and that RpoS then likely transcribes its gene targets. Previously, Caimano et al. [17] reported an increase in rpoS transcripts in engorged infected nymphs (collected at 6-8 days post feeding to repletion). Our more recent data not only are consistent with the findings of Caimano et al. [17], but further pinpoint that the activation of rpoS expression occurs initially in nymphal ticks upon blood feeding. Figure 1 qRT-PCR analysis of rpoS transcription in ticks and in mouse tissues. A, flat (uninfected) larvae, fed larvae, intermolt larvae, and fed nymphs during transmission phase were collected at 24-, 48-, and 72-h post-feeding. TT: tick transmission.