Abstract
Understanding bacterial physiology relies on elucidating the regulatory mechanisms and cellular functions of those differentially expressed genes in response to environmental changes. A widespread Gram-negative bacterial outer membrane protein OmpW has been implicated in the adaptation to stresses in various species. It is recently found to be present in the regulon of the global anaerobic transcription factor FNR and ArcA in Escherichia coli. However, little is known about the physiological implications of this regulatory disposition. In this study, we demonstrate that transcription of ompW is indeed mediated by a series of global regulators involved in the anaerobiosis of E. coli. We show that FNR can both activate and repress the expression of ompW through its direct binding to two distinctive sites, -81.5 and -126.5 bp respectively, on ompW promoter. ArcA also participates in repression of ompW under anaerobic condition, but in an FNR dependent manner. Additionally, ompW is also subject to the regulation by CRP and NarL which senses the availability and types of carbon sources and respiration electron acceptors in the environment respectively, implying a role of OmpW in the carbon and energy metabolism of E. coli during its anaerobic adaptation. Molecular docking reveals that OmpW can bind fumarate, an alternative electron acceptor in anaerobic respiration, with sufficient affinity. Moreover, supplement of fumarate or succinate which belongs to the C4-dicarboxylates family of metabolite, to E. coli culture rescues OmpW-mediated colicin S4 killing. Taken together, we propose that OmpW is involved in anaerobic carbon and energy metabolism to mediate the transition from aerobic to anaerobic lifestyle in E. coli.
Highlights
Carbon and energy homeostasis is essential for bacterial physiology and survival in a constantly changing environment
To investigate whether Fumarate and Nitrate Reduction (FNR) directly binds to the promoter of ompW and activates its expression, we performed electro-mobility shift assay (EMSA) using the FNRD154A variant which exists as a functional dimer even under aerobic conditions (Lazazzera et al, 1993)
Ethidium bromide (EB) staining of the EMSA reactions revealed that FNR directly bound to the promoter region of ompW as a shifted band corresponding to the protein-DNA complex was observed upon the addition of FNRD154A protein (Figure 2B)
Summary
Carbon and energy homeostasis is essential for bacterial physiology and survival in a constantly changing environment Maintenance of this homeostasis is often achieved by coordinated regulatory networks that involve complex signal transduction pathways and gene expression changes. While the single component transcription regulator FNR directly senses the absence of molecular O2 in the cytoplasm of bacteria and activates the expression of genes important to the anaerobic lifestyle of the bacterial species, the two component system ArcAB senses the redox status in the cytoplasmic membrane of bacteria through its membrane sensor ArcB, and upon activated, primarily represses the expression of genes involved in the aerobic carbon oxidation through its cognate response regulator ArcA (Green and Paget, 2004; Fleischhacker and Kiley, 2011; Myers et al, 2013; Park et al, 2013). The cellular functions of OmpW and its physiological relevance to bacterial anaerobiosis are not known
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