Different Dissolved Oxygen Research Articles

Physiological response mechanisms of hybrid Pelteobagrus fulvidraco in response to different dissolved oxygen

In order to study the physiological responses of hybrid Pelteobagrus fulvidraco (Pelteobagrus fulvidraco ♀ × Pelteobagrus vachelli ♂) under different dissolved oxygen (DO), the experiment analysed and compared the changes in growth, oxidative stress, apoptosis, and intestinal microorganisms of hybrid P. fulvidraco exposed to DO in group L (DO = 6.0 ± 1 mg/L), group M (DO = 9.0 ± 1 mg/L, as a control group in this study) and group H (DO = 12.0 ± 1 mg/L) for 7 days, 14 days, and 14 days of restoration of DO. The results showed that the growth were inhibited in groups L and H, and the activities of antioxidant enzymes (superoxide dismutase, catalase, malondialdehyde, and glutathione) in gill and liver were differently altered in group L and H compared to group M. It was found that there was fusion of gill lamellae in group H, and there was basal proliferation in group L. At the same time, both H and L groups exhibited inflammatory reactions, cell necrosis, and vacuoles in liver. Morphometric analysis showed that groups H and L exacerbated gill apoptosis, while the liver showed no significant changes among different treatments. After different DO treatments, a significant decrease in the diversity and richness of intestinal microorganisms in the H and L groups compare to M group. After 14 days of treatment with oxygen concentration restored to 9 mg/L, oxidative stress, gill and liver damage were alleviated, and the diversity and richness of intestinal microorganisms significantly increased. In addition, the contribution of water column microorganisms to intestinal microorganisms was elevated to 20.1% with increasing oxygen concentrations. These results suggest that DO fluctuation affects the physiological functions of hybrid P. fulvidraco and negatively affects the healthy culture of the fish.

Electrochemical study on the fretting corrosion synergistic damage mechanism of 316L SS in different dissolved oxygen solution

Nowadays, material aging issues in the nuclear industry have received wide attention as they need costly maintenance strategies to deal with. Therefore, it is important to study the degradation mechanism of materials to improve their service life. In this study, in-situ electrochemical measurement techniques were used to investigate the fretting corrosion synergistic damage mechanism of 316L SS tube against zirconia ceramics plate in the solution with different dissolved oxygen (DO) concentrations. The results show that a more uniform passive film with the main composition of corundum oxides γ-Fe2O3 and oxyhydroxide γ-FeOOH formed on the wear scar under higher DO concentration, which hindered the charge transfer and improved corrosion resistance. The passive film modifies contact pressure and changes wear behavior, resulting in a 55.5 % reduction in the fretting corrosion damage. The main damage mechanism changes from abrasive wear to a mixing mechanism of surface fatigue and abrasive wear. The contribution of the synergistic damage effect was quantified, which is the key part of fretting corrosion damage and weakens with the increase of DO concentration. According to the experimental results, a prediction model of corrosion-induced wear damage was proposed based on the Archard equation, Hertz contact theory, and passive film coverage model.

Simultaneous nitrification and denitrification of real domestic wastewater using novel biodegradable Cocos Nucifera fibre as biofilter media and carbon source: Performances and microbial community composition

The simultaneous nitrification and denitrification (SND) performances in biofiltration system are largely governed by the filter media material and also the operating conditions. Moreover, a significant gap exists regarding the influence of different operating conditions on the SND performances in using plant-based waste materials as the biofilter media. Thus, in this study, long-term SND and organic pollutants removal were investigated in a continuous-flow biofiltration system filled with novel biodegradable Cocos nucifera fibre media operating under different dissolved oxygen (DO) concentrations, HRT and backwash intensity. Under best operating conditions of DO 1.5 mg/L, HRT 16.0 h, and airflow and water flow rate of 1.0 L/m2/s, the biofiltration system was able to remove an average of 70.7 % of NH3-N, 98.5 % of NO2-N, 90.3 % of COD, 86.9 % of soluble COD (sCOD), 98.7 % of TSS, 70.4 % of TN and achieved 94.3 % of SND efficiencies. The coexistence of enriched functional microorganisms such as nitrifiers (Nitrosomonas, Nitrospira) and denitrifiers (Dechloromonas, Zoogloea, Acidovorax) were believed to be responsible for the efficient performance of the system working under best operating conditions.

