Decadal shifts in Qingzang Plateau lake carbon dynamics (1970-2020): From predominant carbon sources to emerging sinks

The evasion of carbon dioxide (CO2) from lakes significantly influences the global carbon equilibrium. Amidst global climatic transformations, the role of Qingzang Plateau (QZP) lakes as carbon (C) sources or sinks remains a subject of debate. Furthermore, accurately quantifying their contribution to the global carbon budget presents a formidable challenge. Here, spanning half a century (1970-2020), we utilize a synthesis of literature and empirical field data to assess the CO2 exchange flux of QZP lakes. We find markedly higher CO2 exchange flux in the southeast lakes than that in the northern and western regions from 1970 to 2000. During this time, both freshwater and saltwater lakes served primarily as carbon sources. The annual CO2 exchange flux was estimated at 2.04 ± 0.37 Tg (Tg) C yr-1, mainly influenced by temperature fluctuations. The CO2 exchange flux patterns underwent a geographical inversion between 2000 and 2020, with increased levels in the west and decreased levels in the east. Notably, CO2 emissions from freshwater lakes diminished, and certain saltwater lakes in the QTP transitioned from carbon sources to sinks. From 2000 to 2020, the annual CO2 exchange flux from QZP lakes is estimated at 1.34 ± 0.50 Tg C yr-1, with solar radiation playing a more pronounced role in carbon emissions. Cumulatively, over the past five decades, QZP lakes have generally functioned as carbon sources. Nevertheless, the total annual CO2 emissions have declined since the year 2000, indicating a potential shift trend from being a carbon source to a sink, mirroring broader patterns of global climate change. These findings not only augment our understanding of the carbon cycle in plateau aquatic systems but also provide crucial data for refining China's carbon budget.

Can xenobiotics support the growth of Mn(II)-oxidizing bacteria (MnOB)? A case of phenol-utilizing bacteria Pseudomonas sp. AN-1

Biogenic manganese oxides (BioMnOx) produced by Mn(II)-oxidizing bacteria (MnOB) have garnered considerable attention for their exceptional adsorption and oxidation capabilities. However, previous studies have predominantly focused on the role of BioMnOx, neglecting substantial investigation into MnOB themselves. Meanwhile, whether the xenobiotics could support the growth of MnOB as the sole carbon source remains uncertain. In this study, we isolated a strain termed Pseudomonas sp. AN-1, capable of utilizing phenol as the sole carbon source. The degradation of phenol took precedence over the accumulation of BioMnOx. In the presence of 100 mg L-1 phenol and 100 µM Mn(II), phenol was entirely degraded within 20 h, while Mn(II) was completely oxidized within 30 h. However, at the higher phenol concentration (500 mg L-1), phenol degradation reduced to 32% and Mn(II) oxidation did not appear to occur. TOC determination confirmed the ability of strain AN-1 to mineralize phenol. Based on the genomic and proteomics studies, the Mn(II) oxidation and phenol mineralization mechanism of strain AN-1 was further confirmed. Proteome analysis revealed down-regulation of proteins associated with Mn(II) oxidation, including MnxG and McoA, with increasing phenol concentration. Notably, this study observed for the first time that the expression of Mn(II) oxidation proteins is modulated by the concentration of carbon sources. This work provides new insight into the interaction between xenobiotics and MnOB, thus revealing the complexity of biogeochemical cycles of Mn and C.

Environmental impacts on algal-bacterial-based aquaponics system by different types of carbon source addition: water quality and greenhouse gas emission

Carbon source addition is an important way improving the carbon and nitrogen transformation in aquaculture system; however, its effectiveness of algal-bacterial-based aquaponics (AA) through carbon source addition is still vague. In this study, the influences of organic carbon (OC-AA system) and inorganic carbon (IC-AA system) addition and without carbon source addition (C-AA system) on the operational performance of AA system were investigated. Results showed that 10.1-19.5% increase of algal-bacterial biomass enhanced the purifying effect of ammonia nitrogen in OC-AA system and IC-AA system relative to C-AA system. Moreover, extra electron donor supply in the OC-AA system obtained the lowest NO3--N concentration. However, that was at the cost of aggravated N2O conversion ratio, which increased by more than 2.0-folds than other systems, attributing to 2.9-folds increase of nirS gene abundance. In addition, carbon source addition increased the pH and then decreased the fish biomass production of AA system. The results of this study would provide theoretical supports of carbon source addition on the performance of nutrient transformation and greenhouse gas effect in AA system.

Heavy metal tolerance, and metal biosorption by exopolysaccharides produced by bacterial strains isolated from marine hydrothermal vents

The present study highlights heavy metal tolerance, EPS production, and biosorption capacity of four hydrothermal vent bacterial strains, namely Exiguobacterium aquaticum, Mammaliicoccus sciuri, Micrococcus luteus, and Jeotgalicoccus huakuii against As, Cd, Cr, Cu, Co, Pb and Ni. The biosorption assay showed high removal efficiency of As (83%) by E. aquaticum, Cd (95%) by M. sciuri, Cu (94%) by M. luteus, and Ni (89%) by J. huakuii and their produced EPS with these metals in aqueous solution were 84%, 85%, 98%, and 91%, respectively. The maximum EPS yield was attained by optimized medium composition consisting of 1% Xylose, and 1% NaCl at pH 7. In metal-amended conditions, the four bacterial strains showed induced EPS production in the initial concentrations. SEM with EDX and CLSM images showed that the growth and EPS production of bacterial strains were affected by metal ion concentrations. A phenol sulphuric acid method and BCA assay were used to identify both the carbohydrate and total protein content of four extracted EPS. A DPPH assay revealed that EPS influences free radical scavenging and has a highly enhanced synergistic effect with its antioxidant activity. FT-IR analysis of four extracted EPS showed the shifting of peaks in the functional groups of EPS before and after adsorption of metal ions. At pH 5 and after 60 min contact time metal removal efficiency and adsorption capacity increased as calculated for As, Cd, Cu, and Ni by four extracted EPS: (86%, 20 mg/g), (74%, 19 mg/g), (94%, 60 mg/g) and (89%, 32 mg/g) and (89%, 16 mg/g), (85%, 16 mg/g), (96%, 22 mg/g) and (91%, 16 mg/g), respectively. The Langmuir compared to the Freundlich model was found to better represent the adsorption by EPS providing maximum adsorption capacities for As (34.65 mg/g), Cd (52.88 mg/g), Cu (24.91 mg/g), and Ni (58.38 mg/g).

Chemical characteristics of dissolved organic matter in effluent from sludge alkaline fermentation liquid-fed sequencing batch reactors

Sludge alkaline fermentation liquid (SAFL) is a promising alternative to acetate for improving biological nitrogen removal (BNR) from wastewater. SAFL inevitably contains some refractory compounds, while the characteristics of dissolved organic matter (DOM) in effluent from SAFL-fed BNR process remain unclear. In this study, the molecular weight distribution, fluorescent composition and molecular profiles of DOM in effluent from SAFL and acetate-fed sequencing batch reactors (S-SBRs and A-SBRs, respectively) at different hydraulic retention time (12 h and 24 h) was comparatively investigated. Two carbon sources resulted in similar effluent TN, but a larger amount of DOM, which was bio-refractory or microorganisms-derived, was found in effluent of S-SBRs. Compared to acetate, SAFL increased the proportion of large molecular weight organics and humic-like substances in effluent DOM by 74.87%-101.3% and 37.52%-48.35%, respectively, suggesting their bio-refractory nature. Molecular profiles analysis revealed that effluent DOM of S-SBRs exhibited a more diverse composition and a higher proportion of lignin-like molecules. Microorganisms-derived molecules were found to be the dominant fraction (71.51%-72.70%) in effluent DOM (<800 Da) of S-SBRs. Additionally, a prolonged hydraulic retention time enriched Bacteroidota, Haliangium and unclassified_f_Comamonadaceae, which benefited the degradation of DOM in S-SBRs. The results help to develop strategies on reducing effluent DOM in SAFL-fed BNR process.

