Carbon Source Availability Research Articles

Compartmentalized Sesquiterpenoid Biosynthesis and Functionalization in the Chlamydomonas reinhardtii Plastid.

Terpenoids play key roles in cellular metabolism and can have specialized functions. Their heterologous production in microbial hosts offers an alternative to natural extraction. Here, we developed a subcellular engineering approach in the model green alga Chlamydomonas reinhardtii by targeting both sesquiterpenoid synthases and cytochrome P450s (CYPs) to the plastid, exploiting its photosynthetic electron transport chain to drive CYP-mediated oxidation without reductase partners. Nuclear-encoded sesquiterpenoid synthases were expressed with farnesyl pyrophosphate synthase fusions and targeted to the plastid, while CYPs were modified for soluble localization in the plastid stroma by removing transmembrane domains. The plastid environment supported hydroxylation, epoxidation, and oxidation reactions, with functionalization efficiencies reaching 80% of accumulated products. Carbon source availability influenced product ratios, revealing metabolic flexibility in the engineered pathways. Overall sesquiterpenoid yields ranged between 250-2500 µg L-1 under screening conditions, establishing proof-of-concept for using plastid biochemistry in complex terpenoid biosynthesis. Living two-phase terpenoid extractions with different perfluorinated solvents revealed variable performances based on sesquiterpenoid functionalization and solvent type. This work demonstrates that photosynthetic electron transport can drive CYP-mediated functionalization in engineered subcellular compartments. However, improvements in photobioreactor cultivation concepts will be required to facilitate the use of algal chassis for scaled production.

Carbon Carriers Driving the Net-Zero Future: The Role of Torrefied Biomass Pellets in Power-To-X

The latest Intergovernmental Panel on Climate Change Sixth Assessment Report urgently calls for sweeping action to mitigate the unprecedented impacts of climate change. The path to a carbon-neutral future is intricate, necessitating a multi-faceted approach that integrates decarbonization, defossilization, and energy/resource efficiency. Power-to-X (PtX) stands as a technological linchpin, converting renewable electricity into a range of sustainable products, from fuels to chemicals. However, its full potential is intrinsically tied to the availability of sustainable carbon sources. This paper evaluates the various avenues for carbon sourcing for PtX: direct air capture (DAC), biogenic carbon, and Long-cycle Industrial Carbon. DAC, although promising for the long term, has limitations in scalability and land requirements. Industrial long-cycle carbon capture technology is improving but requires a thorough Life Cycle Assessment for evaluating its sustainability. This study examines the environmental impacts, scalability, and logistical considerations of each carbon source. Biogenic carbon offers a near-term solution, and its various forms could simplify transportation logistics. An analysis of gasification processes, syngas cleaning, and hydrogen integration was conducted to assess the technical viability of these carbon sources in PtX applications. The results show that torrefied biomass pellets, after a thorough technical assessment, present a globally feasible and sustainable carbon carrier, setting the stage for industry standardization and easier global transportation. Syngas produced through the gasification of the pellets complemented by green hydrogen can be utilized in Fischer–Tropsch, methanol synthesis, and methanation, allowing PtX to synthesize practically any type of organic compounds in a hybrid Biomass–PtX (HBPtX) process. This study provides key insights for industries and policymakers by demonstrating the technical feasibility and sustainability of torrefied biomass as a carbon carrier, thereby supporting the development of comprehensive climate mitigation strategies.

Enhanced nitrogen removal from secondary effluent of municipal wastewater using denitrification filter: Feasibility of refractory organics as a carbon source

Conventional advanced nitrogen removal in municipal wastewater is hindered by the limited availability of carbon sources in the secondary effluent. However, refractory organics present in it had the potential to serve as intrinsic carbon sources after hydrolysis for nitrogen removal via simultaneous denitrification and partial-denitrification anammox (PDA) processes. To assess this potential, a denitrification filter was set up in this study to evaluate its feasibility of concurrent processes. Results showed that increasing influent ammonium (NH4+-N) from 1.0 to 7.0 mg/L increased total nitrogen (TN) removal from 52.4 % to 89.9 %. Simultaneous occurrence of PDA and denitrification process were confirmed by the actual chemical oxygen demand (COD) consumption (0.8–1.2 mg/mg TN removal) from non-fluorescent organics. The presence of the anammox, hydrolytic and denitrifying bacteria further supported the achievement of nitrogen removal through PDA and denitrification processes by utilizing hydrolytic products biodegraded from refractory organics.

