Vitreoscilla hemoglobin promoter is not responsive to nitrosative and oxidative stress in Escherichia coli

The Vitreoscilla hemoglobin gene (vhb) is expressed under oxygen-limited conditions via an FNR-dependent mechanism. Furthermore, cAMP-CRP has been implicated in its regulation. Recently, VHb protein has been reported to protect a heterologous host from nitrosative stress. In this study we analyzed the regulation of the Vitreoscilla hemoglobin promoter (P_vhb) in Escherichia coli under nitrosative and oxidative stress conditions. Our results show unambiguously that expression of neither VHb nor chloramphenicol acetyltransferase under the control of P_vhb is induced under the experimental conditions used. Thus, a clear discrepancy between in vivo function, i.e. protection against nitrosative stress, and regulation of gene expression is obvious. The regulation of P_vhb reported here is in clear contrast to the expression pattern of flavohemoglobins from various microorganisms, which are generally induced by nitrosative stress. However, the length of P_vhb is only 146 bp and therefore, we cannot rule out that additional regulatory sequences may be located in the upstream region of P_vhb.