Impacts of seasonal variation on volatile fatty acids production of food waste anaerobic fermentation

This study aims to investigate the influence of seasonal variations on Volatile fatty acids (VFAs) production from food waste (FW) and to quantify their impact. Results of batch experiments with external pH control indicated that the properties of FW exhibited significant seasonal variations and were markedly different from kitchen waste (KW). The spring group demonstrated the highest VFA concentration and VFA/SCOD, at 31.24 g COD/L and 92.20 % respectively, which were 1.22 and 1.27 times higher than those observed in the summer season. The combined proportion of acetic acid and butyric acid accounted for 81.10 % of the total VFAs in spring, suggesting the highest applicability to the carbon source. The VFA content of all seasonal groups in descending order was butyric acid, propionic acid and acetic acid. Carbohydrates, along with spicy and citrusy substances, promoted the conversion of total VFA and butyric acid, while proteins and lipids favored the production of acetic acid and propionic acid.

Applying sludge hydrolysate as a carbon source for biological denitrification after composition optimization via red soil filtration

Sludge hydrolysate, the byproduct generated during sludge hydrothermal treatment (HT), is a potential carbon source for biological denitrification. However, the refractory organic matters and the nutrient substances are unfavorable to the nitrogen removal. In this study, effects of HT conditions on the hydrolysate properties, and the hydrolysate compositions optimization via red soil (RS) filtration were investigated. At HT temperature of 160-220 °C and reaction time of 1-4 h, the highest dissolution rate of organics from sludge to hydrolysate achieved 70.1 %, while the acetic acid dominated volatile fatty acids (VFAs) was no more than 5.0 % of the total organic matter content. The NH4+-N and dissolved organic nitrogen (DON) were the main nitrogen species in hydrolysate. When the hydrolysate was filtered by RS, the high molecular weight organic matters, DON, NH4+ and PO43- were effectively retained by RS, while VFAs and polysaccharide favorable for denitrification were kept in the filtrate. When providing same COD as the carbon source, the filtrate group (Fi-Group) introduced lower concentrations of TN and humic substances but higher content of VFAs. This resulted in TN removal rate (57.0 %) and denitrification efficiency (93.6 %) in Fi-Group higher than those in hydrolysate group (Hy-Group), 39.4 % and 83.7 %, respectively. It is noticeable that both Hy- and Fi- Groups up-regulated most of denitrification functional genes, and increased the richness and diversity of denitrifying bacteria. Also, more denitrifying bacteria genera appeared, and their relative abundance increased significantly from 3.31 % in Control to 21.15 % in Hy- Group and 31.31 % in Fi-Group. This indicates that the filtrate is a more suitable carbon source for denitrification than hydrolysate. Moreover, the pH rose from 4.6 ± 0.14 to 6.5 ± 0.05, and the organic carbon, TN, TP and cation exchange capacity (CEC) of RS increased as well after being filtered, implying that the trapped compounds may have the potential to improve soil quality. This study provides a new insight for hydrolysate application according to its composition characteristics, and helps make the most use of wasted sludge.

Eutrophication and loss of riparian shading influence food quality and trophic relation in stream food webs

Eutrophication induced by excessive inputs of nutrient is one of the main stressors in aquatic ecosystems. Deforestation in riparian zones alter riparian shading, which together with eutrophication is expected to exert a complex control over stream food webs. We manipulated two levels of riparian shading (open canopy vs. shading canopy) and nutrient supply (ambient vs. nutrient addition) in three headwater streams to investigate the individual and combined effects of eutrophication and loss of riparian shading on carbon sources and nutritional quality of biofilms, and the subsequent trophic effects on macroinvertebrate grazers. Nutrient enrichment increased the autochthonous carbon (i.e., algae especially diatoms) indicated by fatty acid (FA) biomarkers within biofilms and grazers. The nutritional quality indicated by eicosapentaenoic acid (EPA) content of biofilms was increased with nutrient enrichment and more so with the combined effect of an increase in riparian shading, consequently leading to an increase in the nutritional quality, density, and biomass of grazers. In particular, the trophic linkages between biofilms and grazers were mainly influenced by EPA concentration in the biofilms, and strengthened with the combined effects of riparian shading and additional nutrients. Our study emphasizes the nutritional significance of EPA for consumers at higher trophic levels and proposes its potential as an indicator for monitoring the health of aquatic ecosystems.

Enhanced denitrification of biodegradable polymers using Bacillus pumilus in aerobic denitrification bioreactors: Performance and mechanism

Nitrate accumulation is an important issue that affects animal health and causes eutrophication. This study combined biodegradable polymers with degrading bacteria to lead to high denitrification efficiency. The results showed polycaprolactone had the highest degradation and carbon release rate (0.214 mg/g∙d) and nitrogen removal was greatest when the Bacillus pumilus and Halomonas venusta ratio was 1:2. When the hydraulic retention time was extended to 12 h, the nitrate removal rate for H. venusta with B. pumilus and polycaprolactone increased by 48 %. Furthermore, the group with B. pumilus contained more Proteobacteria (77.34 %) and denitrifying functional enzymes than the group without B. pumilus. These findings indicated B.pumilus can enhance the degradation of biodegradable polymers especially polycaprolactone to improve the denitrification of the aerobic denitrification bacteria H.venusta when treating maricultural wastewater.

Carbon dioxide and methane as carbon source for the production of polyhydroxyalkanoates and concomitant carbon fixation

The currently used plastics are non-biodegradable, and cause greenhouse gases (GHGs) emission as they are petroleum-based. Polyhydroxyalkanoates (PHAs) are biopolymers with excellent biodegradability and biocompatibility, which can be used to replace petroleum-based plastics. A variety of microorganisms have been found to synthesize PHAs by using typical GHGs: carbon dioxide and methane as carbon sources. Converting carbon dioxide (CO2) and methane (CH4) to PHAs is an attractive option for carbon capture and biodegradable plastic production. In this review, the microorganisms capable of using CO2 and CH4 to produce PHAs were summarized. The metabolic mechanism, PHAs production process, and the factors influencing the production process are illustrated. The currently used optimization techniques to improve the yield of PHAs are discussed. The challenges and future prospects for developing economically viable PHAs production using GHGs as carbon source are identified. This work provides an insight for achieving carbon sequestration and bioplastics based circular economy.

Performance and mechanism of chromium reduction in denitrification biofilm system with different carbon sources

In the process of biological reduction of Cr(VI), the type of carbon sources affects the rate and effect of Cr(VI) reduction, but its specific performance and influencing mechanism have not yet been explored. In this study, four denitrification biofilm reactors were operated under four common carbon sources (C6H12O6, CH3COONa, CH3OH, CH3COONa:C6H12O6 1:1) to reveal the impact of carbon sources on Cr(VI) reduction. Through preliminary experimental concentration research, 75 mg/L Cr(VI) was selected as the dosing concentration. In long-term operation, the composite carbon sources of CH3COONa and C6H12O6 demonstrated excellent stability and achieved an impressive Cr(VI) removal efficiency of 99.5 %. The following sequence was C6H12O6, CH3COONa, and CH3OH. Among them, CH3OH was less competitive and the system was severely unbalanced with lowest Cr(VI) reduction efficiency. The toxicity reactions, changes in EPS and its functional groups, and electron transfer revealed the reduction and fixation mechanism of chromium on denitrification biofilm. The changes in microbial communities indicated that microbial communities in composite carbon sources can quickly adapt to the high toxic environment. The proportion of Trichococcus reached 43.6 %, which played an important role in denitrification and Cr(VI) reduction. Meanwhile, the prediction of microbial COG function reflected its excellent metabolic ability and defense mechanism.