Electrochemical study on the fretting corrosion synergistic damage mechanism of Inconel 690 alloy in different dissolved oxygen solution

In-situ electrochemical measurement was used to investigate the fretting corrosion synergistic damage mechanism of Inconel 690 alloy in the solution with different dissolved oxygen (DO) concentrations. The synergistic mechanism of fretting corrosion was quantified. Results show that the minimum fretting corrosion damage of Inconel 690 was obtained at DO concentration of 2 ppm and the corrosion-accelerated wear, which can be represented by the influence of third body layer (TBL) on the fretting corrosion damage mechanism, is the key contributor. The formation and rupture of TBL have been observed under different DO concentrations. In transitional stages of TBL formation and the stage where uniform morphology formed, the TBL with excellent ductility can improve the contact behavior and reduce fretting corrosion damage. In stages during which TBL breaks into hard spinel oxides, severe abrasive wear and fretting corrosion damage will be caused.

Nitrogen removal from dewatering liquid of landfill sludge by partial nitrification and denitrification

Two pilot-scale two-stage anoxic/oxic membrane bioreactors were operated at different dissolved oxygen (DO) levels to evaluate nitrogen removal performances for treating landfill sludge dewatering liquid. Under either high (5.0–6.0 mg/L) or conventional DO (2.0–3.0 mg/L) conditions, partial nitrification (PN)-denitrification was both achieved, and high-concentration free ammonia (FA) ensured stable PN. The high DO system exhibited higher nitrite accumulation (98.5 %) and nitrogen removal (98.0 %), and its nitrogen removal was mainly ascribed to PN-denitrification (53.8 %). Kinetic inhibition tests and microbial sequencing results demonstrated that high DO condition improved the abundance and ability of ammonia-oxidizing bacteria (AOB) rather than nitrite-oxidizing bacteria under the FA inhibition. Pseudomonas, Thauera, and Soehngenia were characteristic genus in the high DO system, and Nitrosomonas was only AOB. Metagenomic analysis confirmed the important role of PN on nitrogen removal in high DO system. This provides valuable references for the efficient and economic treatment of ammonia-rich wastewater.

Modelling greenhouse gas emissions from biological wastewater treatment by GPS-X: The full-scale case study of Corleone (Italy)

Greenhouse gas (GHG) emissions from wastewater treatment plants (WWTPs) can affect climate change and must be measured and reduced. Mathematical modelling is an attractive solution to get a tool for GHG mitigation. However, although many efforts have been made to create reliable tools that can simulate “sustainable” full-scale WWTP operation, these studies are not considered complete enough to include GHG emissions and energy consumption of biological processes under long-term dynamic conditions. In this study, activated sludge model no. 1 (ASM1) was modified to model nitrous oxide (N2O) emissions with a plant-wide modelling approach. The model is novel compared to the state of the art since it includes three steps denitrification, all N2O production pathways and its stripping in an ASM1. The model has been calibrated and validated through long-term water quality and short-term N2O emissions data collected from Corleone (Italy) WWTP. Different dissolved oxygen (DO) concentrations and return sludge (RAS) ratios were tested with dynamic simulations to optimise the full-scale WWTP. The scenarios have been compared synergistically with effluent quality, direct GHG emissions, and energy footprint by the water-energy‑carbon coupling index (WECCI). This modelling study is novel as it fully covers long-term calibration/validation of the model with N2O measurements and tests the dynamic optimisation. Decision-makers and operators can use this new model to optimise GHG emissions and treatment costs.

Gut flora alterations among aquatic firefly Aquatica leii inhabiting various dissolved oxygen in fresh water

Knowledge about the impact of different dissolved oxygen (DO) on the composition and function of gut bacteria of aquatic insects is largely unknown. Herein, we constructed freshwater environments with different DOs (hypoxia: 2.50± 0.50, normoxia: 7.00± 0.50, and hyperoxia: 13.00± 0.50mg/L) where aquatic firefly Aquatica leii larvae lived for three months. Their gut flora was analyzed using the combination of 16S rRNA amplicon sequencing and metagenomics. The results showed no difference in alpha diversity of the gut flora between A.leii inhabiting various DOs. However, the relative abundance of several bacterial lineages presented significant changes, such as Pseudomonas. In addition, bacterial genes with an altered relative abundance in response to various DOs were primarily related to metabolism. The alteration of these functions correlated with the DO change. This is the first to uncover structure of gut flora under various DOs in aquatic insect larvae.

