Since the bacteriostatic effect of azide on gram-negative bacteria is well known (12), this compound is also likely to inhibit ammonia oxidizers. Azide was less effective in inhibiting ammonia oxidation than in inhibiting nitrite oxidation (Table 1 and Fig. 2); activity was inhibited 75% at concentrations of 2,800 and 0.8 μM with ammonia and nitrite oxidizers, respectively (Fig. 2). Thus, we assume that azide is a selective inhibitor of nitrite oxidation in a mixed bacterial population when the concentration is low (less than 24 μM).
Since allylthiourea (86 μM) and azide (24 μM) are selective, instantaneous, and effective inhibitors of ammonia and nitrite oxidizers respectively, a respirometric test that differentiates between endogenous respiration (by heterotrophs and/or nitrifiers) and exogenous heterotrophic and nitrifier respiration (by ammonia and nitrite oxidizers) within a mixed biomass may be described (Fig.3). The addition of a mixture of energetic substrates (ammonia, nitrite, and acetate) to a substrate-free biomass suspension leads to intense oxygen uptake, which is subsequently and selectively inhibited by allylthiourea (86 μM) and azide (24 μM) (Fig. 3).
Since the bacteriostatic effect of azide on gram-negative bacteria is well known (12), this compound is also likely to inhibit ammonia oxidizers. Azide was less effective in inhibiting ammonia oxidation than in inhibiting nitrite oxidation (Table 1 and Fig. 2); activity was inhibited 75% at concentrations of 2,800 and 0.8 μM with ammonia and nitrite oxidizers, respectively (Fig. 2). Thus, we assume that azide is a selective inhibitor of nitrite oxidation in a mixed bacterial population when the concentration is low (less than 24 μM).
Since allylthiourea (86 μM) and azide (24 μM) are selective, instantaneous, and effective inhibitors of ammonia and nitrite oxidizers respectively, a respirometric test that differentiates between endogenous respiration (by heterotrophs and/or nitrifiers) and exogenous heterotrophic and nitrifier respiration (by ammonia and nitrite oxidizers) within a mixed biomass may be described (Fig.3). The addition of a mixture of energetic substrates (ammonia, nitrite, and acetate) to a substrate-free biomass suspension leads to intense oxygen uptake, which is subsequently and selectively inhibited by allylthiourea (86 μM) and azide (24 μM) (Fig. 3).
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