Isolation of a marine-derived yeast with potential applications in industrial nitrite utilizing

The nitrite efficient utilization microorganism Wickerhamomyces anomalus RZWP01 was identified. Using nitrite and ammonium as the sole nitrogen source, the nitrogen removal rate of W. anomalus RZWP01 was 97.4% and 87.1%, respectively. W. anomalus RZWP01 grew well in the nitrite medium with glucose or xylose as the only carbon source. However, the W. anomalus RZWP01 cannot live on the nitrite medium with lactose, citric acid, and methanol as the only carbon source. The maximal cell concentration occurred in the nitrite medium with glucose as the only carbon source at a C/N ratio of 20 for 48 h, reaching 8.92 × 108 cell mL-1. W. anomalus RZWP01 was the first reported yeast that can efficiently utilize nitrite. The isolation and identification of W. anomalus RZWP01 enriched the microbial resources of nitrite-degrading microorganisms and provided functional microorganisms for the water treatment of sustainable aquaculture.

Influence of ammonia nitrogen management strategies on microbial communities in biofloc-based aquaculture systems

Controlling ammonia nitrogen is very important in intensive aquaculture. This study evaluated how different management strategies, i.e., chemoautotrophic (control), heterotrophic bacterial enhancement using carbon in glucose or polyhydroxy butyrate-hydroxy valerate (PHBV), and mature biofloc application, affect water quality and microbial community structure and composition. The management strategies were examined during the domestication and fish culture stages. In the domestication stage, the average NO2--N concentration, pH, and DO in the glucose-added groups were significantly lower than those in the control and PHBV groups. All water quality parameters differed significantly among treatment groups in the culture stage. Carbon additions decreased both bacterial richness and diversity in the fish culture stage. Both principal coordinate analysis and hierarchical cluster analysis grouped the 33 bacteria community samples from the two stages into four clusters, which were closely related to management strategy. The dominant taxa of the clusters were identified using linear discriminant analysis effect size (LEfSe). The biomarkers of Cluster I included Marinomonas, Photobacterium, and Vibrio. Porticoccus and Clade-1a were identified as the biomarkers of Cluster II. Marivia, Leucothrix, and Phaeodactylibacter were identified as the biomarkers of Cluster IV. The Cluster I biomarkers were positively correlated with NO2--N, while those of Cluster IV were positively correlated with NO3--N. The redundancy analysis showed that the bacterial communities and biomarkers were influenced by water quality parameters. Quantitative real-time PCR analysis revealed significant differences in the abundances of the amoA and nxrB genes among treatments and between the two stages. The abundance of the amoA gene was higher in the control group than in the carton-added treatments at the ends of both stages. This study provides an important theoretical basis for the selection of efficient ammonia nitrogen control strategies in aquaculture systems.

Chemical weathering in glacial catchment acting as a net carbon source

Over geological time scales, continental silicate weathering is considered as a critical carbon sink that regulates long-term climate feedback. By contrast, recent studies indicate that sulfide oxidation during weathering can be as a potential carbon source. However, whether chemical weathering in glacial conditions characterized by extreme erosion is a net carbon sink or source remains elusive. Here, we present the seasonal carbon cycle processes in a typical glacier catchment, via high-resolution (weekly) river water sampling during the whole 2017 in the Laohugou river, northeastern Tibetan Plateau. Our seasonal result shows that the release of CO2 by sulfide oxidation during the monsoon period can be much faster than CO2 consumption through weathering of silicate rocks, with maximum of ∼26 times. Extending to global glacial basins, we observed a consistent pattern that inorganic carbon releases in alpine glaciers are faster than atmospheric CO2 consumption. We propose that weathering in global glacial environment acts as a significant carbon source, and thus affects climate feedback.

Application of alkali-heated corncobs enhanced nitrogen removal and microbial diversity in constructed wetlands for treating low C/N ratio wastewater

Lack of carbon source is the main limiting factor in the denitrification of low C/N ratio wastewater in the constructed wetlands (CWs). Agricultural waste has been considered as a supplementary carbon source but research is still limited. To solve this problem, ferric carbon (Fe-C) + zeolite, Fe-C + gravel, and gravel were used as substrates to build CWs in this experiment, aiming to investigate the effects of different carbon sources (rice straw, corncobs, alkali-heated corncobs) on nitrogen removal performance and microbial community structure in CWs for low C/N wastewater. The results demonstrated that the microbial community and effluent nitrogen concentration of CWs were mainly influenced by the carbon source rather than the substrate. Alkali-heated corncobs significantly enhanced the removal of NO2--N, NH4+-N, NO3-N, and TN. Carbon sources addition increased microbial diversity. Alkali-heated corncobs addition significantly increased the abundance of heterotrophic denitrifying bacteria (Proteobacteria and Bacteroidota). Furthermore, alkali-heated corncobs addition increased the copy number of nirS, nosZ, and nirK genes while greenhouse gas fluxes were lower than common corncobs. In summary, alkali-heated corncobs can be considered as an effective carbon source.

Short-chain fatty acids facilitated long-term dechlorination of PCBs in Taihu Lake sediment microcosms: Evidence from PCB congener and microbial community analyses

Microbial reductive dechlorination hosts great promise as an in situ bioremediation strategy for polychlorinated biphenyls (PCBs) contamination. However, the slow dechlorination in sediments limits natural attenuation. Short-chain fatty acids, as preferred carbon sources and electron donors for dechlorinating microorganisms, might stimulate PCB dechlorination. Herein, two sets of short-chain fatty acids, sole acetate and a fatty acid mixture (acetate, propionate, and butyrate), were amended periodically into Taihu Lake (China) sediment microcosms containing nine PCB congeners (PCB5, 12, 64, 71, 105, 114, 149, 153, and 170) after 24 weeks of incubation. Short-chain fatty acids facilitated the long-term PCB dechlorination and the promoting effect of the fatty acid mixture compared favorably with that of sole acetate. By the end of 108 weeks, the total PCB mass concentrations in acetate amended and fatty acid mixture amended microcosms significantly declined by 7.6% and 10.3% compared with non-amended microcosms (P < 0.05), respectively. Short-chain fatty acids selectively favored the removal of flanked meta and single-flanked para chlorines. Notably, a rare ortho dechlorination pathway, PCB25 (24-3-CB) to PCB13 (3-4-CB), was enhanced. Supplementary fatty acids significantly increased reductive dehalogenases (RDase) gene pcbA5 instead of improving the growth of Dehalococcoides. These findings highlight the merits of low cost short-chain fatty acids on in situ biostimulation in treating PCBs contamination.

