The reaction was performed using the SYBR premix Ex Taq™ (TaKaRa, Dalian, China). The 2-ΔΔCt method was used to calculate relative expression of the VC18166 gene to the VC2414 gene in the N16961 and JS32 strains, and normalized with the control gene recA. ΔΔCt = (CtVC1866 – CtVC1866recA) – (CtVC2414 – CtVC2414recA). CtVC1866recA and CtVC2414recA indicating the Ct values of recA simultaneously amplified with VC1866 and Selleck TPX-0005 VC2414, CtVC1866 and CtVC2414 indicate the Ct values of VC1866 and VC2414. Results Dynamic change of the fermentation medium pH We measured the pH of the sorbitol fermentation media of the strains
during the fermentation test, by extracting 5 ml of the media serially at each time point, from a volume of 400 ml culture of each strain. The pH-time curves (Fig. 1) demonstrate that the JS32 sorbitol fermentation medium pH dropped gradually over time, while that of N16961 leveled off at pH 6.5 for about 2 hours before dropping again. The change in pH was consistent with the sorbitol fermentation test, showing that nonOSI-744 mouse toxigenic buy Paclitaxel strains display positive results earlier than toxigenic strains . Figure 1 pH-time curves of toxigenic strain N16961 and nontoxigenic strain JS32 on sorbitol
fermentation media. 1H-NMR analysis In order to understand the differences in pH observed for the toxigenic and nontoxigenic strains, we examined changes in medium components using 1H-NMR. The majority of the components in the sorbitol fermentation media exhibited similar depletion or formation for JS32 and N16961 (Fig. 2). One exception was the appearance of two volatile aminophylline compounds (formate and lactic acid). Formate appeared in the JS32 culture earlier than in the N16961 culture, and the different production rates of formate between these two V. cholerae
strains were consistent with their pH changes and fermentation rates. At the time of color change in the JS32 fermentation sample, the concentrations of acetic acid and formate in the medium were 30.53 mg/L and 16.86 mg/L (0.509 mmol/L and 0.367 mmol/L, respectively). In contrast, the acetic acid concentration in N16961 fermentation media was 24.37 mg/L (0.406 mmol/L), and formate was below the level of detection. Figure 2 1 H-NMR spectra of JS32 and N16961 sorbitol fermentation medium. Samples were collected at four time points: the starting time (0 h), the JS32 color change (4 h), the N16961 color change (8 h), and 24 hours. Formate could be seen at 4 h in JS32, while there was no formate peak in N16961.