Conserved mechanism of Xrn1 regulation by glycolytic flux and protein aggregation

The regulation of gene expression in eukaryotes relies largely on the action of exoribonucleases, evolutionarily conserved enzymes that digest decapped messenger RNAs in the 5’-3’ direction. The activity of Xrn1, the major yeast exoribonuclease, is regulated by targeted changes in its cellular localisation in direct response to the cell’s metabolic state. When fermentable carbon sources are available, active Xrn1 is diffusely localised in the cytosol. Upon depletion of these sources, Xrn1 is sequestered at the plasma membrane-associated protein complex, the eisosome, and becomes inactive. Although this phenomenon has been described previously, the molecular mechanisms underlying these changes remain unknown. We report that the binding of Xrn1 to the plasma membrane is subject to glycolytic flux, rather than the availability of a fermentable carbon source, is independent of TORC1 activity and requires the core eisosomal proteins Pil1 and Lsp1. We identify the SH3-like domain of the Xrn1 protein as a putative interaction domain. In addition, we show that when expressed in Saccharomyces cerevisiae, the human orthologue of Xrn1 mirrors its yeast counterpart, i.e., it segregates to the eisosome under conditions of halted glycolysis. Our results not only advance our understanding of Xrn1 regulation but also indicate that this regulatory principle is conserved from yeast to humans.

INDUCTION ENDOSPORE FORMATION OF Bacillus subtilis KM16 AS A PROBIOTIC CANDIDATE BY OPTIMIZATION OF THE GROWTH CONDITIONS

Probiotics are living microorganisms which have beneficial effects. One of the benefits is enhancing immunity. Therefore, probiotics are often supplemented into food, medical, and aquaculture products. B. subtilis KM16 as endospore-producing bacteria have been known to increase probiotic resistance to confront the unstable conditions of the digestive tract. Spore formation of Bacillus is supported by the optimal condition of growth medium and incubation periods. The sufficient availability of carbon, nitrogen, and mineral source in the growth medium, and environmental conditions can support the formation of optimal endospores. This research aimed to determine the suitable sugar composition of a medium and optimum incubation time suitable for endospores formation of B. subtilis KM16. Glucose and maltose were utilized as a carbon source in several concentration as a growth medium for B. subtilis KM 16. The incubation time was 48 and 72 hours. The viable number of vegetative cells was not significantly different for the type of sugar and incubation periods. Based on the glucose concentration, 0.2% glucose exhibited the uppermost number of cells, while 1% glucose concentration caused the decrease of vegetative cells. In this study, 0.2% glucose with 48 hours incubation period showed the highest percentage of sporulation frequencies, up to 48%, but it was not significantly different from the other glucose concentration. The medium that contains 0.2% glucose with 48 hours incubation period is the best medium for the utilization of B. subtilis KM16 cells and spores as probiotic candidates.

Synergistic removal of bio-recalcitrant organic compounds and nitrate: Coupling photocatalysis and biodegradation to enhance the bioavailability of electron donors

Nitrate pollution poses significant threats to both aquatic ecosystems and human well-being, particularly due to eutrophication and increased risks of methemoglobinemia. Conventional treatment for nitrate-contaminated wastewater face challenges stemming from limited availability of carbon sources and the adverse impacts of toxins on denitrification processes. This study introduces an innovative Intimately Coupled Photocatalysis and Biodegradation (ICPB) system, which utilizes Ag3PO4/Bi4Ti3O12, denitrifying sludge, and polyurethane sponge within an anoxic environment. This system demonstrates remarkable efficacy in simultaneously removing bio-recalcitrant organic compounds (such as sulfamethoxazole) and nitrates, surpassing standalone treatment methods. Optimally, the ICPB achieves complete removal of sulfamethoxazole, along with 87.7 % removal of DOC, and 81.8 % reduction in nitrate levels. Its ability to sustain pollutant removal and biological activity over multiple cycles can be attributed to the special formation of biofilm and mineralization of sulfamethoxazole, minimizing both photocatalytic damage and toxic inhibitory effects on microbes. The dominant microbial genera of ICPB system included Castellaniella, Acidovorax, Raoultella, Giesbergeria, and Alicycliphilus. Additionally, the study sheds light on a potential mechanism for the concurrent treatment of recalcitrant organics and nitrates by the ICPB system, presenting a novel and highly effective approach for addressing biologically resistant wastewater.

