Investigating the Amino Acid Induced Suppression of Nitric Oxide Detoxification in Escherichia coli

Abstract

Nitric oxide (NO•) plays an integral role in the host-pathogen relationship. Host immune cells generate NO• to prevent bacterial virulence, but pathogens have evolved NO• detoxification enzymes to thwart their effectiveness. One consequence of NO• stress for pathogens is the inability to synthesize amino acids, leading to inhibited growth. Previous studies demonstrated that the addition of amino acids to the extracellular media alleviated NO• mediated growth inhibition. We theorized that the presence of amino acids could also improve NO• detoxification through facilitating the production of relevant detoxification enzymes. Using Escherichia coli as our model bacteria, we discovered that amino acid supplementation instead inexplicably suppressed NO• detoxification. Experimental and computational approaches revealed that Hmp, the predominant aerobic NO• detoxification enzyme in E. coli, was not compromised in its catalytic ability, but its synthesis under NO• stress was inhibited by the inclusion of amino acids in the extracellular media. Quantification of mRNA production from the hmp promoter following NO• treatment suggested that a transcriptional defect caused by the presence of amino acids may be contributing to the inhibition of Hmp synthesis.