A previous study showed that ammonia oxidation by the Thaumarchaeota Nitrosopumilus maritimus (group 1.1a) was resistant
to concentrations of the C₈ 1-alkyne, octyne, which completely inhibits activity by ammonia-oxidizing bacteria. In this study, the
inhibitory effects of octyne and other C₂ to C₁₀ 1-alkynes were evaluated on the nitrite production activity of two pure culture
isolates from Thaumarchaeota group 1.1b, Nitrososphaera viennensis strain EN76 and Nitrososphaera gargensis. Both N. viennensis
and N. gargensis were insensitive to concentrations of octyne that cause complete and irreversible inactivation of nitrite
production by ammonia-oxidizing bacteria. However, octyne concentrations (≥20 μM) that did not inhibit N. maritimus partially
inhibited nitrite production in N. viennensis and N. gargensis in a manner that did not show the characteristics of irreversible
inactivation. In contrast to previous studies with an ammonia-oxidizing bacterium, Nitrosomonas europaea, octyne inhibition
of N. viennensis was: (i) fully and immediately reversible, (ii) not competitive with NH₄⁺, and (iii) without effect on the
competitive interaction between NH₄⁺ and acetylene. Both N. viennensis and N. gargensis demonstrated the same overall trend
in regard to 1-alkyne inhibition as previously observed for N. maritimus, being highly sensitive to ≤C₅ alkynes and more resistant
to longer-chain length alkynes. Reproducible differences were observed among N. maritimus, N. viennensis, and N. gargensis
in regard to the extent of their resistance/sensitivity to C₆ and C₇ 1-alkynes, which may indicate differences in the ammonia
monooxygenase binding and catalytic site(s) among the Thaumarchaeota