Synergistic mechanisms of denitrification in FeS2-based constructed wetlands: Effects of organic carbon availability under day-night alterations

In constructed wetlands (CWs), carbon source availability profoundly affected microbial metabolic activities engaged in both iron cycle and nitrogen metabolism. However, research gaps existed in understanding the biotransformation of nitrogen and iron in response to fluctuations in organic carbon content under day-night alterations. Results demonstrated increased removal efficiency of NO3−-N (95.7 %) and NH4+-N (75.70 %) under light conditions, attributed to increased total organic carbon (TOC). This enhancement promoted the relative abundance of bacteria involved in nitrogen and iron processes, establishing a more stable microbial network. Elevated TOC content also upregulated genes for iron metabolism and glycolysis, facilitating denitrification. Spearman correlation analysis supported the synergistic mechanisms between FeS2-based autotrophic denitrification and TOC-mediated heterotrophic denitrification under light conditions. The significant impact of carbon sources on microbial activities underscores the critical role of organic carbon availability in enhancing nitrogen removal efficiency, providing valuable insights for optimizing FeS2-based CWs design and operation strategies.

Design and performance of micro-zone C diffusion device to explore the importance of distance for soil microorganisms to utilize available exogenous carbon source

Soil acts as both a major sink and source of carbon in terrestrial ecosystems. Soil microorganisms play an important role in carbon sequestration as well as carbon mobilization. Either substrate to microbe or microbe to substrate transport are important in barren soil environments. Available external carbon sources can be utilized before some soil organic matter components are activated. In this process, external carbon source availability markedly determines soil microorganism activity (e.g., the distance between the carbon source and soil microorganisms). Here, I investigated the role of space as a factor influencing carbon utilization. I designed a soil incubation device that both separated the carbon source from soil microbes and ensured free carbon movement. Dextran was applied to avoid mass flow and maintain a balanced water potential. An isotope-labeling technique was used to quantitatively study carbon diffusion. The microcosm experiment verified that the carbon source was gradually utilized by the soil microorganisms according to the distance gradient. Soil microorganisms close to the carbon source initially used glucose, whereas more remote microbes waited for glucose to be transported. The microbial biomass carbon (MBC) content was much higher at smaller (0–0.5 cm) distances than they did at larger (0.5–1 or 1–2 cm) ones, which indicated that the higher concentration of available carbon source in the space closer to the glucose was conducive to the rapid acquisition and assimilation of microorganisms. The findings of this study establish a methodology and identify potential applications for further analysis of the spatial effects of carbon source availability on soil microbial activity.

The operating temperature affects the efficiency and pathogenic risk of wastewater treatment enhanced by slurry

The insufficient availability of carbon sources in low carbon source wastewater has consistently hampered the nitrogen removal efficiency. This study explored the potential of using anaerobic digested slurry supernatant as an additional carbon source and examined the cost-effective temperature range. The results demonstrated that wastewater treatment within the temperature range of 28 °C to 38 °C could meet the discharge standards set by wastewater treatment plants. However, at 38 °C, the nitrogen-to-carbon consumption ratio decreased to 0.18 g N/g COD. Mechanistic analysis revealed that both excessively high and low temperatures reduced the diversity of microbial communities and influenced the composition of the microbial community through environmental selective pressures. Thauera, Acidovorax, Syntrophomonas, and Acidaminobacter were identified as the dominant genera for nitrogen removal at the temperature of 38 °C, 33 °C, 28 °C, and 23 °C, respectively. Furthermore, high temperature enhanced nitrogen removal performance by promoting microbial activity, microbial transmembrane substance transport process, and the abundance of key genes (HK, pgi1, pfkB, narG, narH, narI) at 38 °C. Importantly, factor score analysis confirmed that the risk of microbial pathogenicity was relatively low at 28 °C. This work provides valuable insights into the optimal temperature parameters and regulatory mechanisms for wastewater treatment systems utilizing slurry as a carbon source. It provides innovative ideas for the clean and safe development of low carbon source wastewater treatment technologies.