Impact of Influent Composition and Operating Conditions on Carbon and Nitrogen Removal from Urban Wastewater in a Continuous-Upflow (Micro)Aerobic Granular Sludge Blanket Reactor

Aerobic granular sludge is an interesting alternative to the conventional activated sludge (CAS) system and modified-Ludzack–Ettinger (MLE) process for biological wastewater treatment, as it allows a more cost-effective and simultaneous removal of carbon (C) and nitrogen (N) compounds in a single stage. In this study, (micro)aerobic C and N removal from synthetic urban wastewater was investigated in a continuous-double-column-upflow aerobic granular sludge blanket (UAGSB) system. The UAGSB reactor was operated under different dissolved oxygen (DO) ranges (0.01–6.00 mg∙L−1), feed C/N ratios (4.7–13.6), and hydraulic retention times (HRTs) (6–24 h). At a DO range of 0.01–0.30 mg∙L−1, feed C/N ratio of 13.6, and HRT of 24 h, the UAGSB achieved the highest chemical oxygen demand (COD), N-NH4+, and total inorganic nitrogen (TIN) removal efficiencies of 86, 99, and 84%, respectively. A preliminary assessment of the energy and economic savings associated with the process investigated was also carried out. The impact of capital and operating costs mainly related to the energy consumption of the aeration was taken into account. The assessment reveals that the capital and energy expenses of the UAGSB reactor would result in cost savings of around 14 and 7%, respectively, compared with a MLE system.

Partial Nitrification Characteristics of an Immobilized Carrier in Municipal Wastewater under Low-Temperature Shock: The Role of the Nitrifying Bacterial Community Structure

To analyze the effects of the nitrifying bacterial community structure on the partial nitrification (PN) characteristics in a PN-immobilized carrier in municipal wastewater under low-temperature shock, two PN-immobilized carriers with different nitrifying bacterial communities were investigated. The E1-immobilized carrier contained a high abundance of ammonia-oxidizing bacteria (AOB; 38.59%), and the E2-immobilized carrier had a low AOB abundance of 4.78%. The results of experiments with different dissolved oxygen (DO) concentrations showed that the oxygen-limited environment inside the immobilized carrier, generated by the high AOB abundance, was critical for achieving PN. The nitrite accumulation rate (NAR) decreased from 90.0–93.9% to 84.2–88.3% for the E1-immobilized carrier and from 86.0–90.4% to 81.7–85.8% for the E2-immobilized carrier under low-temperature shock (the temperature suddenly decreased from 25 ± 1 °C to 15 ± 1 °C). The decrease in the ammonia oxidation rate due to the decreased AOB activity led to a decrease in NAR. Moreover, NOB abundance in the E2-immobilized carrier increased because of the destruction of the oxygen-limiting region in the immobilized carrier due to the low AOB abundance. Increasing the abundance of AOB in the PN-immobilized carrier could reduce the adverse effects from the low-temperature shock. The results of this study can be used to further develop immobilization technology for efficient PN in mainstream wastewater treatment.

Dissolved oxygen alters the microbial interactions of anammox consortia in PN/A process

The main purposes of this study were to investigate the effects of different dissolved oxygen (DO) conditions (0.3 and 1.0 mg/L) on the microbial interactions in the partial nitrification/anammox (PN/A) process. The results indicated that the high concentration of DO (1.0 mg/L) significantly inhibited the activity of anammox bacteria (AnAOB) while enhanced the activity of nitrite oxidation bacteria (NOB) in the PN/A reactor. 1.0 mg/L DO promoted the abundance of NOB (such as Nitrospira) and some heterotrophic microorganisms (e.g., SBR1031 and OLB13), while decreased ammonia oxidizing bacteria (AOB, e.g., Nitrosomonas) and AnAOB (Ca.Brocadia and Ca.Kuenenia). 1.0 mg/L DO concentration driven a larger and more complex network with increased percentage of positive links, which might be a strategy for microbes to resist the adverse environment. Furthermore, the subnetworks of anammox bacteria and Nitrosomonas became smaller and simpler, whilst the subnetworks of heterotrophic bacteria (SBR1031) were more complex and connected. The decreased activity and abundance of AnAOB, together with the shifts of microbial interactions might result in the deterioration of nitrogen removal under 1.0 mg/L DO. This study provides a relatively comprehensive perspective for us to understand the effects of DO on the microbial interactions in the PN/A system.

