Effect
of CO<sub>2</sub> on Microbial Denitrification
via Inhibiting Electron Transport and Consumption
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Abstract
Increasing
anthropogenic CO<sub>2</sub> emissions have been reported
to influence global biogeochemical processes; however, in the literature
the effects of CO<sub>2</sub> on denitrification have mainly been
attributed to the changes it causes in environmental factors, while
the direct effects of CO<sub>2</sub> on denitrification remain unknown.
In this study, increasing CO<sub>2</sub> from 0 to 30 000 ppm
under constant environmental conditions decreased total nitrogen removal
efficiency from 97% to 54%, but increased N<sub>2</sub>O generation
by 240 fold. A subsequent mechanistic study revealed that CO<sub>2</sub> damaged the bacterial membrane and directly inhibited the transport
and consumption of intracellular electrons by causing intracellular
reactive nitrogen species (RNS) accumulation, suppressing the expression
of key electron transfer proteins (flavoprotein, succinate dehydrogenase,
and cytochrome c) and the synthesis and activity of key denitrifying
enzymes. Further study indicated that the inhibitory effects of CO<sub>2</sub> on the transport and consumption of electrons were caused
by the decrease of intracellular iron due to key iron transporters
(AfuA, FhuC, and FhuD) being down-regulated. Overall, this study suggests
that the direct effect of CO<sub>2</sub> on denitrifying microbes
via inhibition of intracellular electron transport and consumption
is an important reason for its negative influence on denitrification