Exploring the physiological link of breath N 2 O through nitrification and denitrification processes in human gastric juice

Abstract

Over the past several decades, it has been generally believed that microbial nitrification and denitrification are not significant processes in the human gastrointestinal tract. Moreover, the underlying physiological link between exhaled nitrous oxide (N 2 O) and aerobic denitrification in the gastric environment is still largely unknown. In this report, we provide direct experimental evidence of the aerobic denitrification process in the human gastrointestinal tract by evaluating concentrations of dissolved N 2 O and its precursor nitrite () ion in the gastric juice along with exhaled N 2 O concentration using a high-precision laser spectroscopy technique. Moreover, in vitro studies of gastric fluid in patients reveal a new mechanism of nitrification of ammonium ion () followed by denitrification of leading to the formation of N 2 O in the gastric environment, which is eventually excreted in exhaled breath. This observation was subsequently validated under in vivo physiological conditions exploiting the urease activity of the gastric pathogen Helicobacter pylori. Consequently, our findings established a strong physiological link between exhaled N 2 O and bacterial infection in the stomach. This deepens our understanding of the unusual microbial denitrification in the gastric environment, providing new insight into the activities of human-associated microorganisms, which eventually affect the human physiology and health.