Effect of External Aeration on Cr (VI) Reduction in the Leersia hexandra Swartz Constructed Wetland-Microbial Fuel Cell System

Cr (VI) is hazardous to humans and our environment. Leersia hexandra Swartz (L. hexandra) is the first wet chromium hyperaccumulator found in China. This study constructed the L. hexandra constructed wetland-microbial fuel cell (CW-MFC) system to treat Cr (VI) wastewater. It also determined the effects of different dissolved oxygen (DO) concentrations on power generation, pollutant removal, and Cr (VI) reduction. Cathode aeration promoted the voltage output and pollutant removal of the L. hexandra CW-MFC when the DO concentration was 4.5 mg·L−1: the highest voltage was 520 mV, the chemical oxygen demand (COD) removal rate was 93.73%, and the Cr (VI) removal rate was 97.77%. Moreover, the increase in the DO concentration improved the absorption of heavy metal Cr by the substrate and L. hexandra, and promoted the transformation from Cr (VI) to Cr (III). Chromium mostly exists as a residue with low toxicity and low mobility in L. hexandra and the substrate. This proves that the increased DO concentration promotes the redox reaction in the system and plants, reducing Cr (VI) to Cr (III). At the same time, the key micro-organism Geobacter that enhances the performance of the system and Cr (VI) reduction was found. The research results can provide a reference for the subsequent CW-MFC treatment of actual Cr-containing wastewater.

Biotechnological Production of Optically Pure 2,3-Butanediol by Bacillus subtilis Based on Dissolved Oxygen Control Strategy

2,3-Butanediol (2,3-BD) is a promising platform chemical, produced from microbial cells. Oxygen availability is a crucial factor driving the formation and proportion of 2,3-BD and acetoin in 2,3-BD producing bacterial strains. In this study, the ability of B. subtills GD5 to produce 2,3-BD in optimized sucrose-based media was evaluated, by investigating the impact of carbon to nitrogen (C/N) ratio and the effectiveness of alternative low-cost nitrogen sources (corn steep liquor, soybean meal, and ammonium sulphate). Subsequently, different dissolved oxygen (DO) controlling regimes were assessed in batch bioreactor fermentations. The best fermentation outcomes were obtained with uncontrolled DO, achieving 5.88 g/L of optically pure (R,R)-2,3-BD (~100% purity), accompanied by a production yield of 0.43 g/g, and a productivity of 0.2 g/L/h. Additionally, the influence of the DO controlling regime on B. subtills key enzymes involved in the reverse activity of acetoin reductase was also monitored. A fed-batch process under the most suitable DO conditions was carried out to improve 2,3-BD production, achieving 42.31 g/L 2,3-BD with a production yield of 0.52 g/g. Thus, B. subtilis GD5 is a promising strain for the efficient production of pure chiral (R,R)-2,3-BD under uncontrolled DO conditions, using alternative low-cost nitrogen sources.

Effect of dissolved oxygen on high C/N wastewater treatment in moving bed biofilm reactors based on heterotrophic nitrification and aerobic denitrification: Nitrogen removal performance and potential mechanisms

In this study, it was investigated the nitrogen removal (NR) performance and potential mechanism for high C/N wastewater treatment under different dissolved oxygen (DO) concentrations. The results showed that DO concentration significantly affected the removal efficiency of total nitrogen (TN). When the initial DO increased from 0.5 to 1.5 mg/L, TN removal efficiency significantly increased from 65 % to 85 %. However, a further DO increase did not promote TN removal, and the NR was only 80 % with an initial DO concentration of 3.5 mg/L. The effect of DO concentration on NR was influenced by the combined action of functional bacteria and electron flow. Excessive DO concentration did not positively affect NR efficiency but promoted electron utilization and respiratory proliferation. When the DO concentration was 1.5 mg/L, more electrons generated by sodium acetate metabolism were transferred to the aerobic denitrification process, compared to when the DO concentration was 3.5 mg/L.

Modeling and simulation of the biological process for treating wastewater with a low COD:N ratio under different dissolved oxygen conditions using an extended ASM2d model

