Inhibition of nitrifiers and methanotrophs from an agricultural humisol byallylsulfide and its implications for environmental studies

Allylsulfide, an inhibitor of ammonia monooxygenase, was tested to determin e its ability to inhibit nitrification and methane oxidation in pure cultur es, in agricultural humisol enrichment cultures, and in humisol slurries, W e confirmed that allylsulfide is a differential inhibitor of cultures of ni trifiers and methanotrophs at concentrations of 1 and 200 mu M, respectivel y, which result in 50% inhibition. However, although a nitrifying enrichmen t culture added to sterilized humisol was inhibited 50% by 4 mu M allylsulf ide, 500 mu M allylsulfide was necessary for 50% inhibition of the endogeno us nitrifying activity in nonsterile humisol, We concluded that native nitr ifiers were protected, possibly by being in colonial aggregates or sheltere d microenvironments.