Abstract
This study provides the first clear evidence that edible mushrooms, such as Lentinula edodes (shiitake), Pleurotus ostreatus and Pleurotus eryngii , can generate carbon monoxide (CO) as part of their metabolic activity—independent of bacteria, illumination or oxygen limitation. Systematic measurements of CO and CO 2 emissions were performed over 60 days using multiple fungal species, substrates and growth conditions. Microscopy observations (light, scanning and transmission electron microscopy) confirmed no extracellular and intracellular bacterial endosymbionts involved, supporting a fungal genesis of CO. CO emission patterns showed a parabola‐shaped curve, correlating with CO 2 levels regardless measurements by gas‐analyser or GC–MS and peaking during full mycelial colonisation. Shiitake mushrooms grown on birch substrate released the highest CO compared to alder and aspen substrates and P. ostreatus and P. eryngii . These findings suggest that fungal respiration contributes to CO dynamics more than previously recognised and highlight the need for further research into its mechanisms and environmental and occupational health implications.