pylori orientation [24]. In contrast, bicarbonate and not CO2 appears to be the selleck chemical inducer of expression of the B. anthracis toxins [25]. Using the P ebpA ::lacZ fusion in OG1RF, we first investigated the independent effect of CO2 and NaHCO3 on ebpA in buffered TSBG with or without the presence of 0.1 M NaHCO3 and/or 5% CO2. pH was controlled during the experiment and remained at pH 7.5 ± 0.25. As shown in Fig. 7, ebpA expression in TSBG-air did not differ appreciably from that in TSBG- 5% CO2, reaching

a peak of expression early in stationary phase (15.8 and 14.5 β-gal units, respectively); expression then decreased to 2 and 0.4 β-gal units, respectively, at 24 hr. In the presence of NaHCO3, ebpA expression peak was ~4-fold higher with 46.5 β-gal units for the NaHCO3-air culture at entry into stationary phase (5 hr) compared to 9.8 β-gal when the cells were grown without NaHCO3, and 46.0 β-gal units for the click here 5% CO2 plus NaHCO3 culture compared to 12.5 β-gal when grown in presence of CO2 only. The bicarbonate effect persisted late into stationary

phase with 42.5 and 40.7 β-gal units when grown in air-NaHCO3 and CO2-NaHCO3 respectively. A similar profile with increased ebpR expression in the presence of bicarbonate but not in presence of CO2 was also observed (data not shown). Furthermore, the differential effect of CO2 and NaHCO3 was also detected in BHI or when potassium bicarbonate was used as a source for HCO3 – (data not shown). Taken together, these results demonstrate that the increase in ebpR and ebpA expression is caused by the addition of HCO3 – and not CO2. Figure 7 ebpA expression affected by NaHCO 3 , and not CO 2 . For β-gal assays, samples were collected every hour from 3 to 8 hr, then at 10 and 24 hr after starting the culture (x axis). Growth

curves of OG1RF containing P ebpA ::lacZ are shown in air with a thin gray line, in NaHCO3/air with thin orange line, in CO2 with a dense gray line, and in NaHCO3/CO2 with a dense orange line. The Clomifene β-gal assays for OG1RF containing P ebpA ::lacZ are represented with closed black square, closed orange square, open black square, and open orange square when the cells were grown in air, 5% CO2, NaHCO3-air, and NaHCO3-5% CO2, respectively. All sets of cultures presented were analyzed concurrently. This figure is a representative of at least two experiments. A. OD600 nm readings. B. β-gal assays (β-gal units = OD420 nm/protein concentration in mg/ml). Since NaHCO3 is in equilibrium with H2CO3, HCO3-, and CO3 2- depending of the pH, temperature and partial pressure of CO2, we next tested a possible pH effect on ebpA expression when cells were grown in buffered TSBG. In a preliminary experiment, OG1RF (P ebpA ::lacZ) was grown in buffered TSBG with pH ranging from 5 to 9. Severe growth inhibition was observed at pH 5 and 9 with mild growth inhibition at pH 6, compared to unaffected growth at pH 7 and 8 (data not shown).