Exploring influence mechanism of small-molecule carbon source on heterotrophic nitrification-aerobic denitrification process from carbon metabolism, nitrogen metabolism and electron transport process

The heterotrophic nitrification-aerobic denitrification (HNAD) process can remove nitrogen and organic carbon under aerobic conditions. To get the in-depth mechanism of the HAND process, a strain named Acinetobacter johnsonii ZHL01 was isolated, and enzyme activity, electron transport, energy production, and gene expression of the strain were studied with small-molecule carbon sources, including sodium citrate, sodium acetate, sodium fumarate, and sodium succinate. The HNAD pathway of ZHL01 was NH4+→NH2OH → NO, and nitrogen balance analysis shows that ZHL01 could assimilate and denitrify 58.29 ± 1.05 % and 16.58 ± 1.07 % of nitrogen, respectively. The assimilation, the nitrification/denitrification, and the respiration processes were regulated by the concentration of reduced nicotinamide adenine dinucleotide (NADH) produced from the different metabolic pathways of small-molecule carbon sources. The HNAD process occurs to reduce intracellular redox levels related to NADH concentrations. This discovery provides a theoretical basis for the practical application of HAND bacteria.

Pineapple core from the canning industrial waste for bacterial cellulose production by Komagataeibacter xylinus

To address the high production cost associated with bacterial cellulose (BC) production using the Hestrin-Schramm (HS) medium, alternative agricultural wastes have been investigated as potential low-cost resources. This study aims to utilize pineapple core from pineapple canning industry waste as a carbon source to enhance the bacterial growth of Komagataeibacter xylinus and to characterize the physical and mechanical properties of the resulting BC. To assess growth performance, commercial sugar at concentrations of 0, 2.5, and 5.0 % (w/v) was incorporated into the medium. Fermentation was conducted under static conditions at room temperature for 5, 10, and 15 days. The structural and physical properties of BC were characterized using SEM, FTIR, XRD, and DSC. With the exception of crystallinity, BC produced from the pineapple core medium exhibited comparable characteristics to BC produced in the HS medium. These findings highlight the potential of utilizing pineapple core, a byproduct of the canning industry, as an economically viable nutrient source for BC production.

Response of nitrite accumulation, sludge characteristic and microbial transition to carbon source during the partial denitrification (PD) process

Partial denitrification (PD, nitrate (NO3--N) → nitrite (NO2--N)) as a novel pathway for NO2--N production has been widely concerned, but the specific conditions for highly efficient and stable nitrite maintenance are not yet fully understood. In this study, the effects of carbon sources (acetate, R1; propionate, R2; glucose, R3) on NO2--N accumulation was discussed without seeding PD sludge and the mechanism analysis related to sludge characteristic and microbial evolution were elucidated. The optimal NO2--N, nitrate-to-nitrite transformation ratio (NTR) and nitrite removal efficiency (NRE) reached up to 32.10 mg/L, 98.01 %, and 86.95 % in R1. However, due to the complex metabolic pathway of glucose, the peak time of NO2--N production delayed from 30 min to 60 min. The sludge particle size decreased from 154.2 μm (R1), 130.8 μm (R2) to 112.6 μm (R3) with the increasing extracellular polymeric substances (EPS) from 80.75-85.44 mg/gVSS, 82.68-92.75 mg/gVSS to 106.31-110.25 mg/gVSS, where the ratio of proteins/polysaccharides (PN/PS) was proved to be closely associated with NO2--N generation. For the microbial evolution, Saccharimonadales (70.42 %) dominated the glucose system, while Bacillus (7.42-21.63 %) and Terrimonas (4.24-5.71 %) were the main contributors for NO2--N accumulation in the acetate and propionate systems. The achievement of PD showed many advantages of lower carbon demand, minimal sludge production, lesser greenhouse gas emission and prominent nutrient removal, offering an economically and technically attractive alternative for NO3--N containing wastewater treatment.

under carbon source-induced reinforcement

This paper describes a unique molecular mechanism for the EPS-mediated synthesis of CdS QDs by sulfate-reducing bacteria (SRB) under carbon source-induced reinforcement. Under the induced by carbon sources (HCOONa, CH3COONa and C6H12O6), there was a significant increase in EPS production of SRB, particularly in protein, and the capacity of Cd(II) adsorption was further enhanced. CdS QDs were extracellularly synthesized by adding S2- after Cd(II) adsorption. The results showed that CdS QDs were wrapped or adhered by EPS, and the most significant increase in Arg and Lys among basic amino acids in EPS after HCOONa-induced was 133.34% and 63.89%, respectively. This may serve as a biological template for QD synthesis, producing protein gels with a large number of microcavities and controlling the nucleation of CdS QDs. The highest yield of HCOONa-CdS was achieved after induction, with 23.59 g/g biomass per unit strain, which was 447.34% higher than that before induction and was at a high level in previous studies. The synthesized CdS QDs were uniform in size distribution and had higher luminescence activity and a larger specific surface area than those synthesized by the chemical synthesis route, provides a new idea for EPS treatment of heavy metal wastewater and metal biorecovery.

Analysis of energy-related CO2 emissions in Pakistan: carbon source and carbon damage decomposition analysis

Carbon dioxide emissions (CO2es) are presently a hot topic of worldwide concern. It is of great significance for lessening CO2es to wholly understand the transformation pattern of CO2es among countries, industries, and the main factors (i.e., emission effect, energy intensity, economic development, population size, carbon per unit of land, land per capita, and environmental impact per capita effects) influencing CO2es. Thus, to mitigate the country's CO2es efficiently, it is necessary to determine the driving factors of its emissions and damage variations. For this, we use the logarithmic mean Divisia index method. This research decomposes the major two dimensions, such as carbon sources and carbon damage variations from 1986 to 2020, into eight factors. The results show that Pakistan's CO2es increased continuously during the period, with an average annual growth rate of 4.76%. Growing the country's CO2es over 1986-2020, the key influencing factors are economic development, population, and land, while energy intensity and emission factors are the main forces in mitigating CO2es. The carbon source and carbon damage dimensions reached 68.75 Mt and 208.56 Mt, respectively, which led to a rise in CO2e. The entire set of factors is averagely moving around the major outcomes that provide significant policy measures. Finally, to efficiently reduce CO2e, Pakistan should concentrate on specific industrial paths and implement challenging, comprehensive governance to attain a low-carbon chain throughout the process. Thus, based on empirical results, this research put forward policy suggestions for cleaner production to reduce CO2 emissions further, and environmental policies must be tailored to local conditions.

Valorization of food waste derived anaerobic digestate into polyhydroxyalkanoate (PHA) using Thauera mechernichensis TL1

Polyhydroxyalkanoate (PHA) is a biopolymer that can be used as a bioplastic, offering a green alternative to petroleum-based plastics. In this study, we investigated PHA production using Thauera mechernichensis TL1. The optimal molar C/N ratio was determined to be 20 from among the ratios of 4, 20, 40, 80, and 200 and in the absence of nitrogen. Food waste anaerobic digestate, mainly comprised of acetate and propionate, was used as the carbon source for PHA production by T. mechernichensis TL1, resulting in a maximum PHA content of 23.98 ± 0.52 wt% (0.52 ± 0.02 g/L PHA) with a PHA productivity of 0.043 g/L-h PHA. In addition, when using acetate and propionate, T. mechernichensis TL1 produced PHA with a maximum PHA content of 57.43 ± 2.84 wt% (2.04 ± 0.11 g/L PHA) and 50.94 ± 1.61 wt% (2.62 ± 0.16 g/L PHA), with a PHA productivity of 0.092 g/L-h PHA and 0.070 g/L-h PHA, respectively. Proton nuclear magnetic resonance spectroscopy (1H NMR) confirmed polyhydroxybutyrate (PHB) production using acetate as a carbon source, and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) production using propionate or food waste anaerobic digestate as the carbon source. The whole-genome analysis of T. mechernichensis TL1 confirmed the existence of a PHA biosynthesis pathway, with the presence of phaA, phaB, phaC (Class I and Class II), and phaJ genes. This study was the first to demonstrate Thauera sp.'s ability to produce PHA from food waste anaerobic digestate, rendering it as a promising candidate for PHA-producing bacteria for the valorization of food waste.

