VjbR and C12-HSL modulate gene transcription in a temporal manner Comparison of altered gene transcripts resulting from the ΔvjbR mutation
revealed that 13% (54 statistically significant genes) were found to be regulated at both growth phases, suggesting that VjbR exerts temporal control over gene regulation (Additional File 3, Table S3). A similar subset of genes were also identified in wildtype bacteria that were treated with C12-HSL when compared to those without treatment, with 12% (54 genes, Additional File 3, Selleckchem Sirolimus Table S3) of transcripts altered at both growth stages. The low correlation of genes altered at both growth stages suggests that both VjbR and C12-HSL regulate distinct regulons at the two growth stages examined. A recent study compared microarray and proteomic data from a ΔvjbR mutant at a late exponential growth phase (OD600 = 0.75), corresponding to a total of 14 genes and the virB operon found at the growth phases examined here . Of the 14 genes in common with the study by Uzureau et al.; 2 genes and the virB operon identified in our
study (BMEI1435 and I1939) correlated in the magnitude of change with both the protein and microarray data, BMEI1267 correlated with the protein data, and 3 genes (BMEI1900, II0358 and II0374) correlated with the microarray data (Additional File 3, Table S3) . Additionally, 5 genes did not correspond with the magnitude of alteration in the microarray analyses conducted in this study (BMEI0747, I1305, Cepharanthine I1367, II0098 and II0923; Table 3 and Additional File learn more 3, Table S3) . The low similarity of regulated genes from these two studies that examined a total of 3 different
growth phases provides further support of the VjbR temporal gene regulation observed here . A similar pattern of temporal gene regulation by AHL quorum sensing signals has also been observed in P. aeruginosa [26, 40]. Distinct regulons were identified at an exponential and early stationary growth phase by utilization of a mutated strain that does not produce AHL signals, leading to the conclusion that the temporal regulation is independent of AHL concentration [26, 40]. Examination of two luxR gene transcript levels in P. aeruginosa revealed an increase from the late logarithmic to early stationary phase, coinciding with the induction of most quorum-activated genes and supporting a hypothesis that the receptor levels govern the onset of induction . Likewise, the relative expression of B. melitensis vjbR was found to increase 25-fold from exponential to stationary growth phase by qRT-PCR (Fig. 4). The observed increase in the transcript levels of vjbR supports a similar hypothesis for the temporal gene regulation observed by VjbR in B. melitensis Figure 4 Relative expression of vjbR transcript over time. Taqman real-time RT-PCR of vjbR in B.