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

Abstract

Allylsulfide, an inhibitor of ammonia monooxygenase, was tested to determine its ability to inhibit nitrification and methane oxidation in pure cultures, in agricultural humisol enrichment cultures, and in humisol slurries. We confirmed that allylsulfide is a differential inhibitor of cultures of nitrifiers and methanotrophs at concentrations of 1 and 200 microM, respectively, which result in 50% inhibition. However, although a nitrifying enrichment culture added to sterilized humisol was inhibited 50% by 4 microM allylsulfide, 500 microM allylsulfide was necessary for 50% inhibition of the endogenous nitrifying activity in nonsterile humisol. We concluded that native nitrifiers were protected, possibly by being in colonial aggregates or sheltered microenvironments.

FIG. 1

Allylsulfide inhibition of NH₄⁺ oxidation (solid symbols) and CH₄ oxidation (open symbols) by cultures used in this study.

FIG. 2

Acetylene inhibition of nitrification (NO₂⁻ and NO₃⁻ production) by humisol slurries. Acetylene pressures (in pascals) are indicated next to the lines. The data are averages ± standard errors of the means based on data from three flasks. Error bars that are not visible are smaller than the symbols.

FIG. 3

Effect of allylsulfide on activity of a nitrifier enrichment culture added to autoclaved humisol (measured by determining NO₂⁻ production in the presence of 10 mM KClO₃). The allylsulfide concentrations (micromolar) are indicated next to the lines. The data are averages ± standard errors of the means based on data from three flasks. Error bars that are not visible are smaller than the symbols. (Inset) Percent inhibition as a function of allylsulfide concentration.

FIG. 4

Effect of allylsulfide (AS) on blended humisol slurry nitrification (measured by determining NO₂⁻ production in the presence of 10 mM KClO₃). An unblended control (□) was included for comparison. The allylsulfide concentrations (micromolar) are indicated next to the lines. The NO₂⁻ production data are averages ± standard errors of the means based on data from three flasks. Error bars that are not visible are smaller than the symbols. (Inset) Percent inhibition of a blended slurry as a function of allylsulfide concentration.