Effect of plant-self debris on nitrogen removal, transformation and microbial community in mesocosm constructed wetlands planted with Myriophyllum aquaticum

Aquatic macrophytes debris decomposition could release pollutants and nutrients into the water of constructed wetlands (CWs), but their role in nitrogen removal and transformation remains poorly understood. The present study investigated the effects of plant-self debris on nitrogen removal and microbial communities in mesocosm CWs planted with Myriophyllum aquaticum. During the 68-day operation, the plant debris addition did not change the mean removal efficiency of ammonium (NH₄⁺-N) and total nitrogen (TN) of CWs but showed significant differences over the operation time. The NH₄⁺-N and organic nitrogen released from the plant debris decomposition affected the nitrogen removal. The plant debris decreased the effluent nitrate concentration and N₂O emission fluxes of the CWs with the increased abundance of denitrifying bacterial genera, indicating that plant debris decomposition increased the denitrification activities via dissolved organic carbon release. High-throughput sequencing indicated that the plant debris altered the distribution and composition of the microbial community in the sediments. Proteobacteria was the dominant phylum (28-52%), and the relative abundance of denitrifying bacteria genera was significantly higher in the sediments with debris addition (37-40%) than in the non-addition (6.6-7.7%). The present study provided new insights into the role of macrophytes in pollutant removal and the plant management strategy of CWs.

Seasonal variations in acidogenic fermentation of filter primary sludge

Primary treatment of municipal wastewater by rotating belt filtration followed by hydrolysis and acidogenic fermentation of the filter primary sludge (FPS) at ambient temperature was studied at pilot-scale during one year. The seasonal variations of volatile fatty acids (VFAs), nutrient release and soluble COD production as well as microbial community assembly were assessed, leading to novel findings for fermentation at ambient temperature. The reproducibility of VFA production performance was first established by operating the two fermentation reactors under the same conditions, showing similar results regarding VFA production and microbial community structure. One year of operation at 5 d retention time (RT) and 16-29 °C resulted in an average VFA yield of 180±35 mg COD/g VSin and soluble COD yield of 242±40 mg COD/g VSin. The VFA formation was temperature-dependent, with ϴ=1.033±0.005 ( [Formula: see text] . The seasonal variations of the acetic and propionic acid productions were pronounced, whereas the productions of VFAs with longer chains were more stable regardless of temperature. The community structure of the reactor microbiomes was also clearly affected by season and temperature and linked with the production spectrum of VFAs. The ammonium and phosphate releases were stable during the year, leading to a decrease in ratios of soluble COD to NH4+-N and PO43--P during winter. The soluble COD yield was 11% and 27% higher at 5 d RT compared to 3 and 2 d RT respectively, but the corresponding volumetric productivities were lower. The dissimilarities between microbiomes in influent FPS and fermenters were significant even at a short RT of 2 d, and increased with longer RT of 3 and 5 d, primarily caused by selection of bacteria within Bacteroidota in the fermentation reactors.

Selection and validation of reference genes for RT-qPCR gene expression studies in Candida viswanathii cultivated under different grown conditions

The properties presented by Candida viswanathii's lipases turn this specie into a promising producer of potentially applicable lipases in several industrial sectors, such as: food, textiles, in the oleochemical and paper industries, and also in different pharmaceutical applications. However, studies for elucidating growth and developmental processes at the molecular level in this species are still incipient. Performing such kinds of studies often rely on the use of the RT-qPCR, which is a highly sensitivity technique, but whose parameters must be carefully planned for achieving reliable data. Among the crucial parameters required for achieving reliable results through this technique, the use of appropriated and validated reference genes is one the most important, constituting a bottleneck, mainly in species where molecular studies are scarce. Thus, the aim of this study was to determine the best reference genes for RT-qPCR gene expression studies in C. viswanathii grown in culture media containing four different carbon sources (Olive oil, Triolein, Tributyrin, and Glucose). Eleven candidate reference genes (ACT, GPH1, AGL9, RPB2, SAP1, PGK1, TAF10, UBC13, TFC1, UBP6, and FBA1) were analyzed for their expression patterns and stability. Analysis of gene expression stability was performed using the RefFinder tool, which integrates the geNorm, NormFinder, BestKeeper and Delta-Ct algorithms, and validation of the results was performed through analyzing the expression of a lipase gene, CvLIP4. Analyzing the four treatments together, CvACT and CvRPB2 constituted the best reference gene pair. When treatments are analyzed individually, CvRPB2/CvACT, CvFBA1/CvAGL9, CvPGK1/CvAGL9 and CvACT/CvRPB2 were the best reference gene pairs for the culture media containing olive oil, triolein, tributyrin, and glucose as carbon sources, respectively. These results are essential and form the basis for the development of relative gene expression studies in C. viswanathii, since adequate reference genes are crucial for the reliability of RT-qPCR data.

A carbon-neutrality-capactiy index for evaluating carbon sink contributions

The accurate determination of the carbon-neutrality capacity (CNC) of a region is crucial for developing policies related to emissions and climate change. However, a systematic diagnostic method for determining the CNC that considers the rock chemical weathering carbon sink (RCS) is lacking. Moreover, it is challenging but indispensable to establish a fast and practical index model to determine the CNC. Here, we selected Guizhou as the study area, used the methods for different types of carbon sinks, and constructed a CNC index (CNCI) model. We found that: (1) the carbonate rock chemical weathering carbon sink flux was 30.3 t CO₂ km^-2 yr^-1. Guizhou accounted for 1.8% of the land area and contributed 5.4% of the carbonate chemical weathering carbon sink; (2) the silicate rock chemical weathering carbon sink and its flux were 1.44 × 10³ t CO₂ and 2.43 t CO₂ km^-2 yr^-1, respectively; (3) the vegetation-soil ecosystem carbon sink and its flux were 1.37 × 10⁸ t CO₂ and 831.70 t CO₂ km^-2 yr^-1, respectively; (4) the carbon emissions (CEs) were 280 Tg CO₂, about 2.8% of the total for China; and (5) the total carbon sinks in Guizhou were 160 Tg CO₂, with a CNCI of 57%, which is 4.8 times of China and 2.1 times of the world. In summary, we conducted a systematic diagnosis of the CNC considering the RCS and established a CNCI model. The results of this study have a strong implication and significance for national and global CNC determination and gap analysis.

Recovery of electron and carbon source from agricultural waste corncob by microbial electrochemical system to enhance wastewater denitrification

The denitrification process in wastewater treatment plants (WWTPs) is limited by insufficient carbon sources. Agricultural waste corncob was investigated for its feasibility as a low-cost carbon source for efficient denitrification. The results showed that the corncob as the carbon source exhibited a similar denitrification rate (19.01 ± 0.03 gNO₃^--N/m³d) to that of the traditional carbon source sodium acetate (19.13 ± 0.37 gNO₃^--N/m³d). When filling corncob into a microbial electrochemical system (MES) three-dimensional anode, the release of corncob carbon sources was well controlled with an improved denitrification rate (20.73 ± 0.20 gNO₃^--N/m³d). Carbon source and electron recovered from corncob led to autotrophic denitrification and heterotrophic denitrification occurred in the MES cathode, which synergistically improved the denitrification performance of the system. The proposed strategy for enhanced nitrogen removal by autotrophic coupled with heterotrophic denitrification using agricultural waste corncob as the sole carbon source opened up an attractive route for low-cost and safe deep nitrogen removal in WWTPs and resource utilization for agricultural waste corncob.

