Bacterial Hemoglobins and Flavohemoglobins for Alleviation of Nitrosative Stress in <i>Escherichia coli</i>

<jats:title>ABSTRACT</jats:title> <jats:p> <jats:italic>Escherichia coli</jats:italic> MG1655 cells expressing novel bacterial hemoglobin and flavohemoglobin genes from a medium-copy-number plasmid were grown in shake flask cultures under nitrosative and oxidative stress. <jats:italic>E. coli</jats:italic> cells expressing these proteins display enhanced resistance against the NO <jats:sup>·</jats:sup> releaser sodium nitroprusside (SNP) relative to that of the control strain bearing the parental plasmid. Expression of bacterial hemoglobins originating from <jats:italic>Campylobacter jejuni</jats:italic> (CHb) and <jats:italic>Vitreoscilla</jats:italic> sp. (VHb) conferred resistance on SNP-challenged cells. In addition, it has been shown that NO <jats:sup>·</jats:sup> detoxification is also a common feature of flavohemoglobins originating from different taxonomic groups and can be transferred to a heterologous host. These observations have been confirmed in a specific in vitro NO <jats:sup>·</jats:sup> consumption assay. Protein extracts isolated from <jats:italic>E. coli</jats:italic> strains overexpressing flavohemoglobins consumed authentic NO <jats:sup>·</jats:sup> more readily than protein extracts from the wild-type strain. Oxidative challenge to the cells evoked nonuniform responses from the various cell cultures. Improved oxidative-stress-sustaining properties had also been observed when the flavohemoglobins from <jats:italic>E. coli</jats:italic> , <jats:italic>Klebsiella pneumoniae</jats:italic> , <jats:italic>Deinococcus radiodurans</jats:italic> , and <jats:italic>Pseudomonas aeruginosa</jats:italic> were expressed in <jats:italic>E. coli</jats:italic> . </jats:p>