Artificial neural network based optimization of sunflower oil supplementation in polyhydroxyalkanoates production by Cupriavidus necator

The assessment of feeding strategy and availability of alternate carbon source in vegetable oil-supplemented microbial polyhydroxyalkanoates (PHA) production remains largely qualitative. This study aims to model the impact of sunflower oil to sucrose ratio, and feeding strategy on PHA production by Cupriavidus necator. Sets containing oil (20 ml l−1), and oil-sucrose mixture (10 ml l−1, 10 g l−1) resulted in 3.907 g l−1 and 3.342 g l−1 of PHA, much higher than in sucrose-only (2.081 g l−1) set. Shifting sucrose (20 g l−1) pre-grown biomass on into oil (20 ml l−1) containing medium resulted in a substantial increase in polymer than in sets either amended with oil or having an equal proportion sucrose-oil blend. Hyperparameter optimized double-layer (6-3) ANN model for PHA production, developed from factorial design experiment with different sucrose-oil ratios (0.053–19 w/v), inoculum dose (0.853–1.219 g l−1), and time-of-shift (24–72 h), offered reasonably good fitness both on training (R2: 0.960) and cross-validation (R2CV: 0.593). Optimization of the ANN model projected 10.411 g l−1 of PHA from a sucrose-oil ratio of 1.729 (w/v), inoculum dose (0.854 g l−1), and sucrose-to-oil shift after 44 h of incubation.

A REVIEW ON THE β-CAROTENE: PRODUCTION, EXTRACTION, SYNTHESIS AND BIOLOGICAL PROPERTIES

The presence of double bonds gives β-carotene its distinctive hue, making it an oxygen-deficient isoprene-containing molecule. There are cyclic rings at both ends of the molecule. The present review was based on the production, extraction, synthesis and biological properties of β-carotene. Mammals can't produce carotenoids from scratch; therefore, they must get them from somewhere else. Algae, higher plants (in fruits and flowers as esters), fungi, and animals all have these yellow, red, and orange pigments in their natural forms. Carotenoids are found in human breast milk and can be modified through the mother's diet. Hexane, tetrahydrofuran, and acetone are examples of aprotic organic solvents that can be used for solvent-based extraction of -carotene from algae after and before they have been treated. The -carotene in algae, fungi, and plants can be extracted with the help of these solvents. The extraction process for -carotene is sped up and improved by the use of supercritical fluids. Increasing beta-carotene production can be accomplished by tailoring a number of environmental factors, including the type of organism used in the cultivation process, the amount of light available, the amount of salt present, the pH level, and the type and availability of carbon sources. Microalgae, plants, and fungus have all been optimised to increase their beta-carotene synthesis. It concluded that when administered in different doses, it has been shown to have effects like antioxidant and anti-inflammatory. it is also effective against cancer, cardiovascular diseases, Covid-19 and various other diseases.

Microbial mechanisms for improved soil phosphorus mobilization in monoculture conifer plantations by mixing with broadleaved trees

Replanting broadleaved trees in monoculture conifer plantations has been shown to improve the ecological environment. However, not much is known about the distribution properties of soil phosphate-mobilizing bacteria (PMB) under different mixed plantings or how PMB affects biometabolism-driven phosphorus (P) bioavailability. The phoD and pqqC genes serve as molecular markers of PMB because they regulate the mobilization of organic (Po) and inorganic (Pi) P. Differences in soil bioavailable P concentration, phoD- and pqqC-harboring PMB communities, and their main regulators were analyzed using biologically-based P (BBP) and high-throughput sequencing approaches after combining coniferous trees (Pinus massoniana) and five individual broadleaved trees (Bretschneidera sinensis, Michelia maudiae, Cercidiphyllum japonicum, Manglietia conifera, and Camellia oleifera). The findings revealed that the contents of litter P, soil organic carbon (SOC), available Pi (CaCl2–P), and labile Po (Enzyme-P) were significantly higher in conifer-broadleaf mixed plantations than those in the monospecific Pinus massoniana plantations (PM), especially in the mixed stands with the introduction of Cercidiphyllum japonicum, Michelia maudiae, and Camellia oleifera. Conifer-broadleaf mixing had little effect on the abundance of phoD and pqqC genes but significantly altered species composition within the communities. Conifer-broadleaf mixing improved soil microbial habitat mainly by increasing the pH, increasing carbon source availability and nutrient content, decreasing exchangeable Fe3+ and Al3+ content, and decreasing the activation degrees of Fe and Al oxides in acidic soils. A small group of taxa (phoD: Bradyrhizobium, Tardiphaga, Nitratireductor, Mesorhizobium, Herbaspirillum, and Ralstonia; pqqC: Burkholderia, Variovorax, Bradyrhizobium, and Leptothrix) played a key role in the synthesis of P-related enzymes (e.g., alkaline phosphomonoesterase, ALP) and in lowering the levels of mineral-occluded (HCl–P) and chelated (Citrate-P) Pi. Overall, our findings highlight that mixing conifers and broadleaves could change the PMB communities that produce ALP and dissolve Pi to make P more bioavailable.