Improving rhamnolipids production using fermentation-foam fractionation coupling system: cell immobilization and waste frying oil emulsion

This work focused on the development of an inexpensive carbon source and the improvement of the fermentation-foam fractionation coupling system. The rhamnolipids production capacity of waste frying oil (WFO) was evaluated. The suitable bacterial cultivation of seed liquid and the addition amount of WFO was 16 h and 2% (v/v), respectively. A combined strategy of cell immobilization and oil emulsion avoid cell entrainment inside foam and improves the oil mass transfer rate. The immobilization conditions of bacterial cells into alginate-chitosan-alginate (ACA) microcapsules were optimized using the response surface method (RSM). Under the optimal conditions, rhamnolipids production using batch fermentation with immobilized strain reached 7.18 ± 0.23% g/L. WFO was emulsified into a fermentation medium using rhamnolipids as emulsifier (0.5 g/L). By monitoring dissolved oxygen, 30 mL/min was selected as a suitable air volumetric flow rate for fermentation-foam fractionation coupling operation. The total production and recovery percentage of rhamnolipids were 11.29 ± 0.36 g/L and 95.62 ± 0.38%, respectively.

Mycelial biomass and intracellular polysaccharides production, characterization, and activities in Auricularia auricula-judae cultured with different carbon sources

The carbon source, an essential factor for submerged culture, affects fungal polysaccharides production, structures, and activities. This study investigated the impact of carbon sources, including glucose, fructose, sucrose, and mannose, on mycelial biomass and the production, structural characterization, and bioactivities of intracellular polysaccharides (IPS) produced by submerged culture of Auricularia auricula-judae. Results showed that mycelial biomass and IPS production varied with different carbon sources, where using glucose as the carbon source produced the highest mycelial biomass (17.22 ± 0.29 g/L) and IPS (1.62 ± 0.04 g/L). Additionally, carbon sources were found to affect the molecular weight (Mw) distributions, monosaccharide compositions, structural characterization, and activities of IPSs. IPS produced with glucose as the carbon source exhibited the best in vitro antioxidant activities and had the strongest protection against alloxan-damaged islet cells. Correlation analysis revealed that Mw correlated positively with mycelial biomass (r = 0.97) and IPS yield (r = 1.00), while IPS antioxidant activities correlated positively with Mw and negatively with mannose content; the protective activity of IPS was positively related to its reducing power. These findings indicate a critical structure-function relationship for IPS and lay the foundation for utilizing liquid-fermented A. aruicula-judae mycelia and the IPS in functional food production.

Sodium hydroxide or tetramethylammonium hydroxide modified corncob combined with biodegradable polymers to prepare slow-release carbon source for wastewater denitrification

This study proposed a method to improve the bioavailability of artificially prepared carbon sources for the purpose of wastewater denitrification. This carbon source (named SPC) was prepared by mixing corncobs with poly(3-hydroxybutyrate-3-hydroxyvalerate) (PHBV), where the corncobs were pretreated by NaOH or TMAOH. The results of compositional analysis and FTIR showed that both NaOH and TMAOH degraded lignin, hemicellulose and their connection bonds in corncob, thus increased the cellulose content from 39% to 53% and 55%, respectively. The cumulative carbon release from SPC was about 9.3 mg/g and was consistent with both the first-order kinetic and Ritger-Peppas equation. The released organic matters contained low concentration of refractory components. Correspondingly, it showed excellent denitrification performance in simulated wastewater, and the total nitrogen (TN) removal rate was above 95% (influent NO₃^--N was 40 mg/L) and effluent residual chemical oxygen demand (COD) was less than 50 mg/L.

An overlooked soil carbon pool in vegetated coastal ecosystems: National-scale assessment of soil organic carbon stocks in coastal shelter forests of China

Protection and restoration of vegetated coastal ecosystems provide opportunities to mitigate climate change. Coastal shelter forests as one of vegetated coastal ecosystems play vital role on sandy coasts protection, but less attention is paid on their soil organic carbon (OC) sequestration potential. Here, we provide the first national-scale assessment of the soil OC stocks, fractions, sources and accumulation rates from 48 sites of shelter forests and 74 sites of sandy beaches across 22° of latitude in China. We find that, compared with sandy beaches, shelter forest plantation achieves an average soil desalination rate of 92.0 % and reduces the soil pH by 1.3 units. The improved soil quality can facilitate OC sequestration leading to an increase of soil OC stock of 11.8 (0.60-64.2) MgC ha^-1 in shelter forests. Particulate OC (POC) is a dominant OC fraction in both sandy beaches and shelter forests, but most sites are >80 % in shelter forests. The low δ¹³C values and higher C:N ratios, which are more regulated by climate and tree species, together with high POC proportions suggest a substantial contribution of plant-derived OC. Bayesian mixing model indicates that 71.8 (33.5-91.6)% of the soil OC is derived from local plant biomass. We estimate that soil OC stocks in Chinese shelter forests are 20.5 (7.44-79.7) MgC ha^-1 and 4.53 ± 0.71 TgC in the top meter, with an accumulation rate of 45.0 (6.90 to 194.1) gC m^-2 year^-1 and 99.5 ± 44.9 GgC year^-1. According to coastal shelter forest afforestation plan, additional 1.72 ± 0.27 TgC with a rate of 37.9 ± 17.1 GgC year^-1 can be sequestrated in the future. Our findings suggest that construction of coastal shelter forests can be an effective solution to sequester more soil carbon in coastal ecosystems.

Fermentation broth of food waste: A sustainable electron donor for perchlorate biodegradation

Microbial reduction has been considered an effective way to remove perchlorate (ClO₄^-), during which, additional electron donors and carbon sources are required. This work aims to study the potential of fermentation broth of food waste (FBFW) serving as an electron donor for ClO₄^- biodegradation, and further investigates the variance of the microbial community. The results showed that FBFW without anaerobic inoculum at 96 h (F-96) exhibited the highest ClO₄^- removal rate of 127.09 mg/L/d, attributed to higher acetate and lower ammonium contents in the F-96 system. In a 5 L continuous stirred-tank reactor (CSTR), with a 217.39 g/m³·d ClO₄^- loading rate, 100% removal efficiency of ClO₄^- was achieved, indicating that the application of FBFW in the CSTR showed satisfactory performance for ClO₄^- degradation. Moreover, the microbial community analysis revealed that Proteobacteria and Dechloromonas contributed positively to ClO₄^- degradation. Therefore, this study provided a novel approach for the recovery and utilization of food waste, by employing it as a cost-effective electron donor for ClO₄^- biodegradation.

Nitrogen-doped carbon materials prepared using different organic precursors as catalysts of peroxymonosulfate to degrade sulfamethoxazole: First-time performance leading to the incorrect selection of the best catalyst

Nitrogen-doped carbon materials are effective catalysts for peroxymonosulfate (PMS) activation to eliminate organic contaminants. In this research, the activity of nitrogen-doped carbon materials was significantly improved by optimizing the carbon source, and the reusability of the catalyst is used to select the best catalyst instead of depending on the performance in the first use, for avoiding the "short-life" catalyst with great initial activity. Fixing ferric nitrate nonahydrate and melamine as the metal and nitrogen sources, four catalysts were prepared using glucose, glucosamine hydrochloride, dopamine, and trimesic acid as the carbon sources, respectively. Based on the performance in PMS activation for sulfamethoxazole (SMX) removal, in the first use, the activity was Fe-DA-CN (carbon source: dopamine) > Fe-BTC-CN (carbon source: trimesic acid) > Fe-GLU-CN (carbon source: glucosamine) > Fe-DGLU-CN (carbon source: glucose). With no washing for the second time use, the activity was Fe-BTC-CN (0.135 min^-1) ≫ Fe-DA-CN (0.037 min^-1) > Fe-GLU-CN (0.032 min^-1) > Fe-DGLU-CN (0.017 min^-1). The large specific surface area, superior graphitization, and high CO/C-N group content endow Fe-BTC-CN with high ability in PMS activity. Surface-bound radicals are responsible for SMX elimination, and most of the SMX degradation intermediates have lower ecotoxicity than SMX.