Studies are currently lacking on the reaction mechanism of bacterial biopolymers (extracellular polymeric substances (EPS) and soluble microbial products (SMP)) for biological nutrient removal (BNR) in the activated sludge model No. 2d (ASM2d). Meanwhile, the relationship between biopolymers and BNR under different dissolved oxygen (DO) conditions is not completely clear. Thus, this work presented a modified ASM2d model that combines EPS and SMP (E-S-ASM2d), described in detail the interaction between the different bacteria and biopolymer dynamics in an anaerobic, anoxic, microaerobic and oxic (AAMO) reactor, and simulated the influences of DO on BNR process in low COD:N wastewater and on bacterial biopolymers. In addition, 16S rRNA gene analysis was used to characterize the microbial community dynamics in the AAMO reactor under different DO conditions, thus verifying the necessity of introducing microbial interactions to the E-S-ASM2d model. According to the measurements, the average total nitrogen removal rate of effluent increased 19.4 %, and the average EPS content increased 15.5 % under low DO. According to sensitivity analysis, high sensitivity parameters vary under different DO concentrations (namely 3 mg L−1 and 0.5 mg L−1 DO), which demonstrates the need to determine and separately calibrate these parameters according to DO. Finally, compared with traditional ASM2d model, the correlation likelihood values of E-S-ASM2d model for COD, ammonia nitrogen, total nitrogen and total phosphorus of AAMO effluent increased from 0.622, 0.704, 0.639 and 0.329 to 0.850, 0.894, 0.909 and 0.897, respectively, indicating E-S-ASM2d can significantly improve the simulation of nutrient removal under low influent COD:N.

A comparative evaluation of the sustainability of alternative aeration strategies in biological wastewater treatment to support net-zero future

In the plight for sustainable development and to support net zero ambitions for climate change mitigation, a broad range of aeration strategies have been developed with the hope of improving efficiency to minimize environmental and economic costs associated with the wastewater treatment processes. However, a balance is levied between reducing oxygen availability and hindering aerobic processes thus compromising performance. In the present work, we evaluate and compare the sustainability of a range of investigated strategies including continuous aeration (CA) at different dissolved oxygen (DO) setpoints (0.5 mg/L, 2.5 mg/L, 4.5 mg/L) and intermittent aeration (IA) at different oxic-anoxic portions (2.5 h on/0.5 h off, 2.0 h on/1.0 h off, 1.5 h on/1.0 h off). To achieve this, an eco-efficiency assessment is performed based on the results of previous life cycle impact and costing analyses for each strategy, while also incorporating a third factor to account for their respective treatment performance. The results demonstrate a clear pattern of increased sustainability for the IA strategies (0.54–0.56 Pt/m3), compared to the CA strategies (0.76–0.77 Pt/m3). While only negligible difference was observed within each aeration type, the trade-off between environmental and economic efficiency and treatment performance was distinct in CA strategies. At the individual pollutant level, IA strategies demonstrated decreasing sustainability for total phosphorous (TP) removal as the anoxic cycle portion increased, while CA at 0.5 mg/L was shown to be the most sustainable strategy for the removal of this pollutant (0.61 Pt/m3). Further work is suggested to incorporate the relative N2O emissions generated by each strategy and to investigate other strategies based on automated control.

Higher dissolved oxygen levels promote downward migration of phosphorus in the sediment profile: Implications for lake restoration.

Lake restoration (typically sediment dredging) commonly involves producing a new sediment-water interface (SWI). This study comprehensively investigated the migration and transformation of P during the formation of a new SWI under different dissolved oxygen (DO) levels in the overlying water, based on Fe/Al-rich sediment. The results suggest that DO had a profound effect on the 0-7cm sediment layer properties and higher DO levels in the overlying water resulted in the diffusion of DO deeper into the sediments. Importantly, besides preventing Fe reductive dissolution and sulfides competition, higher DO levels inhibited the release of P from sediment by inducing the mitigation of P from the upper (0-3cm) into the bottom (3-7cm) sediments. The migration of P was found to be closely related to the interactions between organic matter and Al, Fe, and Ca in the sediment profile caused by higher DO levels in overlying water. Particularly, the decrease in organic matter in the upper sediments increased the mobility of Ca and promoted aging of Al and Fe, which increased the migration of the different forms of P. The increased organic matter in the bottom sediments retained the mobile Ca and increased amorphous Fe, which immobilized the P that had migrated from the upper sediments. These results demonstrate the relatively high mobility of P in the upper sediments and the importance of P immobilization capability of bottom sediments on regulating P release from SWI under higher DO levels in overlying water. Accordingly, measures for lake restoration with producing a new SWI were recommended to be applied in combination with P immobilization method to develop more feasible strategies.

