Effect of CO₂ on Microbial Denitrification via Inhibiting Electron Transport and Consumption

Abstract

Increasing anthropogenic CO2 emissions have been reported to influence global biogeochemical processes; however, in the literature the effects of CO2 on denitrification have mainly been attributed to the changes it causes in environmental factors, while the direct effects of CO2 on denitrification remain unknown. In this study, increasing CO2 from 0 to 30 000 ppm under constant environmental conditions decreased total nitrogen removal efficiency from 97% to 54%, but increased N2O generation by 240 fold. A subsequent mechanistic study revealed that CO2 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 CO2 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 CO2 on denitrifying microbes via inhibition of intracellular electron transport and consumption is an important reason for its negative influence on denitrification.

Direct and Indirect Effects of Increased CO2 Partial Pressure on the Bioenergetics of Syntrophic Propionate and Butyrate Conversion

“…At elevated pCO 2 , the equilibrium dissolved CO 2 concentration in the liquid medium increased from 320 to 8,620 mg L –1 ( Supporting Information , Table S5). These dissolved CO 2 concentrations are in line with values reported by Wan et al 10 (3,000–30,000 ppm), which negatively impacted the nitrogen removal efficiency because of increased membrane permeability, thus inhibiting electron transport and protein expression.…”

“…These authors proposed that elevated pCO 2 caused direct inhibition of the carbon metabolism, electron transport chain, enzymatic activity, and substrate consumption at the expense of increased buffer concentration to prevent a pH drop. 10 , 11 …”

Insights into simultaneous microbial chromium and nitrate reduction: inhibitory effects and molecular mechanisms

“…Finally, 2 mL methanol (96%) was added to extract the INF in the precipitates, which was measured spectrophotometrically at 490 nm. The ETSA was calculated according to the following equation: where ABS 490 is the sample absorbance, 15.9 is the specific absorptivity of INT−formazan, V 0 and V 1 are the initial volume of bacteria and the total volume of methanol (mL), respectively, t is the incubation time (min), and 32/2 is a constant for transformation of μmol INT‐formazan to μg O 2 .…”

The response of the marine nitrogen cycle to ocean acidification

“…No significant mean effect was detectable for either denitrification rates or nirS-transcript abundance which is indicative of denitrifier activity (−0.0185 ± 0.282 and −0.09 ± 0.25, respectively, Figure 1b, potential explanation for this is that OA induces damage to the bacterial membrane and directly inhibits transport and consumption of intracellular electrons. This leads to an accumulation of intracellular reactive nitrogen species (e.g., NO) that further suppress the expression of key electron transfer proteins, and the synthesis and activity of key denitrifying enzymes (Wan et al, 2016). Consequently, denitrification rates may decrease under OA from an energetic perspective, but no significant impact is detected in the meta-analysis.…”