Differences in organic nitrogen transformation during chicken manure composting with the addition of different disaccharides

The effect of different carbon sources on nitrogen (N) transformation and N loss through nitrogenous gas volatilization during composting of manure is not clear. Disaccharides had moderate degradation stability compared to monosaccharides and polysaccharides. Therefore, we investigated the effect of adding sucrose (nonreducing sugar) and maltose (reducing sugar) as carbon sources on volatile N loss and hydrolysable organic nitrogen (HON) transformation. HON is composed of bioavailable organic nitrogen (BON) and hydrolysable unknown nitrogen (HUN). Three laboratory-scale experimental groups were conducted with control (CK), 5 % sucrose (SS), and 5 % maltose (MS) addition. Our findings indicated that, while excluding leaching and surface runoff, adding sucrose and maltose decreased the N loss through gas volatilization by 15.78 % and 9.77 %, respectively. The addition of maltose significantly increased the BON content (P < 0.05), which was 6.35 % higher than in CK. The addition of sucrose led to an increase in HUN content (P < 0.05), which was 22.89 % higher than that in CK. In addition, the core microbial communities associated with HON changed after the addition of disaccharides. The transformation of the HON fractions was facilitated by the succession of microbial communities. Ultimately, variation partition analysis (VPA) and structural equation modeling (SEM) verified that the core microbial communities were the major contributors to promoting HON transformation. In summary, adding disaccharides could promote the different transformations of organic nitrogen (ON) and reduce the volatilization of nitrogenous gases by changing the succession of the core microbial communities during composting. This study provided theoretical and technical support for reducing volatile N loss and promoting ON fraction sequestration during composting. Furthermore, the effect of carbon source addition on the nitrogen cycle was also explored.

Application and improvement methods of sludge alkaline fermentation liquid as a carbon source for biological nutrient removal: A review

Alkaline fermentation can reduce the amount of waste activated sludge and prepare sludge alkaline fermentation liquid (SAFL) rich in short-chain fatty acids (SCFAs), which can be used as a high-quality carbon source for the biological nutrient removal (BNR) process. This review compiles the production method of SAFL and the progress of its application as a BNR carbon source. Compared with traditional carbon sources, SAFL has the advantages of higher efficiency and economy, and different operating conditions can influence the yield and structure of SCFAs in SAFL. SAFL can significantly improve the nutrient removal efficiency of the BNR process. Taking SAFL as the internal carbon source of BNR can simultaneously solve the problem of carbon source shortage and sludge treatment difficulties in wastewater treatment plants, and further reduce the operating cost. However, the alkaline fermentation process results in many refractory organics, ammonia and phosphate in SAFL, which reduces the availability of SAFL as a carbon source. Purifying SCFAs by removing nitrogen and phosphorus, directly extracting SCFAs, or increasing the amount of SCFAs in SAFL by co-fermentation or combining with other pretreatment methods, etc., are effective measures to improve the availability of SAFL.

Enhanced heterotrophic nitrification and aerobic denitrification performance of Glutamicibacter arilaitensis EM-H8 with different carbon sources

Different carbon sources for Glutamicibacter arilaitensis EM-H8 were evaluated for ammonium nitrogen (NH₄⁺-N), nitrate nitrogen (NO₃^--N) and nitrite nitrogen (NO₂^--N) removal. Strain EM-H8 could rapidly remove NH₄⁺-N, NO₃^--N and NO₂^--N. The highest removal rates measured for different forms of nitrogen with different carbon sources were 5.94 mg/L/h for NH₄⁺-N with sodium citrate, 4.25 mg/L/h for NO₃^--N with sodium succinate, and 3.88 mg/L/h for NO₂^--N with sucrose. The Nitrogen balance showed that strain EM-H8 could convert 77.88% of the initial nitrogen into nitrogenous gas when NO₂^--N was selected as the sole nitrogen source. The presence of NH₄⁺-N increased the removal rate of NO₂^--N from 3.88 to 4.02 mg/L/h. In an enzyme assay, ammonia monooxygenase, nitrate reductase and nitrite oxidoreductase were detected at 0.209, 0.314, and 0.025 U/mg protein, respectively. These results demonstrate that strain EM-H8 performs well for nitrogen removal, and shows excellent potential for simple and efficient removal of NO₂^--N from wastewater.

Differences in Exudates Between Strains of Chlorella sorokiniana Affect the Interaction with the Microalga Growth-Promoting Bacteria Azospirillum brasilense : Differences in Exudates Between Strains of Chlorella sorokiniana Affect the Interaction with the Microalga Growth-Promoting Bacteria Azospirillum brasilense

The microalga Chlorella sorokiniana and the microalgae growth-promoting bacteria (MGPB) Azospirillum brasilense have a mutualistic interaction that can begin within the first hours of co-incubation; however, the metabolites participating in this initial interaction are not yet identified. Nuclear magnetic resonance (NMR) was used in the present study to characterize the metabolites exuded by two strains of C. sorokiniana (UTEX 2714 and UTEX 2805) and A. brasilense Cd when grown together in an oligotrophic medium. Lactate and myo-inositol were identified as carbon metabolites exuded by the two strains of C. sorokiniana; however, only the UTEX 2714 strain exuded glycerol as the main carbon compound. In turn, A. brasilense exuded uracil when grown on the exudates of either microalga, and both microalga strains were able to utilize uracil as a nitrogen source. Interestingly, although the total carbohydrate content was higher in exudates from C. sorokiniana UTEX 2805 than from C. sorokiniana UTEX 2714, the growth of A. brasilense was greater in the exudates from the UTEX 2714 strain. These results highlight the fact that in the exuded carbon compounds differ between strains of the same species of microalgae and suggest that the type, rather than the quantity, of carbon source is more important for sustaining the growth of the partner bacteria.

Sources and chemical stability of soil organic carbon in natural and created coastal marshes of Louisiana

Coastal marshes are globally important for sequestering carbon, yet sea-level rise and anthropogenic stressors can reduce their capacity as carbon sinks. Marsh restoration can offset a portion of carbon loss through the degradation of natural marshes, but potential differences in the sources and stability of soil organic carbon (SOC) between created and natural marshes may affect their function as a long-term carbon sink. Here, we examine the sources and chemical stability of SOC in natural and created marshes across the Gulf coast of Louisiana, USA. Marshes were examined along an estuarine salinity gradient in a former interdistributary basin of the Mississippi River Delta and in six created marshes across a 32-year chronosequence and a natural reference marsh (n = 6) in the Chenier Plain. Carbon source was assessed using δ¹³C analysis and chemical stability was determined through an acid hydrolysis digestion that removed labile carbon (LC). Soil δ¹³C values suggested that the local vegetation dominated SOC in all natural marshes although brackish marshes had a mix of sources and degradation of SOC. Recalcitrant carbon (RC) was 72.2 ± 0.5 % of SOC across fresh, brackish and saline marshes. The depth-averaged RC accumulation rate was almost three times greater than LC accumulation rate, yet both contributed significantly to accretion and long-term SOC accumulation (124-132 g m^-2 y^-1 in natural marshes). RC and SOC accumulation rate increased with mineral sediment accumulation rate. For the created marshes, SOC became increasingly recalcitrant due to an increase in in-situ plant inputs, but accumulation rates were lower than the natural marshes. Overall, this study illustrates that natural marshes have a large stock of RC from the vegetation while dredge sediment created marshes have no plant-derived carbon initially, which accumulates slowly thereafter. Restoration practices may be improved by preserving and augmenting these deteriorating but carbon-rich natural marshes.