The transcription factor STE12 influences growth on several carbon sources and production of dehydroacetic acid (DHAA) in Trichoderma reesei

The filamentous ascomycete Trichoderma reesei, known for its prolific cellulolytic enzyme production, recently also gained attention for its secondary metabolite synthesis. Both processes are intricately influenced by environmental factors like carbon source availability and light exposure. Here, we explore the role of the transcription factor STE12 in regulating metabolic pathways in T. reesei in terms of gene regulation, carbon source utilization and biosynthesis of secondary metabolites. We show that STE12 is involved in regulating cellulase gene expression and growth on carbon sources associated with iron homeostasis. STE12 impacts gene regulation in a light dependent manner on cellulose with modulation of several CAZyme encoding genes as well as genes involved in secondary metabolism. STE12 selectively influences the biosynthesis of the sorbicillinoid trichodimerol, while not affecting the biosynthesis of bisorbibutenolide, which was recently shown to be regulated by the MAPkinase pathway upstream of STE12 in the signaling cascade. We further report on the biosynthesis of dehydroacetic acid (DHAA) in T. reesei, a compound known for its antimicrobial properties, which is subject to regulation by STE12. We conclude, that STE12 exerts functions beyond development and hence contributes to balance the energy distribution between substrate consumption, reproduction and defense.

Interactions between bacteria and microalgae in microalgal-bacterial symbiotic wastewater treatment systems: mechanisms and influencing factors

Microalgal-bacterial symbiotic wastewater treatment systems (MBSWTSs) have received widespread attention due to their capacity to achieve high pollutant removal efficiency during wastewater treatment, with low energy consumption requirements, efficient carbon sequestration, and wastewater resource utilization. This paper provides an overview of the treatment performance and current research status of MBSWTSs, including a detailed summary of the mechanisms of nitrogen, phosphorus, and carbon removal by MBSWTSs and the interactions between bacteria and microalgae. In particular, this review focuses on the influence of operational parameters on the regulation of the symbiotic system, such as the microalgal:bacterial ratio, N:P ratio, external carbon source, dissolved oxygen concentration, aeration mode, and light availability. Among these factors, the microalgal:bacterial ratio, carbon source, and light availability have an important influence on microalgal-bacterial competition, as well as the trophic mode of the system, biomass production, and the capacity for the process to be practically applied on a large scale. MBSWTSs still have some challenging aspects that have hindered their development and application, such as the unknown mechanism of microalgal-bacterial co-metabolism, limited previous practical applications, algal contamination, and harvesting difficulties. To overcome these challenges, future research requires a multidisciplinary approach, incorporating life sciences, material science, and other disciplines. Comprehensive research should be conducted on the metabolic mechanisms of MBSWTSs, the optimization of process performance and waste resource utilization, providing a theoretical and practical foundation for the practical application of MBSWTSs.

Implications in the production of defossilized methanol: A study on carbon sources

The transition of the current fossil based chemical industry to a carbon-neutral industry can be done by the substitution of fossil carbon for defossilized carbon in the production of base chemicals. Methanol is one of the seven base chemicals, which could be used to produce other base chemicals (light olefins and aromatics). In this research, we evaluated the synthesis of methanol based on defossilized carbon sources (maize, waste biomass, direct air capture of CO2 (DAC), and CO2 from the cement industry) by considering carbon source availability, energy, water, and land demand. This evaluation was based on a carbon balance for each of the carbon sources. Our results show that maize, waste biomass, and CO2 cement could supply 0.7, 2, 15 times the carbon demand for methanol respectively. Regarding the energy demand maize, waste biomass, DAC, and CO2 from cement demand 25, 21, 48, and 45GJtonMeOH separately. The demand for water is 5300, 220, 8, and 8m3tonMeOH. And lastly, land demand was estimated to 1031, 36, 83, and 77m2tonMeOH per carbon source. The high-demanding-resource production of defossilized methanol is dependent on the availability of resources per location. Therefore, we analyzed the production of defossilized methanol in the Netherlands, Saudi Arabia, China, and the USA. China is the only country where CO2 from the cement industry could provide all the demand of carbon. But as we envision society becoming carbon neutral, CO2 from the cement industry would diminish in time, as a consequence, it would not be sufficient to supply the demand for carbon. DAC would be the only source able to provide the demand for defossilized carbon.

