Strain-dependent inhibition of nitrous oxide reduction in denitrifiers by yeast extract

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Abstract
Pseudomonas sp. type strain H8 (ATCC 35402) was shown to be capable of denitrification but unable to reduce N2O in a complex medium containing 0.15% yeast extract. When added to a defined medium, autoclaved or filter-sterilized yeast extract from various suppliers was confirmed to inhibit N2O reduction by H8. The inhibition increased to 90% when the yeast extract concentration was increased to 0.5% in the medium. Only one of seven other denitrifying pseudomonads tested was similarly inhibited. Fractionation of yeast extract on a Sephadex G-10 column showed that the component responsible was a small molecule (molecular weight 2+. Reduced glutathione was assayed in the first fraction of the Sephadex eluate and was found to mimic the effect of yeast extract. It is proposed that yeast extract inhibits N2O reduction by certain denitrifiers through glutathione complexing of Cu2+ which is a cofactor of N2O reductase.