Expression of Vitreoscilla hemoglobin is superior to horse heart myoglobin or yeast flavohemoglobin expression for enhancing Escherichia coli growth in a microaerobic bioreactor

Expression of a gene encoding hemoglobin (VHb) from the aerobic bacterium Vitreoscilla sp. in several organisms, including Escherichia coli, has been shown to improve microaerobic cell growth and enhance oxygen-dependent product formation. The suitability of VHb to enhance microaerobic metabolism has been suggested to depend on its unusual oxygen binding characteristics. To examine whether hemoproteins of other origins can also elicit the positive effects VHb exerts in microaerobic E. coli cells, we subcloned the genes encoding Vitreoscilla VHb, horse heart myoglobin (HMb), and yeast flavohemoglobin (YFb) behind the IPTG-inducible tac promoter on a medium-copy-number vector and transformed these globin-expression plasmids into E. coli MG1655 and DH5 alpha. Biologically active VHb, HMb, and YFb were produced from these constructions in E. coli as judged by their ability to abduct carbon monoxide. The presence of HMb increased the growth of wild-type cells during the early stages of fed-batch growth, but the final optical densities of HMb-expressing cultures were comparable with the wild-type control not synthesizing HMb. The presence of VHb increased the cell density by 70% under the same cultivation conditions. The expression of wild-type YFb reduced the final cell density by 30% relative to the non-globin-expressing control.