Mycobacterium tuberculosis response to cholesterol is integrated with environmental pH and potassium levels via a lipid metabolism regulator.

Successful colonization of the host requires Mycobacterium tuberculosis (Mtb) to sense and respond coordinately to disparate environmental cues during infection and adapt its physiology. However, how Mtb response to environmental cues and the availability of key carbon sources may be integrated is poorly understood. Here, by exploiting a reporter-based genetic screen, we have unexpectedly found that overexpression of transcription factors involved in Mtb lipid metabolism altered the dampening effect of low environmental potassium concentrations ([K+]) on the pH response of Mtb. Cholesterol is a major carbon source for Mtb during infection, and transcriptional analyses revealed that Mtb response to acidic pH was augmented in the presence of cholesterol and vice versa. Strikingly, deletion of the putative lipid regulator mce3R had little effect on Mtb transcriptional response to acidic pH or cholesterol individually, but resulted specifically in loss of cholesterol response augmentation in the simultaneous presence of acidic pH. Similarly, while mce3R deletion had little effect on Mtb response to low environmental [K+] alone, augmentation of the low [K+] response by the simultaneous presence of cholesterol was lost in the mutant. Finally, a mce3R deletion mutant was attenuated for growth in foamy macrophages and for colonization in a murine infection model that recapitulates caseous necrotic lesions and the presence of foamy macrophages. These findings reveal the critical coordination between Mtb response to environmental cues and cholesterol, a vital carbon source, and establishes Mce3R as a transcription factor that crucially serves to integrate these signals.

Regulation of Aerobic Succinate Transporter dctA of E. coli by cAMP-CRP, DcuS-DcuR, and EIIAGlc: Succinate as a Carbon Substrate and Signaling Molecule

Introduction: C4-dicarboxylates (C4-DC) have emerged as significant growth substrates and signaling molecules for various Enterobacteriaceae during their colonization of mammalian hosts. Particularly noteworthy is the essential role of fumarate respiration during colonization of pathogenic bacteria. To investigate the regulation of aerobic C4-DC metabolism, the study explored the transcriptional control of the main aerobic C4-DC transporter, dctA, under different carbohydrate conditions. In addition, mutants related to carbon catabolite repression (CCR) and C4-DC regulation (DcuS-DcuR) were examined to better understand the regulatory integration of aerobic C4-DC metabolism into CCR. For initial insight into posttranslational regulation, the interaction between the aerobic C4-DC transporter DctA and EIIAGlc from the glucose-specific phosphotransferase system was investigated. Methods: The expression of dctA was characterized in the presence of various carbohydrates and regulatory mutants affecting CCR. This was accomplished by fusing the dctA promoter (PdctA) to the lacZ reporter gene. Additionally, the interaction between DctA and EIIAGlc of the glucose-specific phosphotransferase system was examined in vivo using a bacterial two-hybrid system. Results: The dctA promoter region contains a class I cAMP-CRP-binding site at position −81.5 and a DcuR-binding site at position −105.5. DcuR, the response regulator of the C4-DC-activated DcuS-DcuR two-component system, and cAMP-CRP stimulate dctA expression. The expression of dctA is subject to the influence of various carbohydrates via cAMP-CRP, which differently modulate cAMP levels. Here we show that EIIAGlc of the glucose-specific phosphotransferase system strongly interacts with DctA, potentially resulting in the exclusion of C4-DCs when preferred carbon substrates, such as sugars, are present. In contrast to the classical inducer exclusion known for lactose permease LacY, inhibition of C4-DC uptake into the cytoplasm affects only its role as a substrate, but not as an inducer since DcuS detects C4-DCs in the periplasmic space (“substrate exclusion”). The work shows an interplay between cAMP-CRP and the DcuS-DcuR regulatory system for the regulation of dctA at both transcriptional and posttranslational levels. Conclusion: The study highlights a hierarchical interplay between global (cAMP-CRP) and specific (DcuS-DcuR) regulation of dctA at the transcriptional and posttranslational levels. The integration of global and specific transcriptional regulation of dctA, along with the influence of EIIAGlc on DctA, fine-tunes C4-DC catabolism in response to the availability of other preferred carbon sources. It attributes DctA a central role in the control of aerobic C4-DC catabolism and suggests a new role to EIIAGlc on transporters (control of substrate uptake by substrate exclusion).

