Improvement of Escherichia coli microaerobic oxygen metabolism by Vitreoscilla hemoglobin: New insights from NAD(P)H fluorescence and culture redox potential

Publisher Website
Google Scholar
Abstract
On‐line NAD(P)H fluorescence and culture redox potential (CRP) measurements were utilized to investigate the role of Vitreoscilla hemoglobin (VHb) in perturbing oxygen metabolism of microaerobic Escherichia coli Batch cultures of a VHb‐synthesizing E. coli strain and the iso‐genic control under fully aerated conditions were subject to several high/low oxygen transitions, and the NAD(P)H fluorescence and CRP were monitored during these passages. The presence of VHb decreased the rate of net NAD(P)H generation by 2.4‐fold under diminishing oxygen tension. In the absence of aeration, the strain producing VHb maintained a steady NAD(P)H level 1.8‐fold less than that of the control, indicating that the presence of VHb keeps E. coli in a more oxidized state under oxygen‐limited conditions. Estimated from CRP, the oxygen uptake rates near anoxia were 25% higher for cells with VHb than those without. These results suggest that VHb‐expressing cells have a higher microaerobic electron transport chain turnover rate. To examine how NAD(P)H utilization of VHb‐expressing cells responds to rapidly changing oxygen tension, which is common in large‐scale fermentations, we pulsed air intermittently into a cell suspension and recorded the fluorescence response to the imposed dissolved oxygen (DO) fluctuation. Relative to the control, cells containing VHb had a sluggish fluorescence response to sudden changes of oxygen tension, suggesting that VHb buffers intracellular redox perturbations caused by extracellular DO fluctuations.© John Wiley & Sons, Inc.