Deciphering the Inhibition of Ethane on Anaerobic Ammonium Oxidation

Anaerobic ammonium oxidation (anammox) and nitrification,
two common
biological ammonium oxidation pathways, are critical for the microbial
nitrogen cycle. Short chain alkanes (C2–C8) have been well-known as inhibitors for nitrification through interaction
with the ammonia monooxygenase, while whether these alkanes affect
anammox is an open question. Here, this work demonstrated significant
inhibition of ethane on anammox and revealed the inhibitory mechanism.
The acute inhibition of ethane on anammox was concentration-dependent
and reversible; 0.86 mM dissolved ethane caused 50% inhibition (IC50), and 1.72 mM ethane almost completely inhibited anammox.
After long-term exposure to 0.09 mM ethane for 30 days, the ammonium
(nitrite) removal rate dropped from 202 (267) mg N L–1 d–1 to 1 (1) mg N L–1 d–1, and the abundance of anammox bacteria decreased
from 61.9% to 9.5%. The intercellular ammonium concentration of anammox
bacteria decreased after ethane exposure, while metatranscriptome
analysis showed significant upregulation of genes for ammonium transport
of anammox bacteria. Thus, ethane could suppress ammonium uptake resulting
in the inhibition of anammox activities. As ethane is the second most
prevalent alkane after methane in various anoxic environments, ethane
may have an important effect on the nitrogen cycle driven by anammox
that should be investigated in future research.