Effects of Cellulosic Carbon Addition on Nitrogen Removal from Simulated Dry Land Drainage, and Its Environmental Effects

Agricultural non-point source pollution has emerged as a significant driver of declining global water quality in recent years. Ditch systems hold considerable promise for trapping and purifying pollutants. However, the persistent challenge has been the limited availability of carbon sources in drainage water, which significantly hinders nitrogen (N) removal in ditches. This study investigated the dynamic changes in ammonia (NH4+) and nitrate (NO3−) levels caused by three cellulosic carbon additions (rice straw, coir, and sawdust) during both winter and summer seasons. Water column devices were used as containers, and the impacts on environmental factors and water denitrification rates were explored. Results demonstrated that the addition of straw exhibited the most effective N removal in winter and summer, and significantly enhanced water denitrification rates in a short timeframe, with the maximum denitrification rate reaching 1482.42 μmol·L−1·h−1. However, there was an observed accumulation of NH4-N and chemical oxygen demand (COD) in summer. Also, the addition of sawdust resulted in a notable increase in greenhouse gas emissions during the summer test. In conclusion, during the cooler seasons of winter and spring when temperatures are not as high, the combined use of various cellulosic carbon sources has the potential to enhance water denitrification and mitigate adverse environmental impacts, offering valuable applications for water quality improvement.

N2O emission reduction in the biological nitrogen removal process for wastewater with low C/N ratios: mechanisms and strategies

Urban wastewater, as the main influent type of Waste Water Treatment Plants (WWTPs), has the characteristic of low carbon to nitrogen ratio (C/N). In the biological nitrogen removal (BNR) process, insufficient carbon source often affects the nitrogen removal efficiency and leads to more N2O emissions. We review recent researches on N2O emissions in the BNR process of wastewater with low C/N. The availability of carbon sources affects heterotrophic denitrification (HD) and autotrophic nitrification/denitrification processes, which are the main reasons for N2O emissions in BNR. For the sustainable development of BNR in WWTPs, we introduce strategies suitable for reducing N2O emissions in the BNR process of low C/N wastewater from two aspects: traditional process innovation and new process development. These strategies mainly include carbon source addition, adjustment of aeration strategy, optimization of oxidation ditch and biofilm facilities, and application of Anammox related processes. In the future, it is still necessary to further deepen this research direction through the normalization of N2O emission quantification standards, exploration of N2O metabolism mechanisms, assessment of environmental effects of emission reduction strategies, and practical application of new processes.

Microbial nitrogen mineralization is slightly affected by conversion from farmland to apple orchards in thick loess deposits

Organic nitrogen mineralization, indispensable to soil carbon and nitrogen cycles, is the largest contributor to nitrate reservoirs in deep vadose zones. The microbial nitrogen mineralization (MNM) within deep soils, particularly in regions with intensive agricultural activities and thick soil horizons, has been largely disregarded. As such, this study aims to address this knowledge gap by investigating the chiA-harboring microbial structure and network within nine 10-m profiles beneath cultivated farmland and two apple orchards. The results showed that apple orchards, compared to farmland, had considerable water deficit and nitrogen accumulation within deeper soil layers due to well-developed root systems and the overuse of chemical fertilizers. However, the chiA-harboring microbial diversity, composition, and abundance all exhibited significant variations with soil depths rather than being influenced by different land use types. Moreover, the diversity indices and gene abundances decreased with soil depths, and the related soil microbes included 19 phyla, 29 classes, 72 orders, 114 families, and 197 genera, with Actinobacteria and Proteobacteria being the two major bacterial phyla. The microbial co-occurrence network was simper beneath apple orchards. The chiA-harboring microorganisms within deep unsaturated zones were greatly influenced by the depth-dependent soil nutrients, such as total nitrogen, organic carbon, and available potassium. The limited plant root biomass and the inhibitory effects of dried soil layers both restricted the availability of carbon sources, which further interfered with the MNM processes within deep soils insignificantly. Therefore, despite the considerable plant-induced ecohydrological consequences, the depth-dependent MNM processes were slightly affected after the transformation from farmland to apple orchards within thick loess deposits. This study offers crucial insights into microbial dynamics of the deep biosphere, thereby contributing to our understanding of depth-dependent biogeochemical cycles within global deep unsaturated zones.