Corrosion behavior of T91 steel in liquid lead-bismuth eutectic at 550 °C: Effects of exposure time and dissolved oxygen concentration

Long-term corrosion behavior of T91 steel was investigated in 550 °C static liquid lead-bismuth eutectic (LBE) at different dissolved oxygen (DO) concentration. It was found that the oxide film formed in the oxygen-saturated LBE consists of iron-lead composite oxide, Fe3O4, Fe-Cr spinel and an inner oxidation zone (IOZ). The IOZ is composed of matrix and FeCr2O4 which follows orientation relationships with the matrix. The thickness of oxide film significantly reduces at DO= 1.26 × 10−6 wt %. Dissolution corrosion and intergranular penetration of Pb-Bi were observed at DO≤ 1.41 × 10−8 wt %. The corrosion mechanism of T91 steel in liquid LBE is discussed.

Hyaluronic acid production is enhanced by harnessing the heme-induced respiration in recombinant Lactococcus lactis cultures

Lactococcus lactis is a promising host for pathway-engineered production of high molecular weight hyaluronic acid (HA). This work investigates the effect of hemin-supplemented respiratory metabolism in an engineered L. lactis ldh mutant strain (Δldh L. lactis) as a strategy to enhance HA titer in the batch fermentation process. L. lactis lacks a functional electron transport chain (ETC) and ultimately relies on substrate-level phosphorylation for energy production. We conducted detailed investigations under different dissolved oxygen (DO) conditions and found a steady increase in HA titer with increased DO levels. We found a strong correlation between cofactor availability (NAD+ and acetyl-CoA) and the intracellular concentration of HA precursors, UDP-GlcUA and UDP-GlcNAc. We correlated the intracellular precursor levels with the HA titer obtained for the four conditions. We found that these were higher in hemin-supplemented cultures, with the best HA titer of 4.6 g/l. Finally, we observed that the molecular weight of HA (MWHA) correlates strongly with the ratio of HA precursors concentrations. We also found an inverse correlation between MWHA and HA titer across these experiments. These results can be used in optimizing the trade-off between molecular weight and HA production in bioprocesses involving recombinant L. lactis cultures.

Influence of Dissolved Oxygen Level on Chitin-Glucan Complex and Mannans Production by the Yeast Pichia pastoris.

The yeast Pichia pastoris was cultivated under different dissolved oxygen (DO) levels (5, 15, 30 and 50% of the air saturation) to evaluate its impact on the production of the cell-wall polysaccharide chitin–glucan complex (CGC) and mannans. Decreasing the DO level from 50 to 15% had no significant impact on cell growth but substrate conversion into biomass was improved. Under such conditions, a mannans content in the biomass of 22 wt% was reached, while the CGC content in the biomass was improved from 15 to 18 wt%, confirming that the DO level also impacted on P. pastoris cell-wall composition. Overall mannans and CGC volumetric productivity values of 10.69 and 8.67 g/(L. day) were reached, respectively. On the other hand, the polymers’ composition was not significantly affected by decreasing the DO level. These results demonstrated that considerable energy savings can be made in the polysaccharide production process by reducing the DO level during cultivation of P. pastoris by improving the overall polymers’ productivity without altering their composition. This has impact on the polysaccharide production costs, which is of considerable relevance for process scale-up and products’ commercialization.

The PhoPR two-component system responds to oxygen deficiency and regulates the pathways for energy supply in Corynebacterium glutamicum.

The PhoPR two-component system, a highly conserved system in corynebacteria and mycobacteria, is involved in the cellular response to environmental stress. When analysing the transcriptomic data of Corynebacterium glutamicum strains under different dissolved oxygen (DO) levels, PhoPR was found to be the most responsive two-component system to DO changes. Here, we systematically investigated the expression of PhoPR in response to different DO levels and its impact on genes related to global regulation and energy metabolism. Using Green fluorescent protein as a reporter, we confirmed that PhoPR was significantly upregulated upon decrease of DO. Through real-time quantitative PCR and electrophoretic mobility shift assay, we found that the effector protein PhoP directly activated glxR (encoding a global regulator), pfk and gapA (encoding the glycolytic enzymes) and ctaD (encoding cytochrome c in the electron transport chain), while downregulated aceE and gltA (encoding the TCA cycle enzymes). Overexpression of phoP or phoR resulted in a decreased intracellular NAD+/NADH ratio and increased intracellular ATP level, consistent with the gene expression changes regulated by PhoP. These results reveal the PhoPR system respond to oxygen deficiency and is responsible for the regulation of pathways involved in the sustainability of the energy levels required under low oxygen conditions. Our findings in this study not only provide new insights into the adaptation pathways of C. glutamicum in response to low oxygen conditions but also identify new possible genetic targets for the construction of the new cell factories aimed toward industrial applications.