Trehalose transport occurs via TreB in Listeria monocytogenes and it influences biofilm development and acid resistance

Listeria monocytogenes is a pathogenic bacterium that can inhabit a diverse range of environmental niches. This is largely attributed to the high proportion of carbohydrate-specific phosphotransferase system (PTS) genes in its genome. Carbohydrates can be assimilated as sources of energy but additionally they can serve as niche-specific cues for L. monocytogenes to shape its global gene expression, in order to cope with anticipated stresses. To examine carbon source utilization among wild L. monocytogenes isolates and to understand underlying molecular mechanisms, a diverse collection of L. monocytogenes strains (n = 168) with whole genome sequence (WGS) data available was screened for the ability to grow in chemically defined media with different carbon sources. The majority of the strains grew in glucose, mannose, fructose, cellobiose, glycerol, trehalose, and sucrose. Maltose, lactose, and rhamnose supported slower growth while ribose did not support any growth. In contrast to other strains, strain1386, which belonged to clonal complex 5 (CC5), was unable to grow on trehalose as a sole carbon source. WGS data revealed that it carried a substitution (N352K) in a putative PTS EIIBC trehalose transporter, TreB, while this asparagine residue is conserved in other strains in this collection. Spontaneous mutants of strain 1386 that could grow in trehalose were found to harbour a reversion of the substitution in TreB. These results provide genetic evidence that TreB is responsible for trehalose uptake and that the N352 residue is essential for TreB activity. Moreover, reversion mutants also restored other unusual phenotypes that strain 1386 displayed, i.e. altered colony morphology, impaired biofilm development, and reduced acid resistance. Transcriptional analysis at stationary phase with buffered BHI media revealed that trehalose metabolism positively influences the transcription of genes encoding amino acid-based acid resistance mechanisms. In summary, our results demonstrated that N352 is key to the function of the sole trehalose transporter TreB in L. monocytogenes and suggest that trehalose metabolism alters physiology to favour biofilm development and acid stress resistance. Moreover, since strain 1386 is among the strains recommended by the European Union Reference Laboratory for conducting food challenge studies in order to determine whether or not L. monocytogenes can grow in food, these findings have important implications for food safety.

The responses of organic acid production and microbial community to different carbon source additions during the anaerobic fermentation of Chinese cabbage waste

The effects of glucose, fructose, sucrose and molasses on organic acid levels, protein degradation, nutrient preservation and bacteriome were studied during the anaerobic fermentation of Chinese cabbage waste. The results showed that fructose and molasses additions caused a significant (p < 0.05) increase in lactic acid production (82.16-89.79 %), acetic acid production (175.41-196.93 %), ammonia nitrogen formation (15.93-37.43 %) and reduction of neutral detergent fiber level (8.17-15.87 %). However, few positive effects of glucose and sucrose additions were found on organic acid production. Furthermore, carbon source additions enriched (p < 0.05) the acid-producing bacteria, such as Lactobacillus paralimentarius and Lactobacillus heilongjiangensis, upregulated (p < 0.05) the pathways of carbohydrate and lipid metabolisms and reduced (p < 0.05) the abundances of Lactobacillus buchneri and Escherichia coli and bacteria that were mobile elements-contained and stress-tolerant. Collectively, fructose and molasses additions enhanced the recycling of Chinese cabbage waste by anaerobic fermentation, in which the desired products are organic acids.

Improved production of bacterial cellulose by Komagataeibacter europaeus employing fruit extract as carbon source

Bacterial cellulose (BC) has attracted worldwide attention owing to its tremendous properties and versatile applications. BC has huge market demand, however; its production is still limited hence important to explore the economically and technically feasible bioprocess for its improved production. The current study is based on improving the bioprocess for BC production employing Komagataeibacter europeaus 14148. Physico-chemical parameters have been optimized e.g., initial pH, incubation temperature, incubation period, inoculum size, and carbon source for maximum BC production. The study employed crude and/or a defined carbon source in the production medium. Hestrin and Schramm (HS) medium was used for BC production with initial pH 5.5 at 30 °C after 7 days of incubation under static conditions. The yield of BC obtained from fruit juice extracted from orange, papaya, mango and banana were higher than other sugars employed. The maximum BC yield of 3.48 ± 0.16 g/L was obtained with papaya extract having 40 g/L reducing sugar concentration and 3.47 ± 0.05 g/L BC was obtained with orange extract having 40 g/L reducing sugar equivalent in the medium. BC yield was about three-fold higher than standard HS medium. Fruit extracts can be employed as sustainable and economic substrates for BC production to replace glucose and fructose.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13197-022-05451-y.

Changes in the carbon source and storage in a cultivation area of macro-algae in Southeast China

Macro-algae culture has recently attracted attention in China because of its capability to sequester carbon. Here, radionuclides, total organic carbon (TOC), and nitrogen (TN) were examined in a cultivation area of macro-algae in Southeast China. At the reference site, the ratio of TOC to TN (C/N, 8.1 ± 0.2, mean ± SD) did not exhibit discernible variation over the past 70 years. In contrast, in the cultivation area, C/N descended from 9.0 ± 0.2 around 1960 to 8.3 ± 0.2 between 1960 and 1990 and 7.6 ± 0.2 after 1990, coincident with the recorded kelp production in this area, indicating an influence of macro-algae culture-associated activities on carbon origin. Using a model, algal culture-associated activities contributed 23 ± 7 % between 1963 and 1990 and 53 ± 8 % between 1990 and 2022 to TOC. The burial of culture-associated TOC varied from 0.15 to 1.23 mg-C cm^-2 yr^-1, implying the unneglectable influence on carbon storage.

Adding glucose delays the conversion of ethanol and acetic acid to caproic acid in Lacrimispora celerecrescens JSJ-1

Caproic acid is an important fatty acid with diverse applications. In this study, the biomass growth and metabolites of Lacrimispora celerecrescens JSJ-1 were investigated under different carbon sources (ethanol, starch, sucrose, and glucose), with a focus on the effect of the coexistence of glucose and ethanol on the synthesis of caproic acid. The results showed that starch, glucose, and sucrose all contributed to the biomass of L. celerecrescens JSJ-1. Under the three carbon sources, L. celerecrescens JSJ-1 produced acetic acid, butyric acid, lactic acid, ethanol, and butanol, but caproic acid was not produced. Ethanol was the optimal substrate for the production of caproic acid. When glucose and ethanol coexisted, the generation time of caproic acid was delayed compared with that in ethanol sodium acetate medium (ES medium). This was because glucose was preferentially consumed over ethanol. Lactic acid was generated as a result of glucose consumption, which led to a significant decrease in pH from 6.45 to 4.68. The low pH (< 5) inhibited the synthesis of caproic acid. Then, the strain's usage of lactic acid and the reaction between CaCO₃ and lactic acid caused the pH to increase. L. celerecrescens JSJ-1 did not start producing caproic acid using ethanol and acetic acid until the pH increased to 5.8. This research enriches the knowledge regarding the metabolism of L. celerecrescens JSJ-1 and provides guidelines for the industrial production of caproic acid by using L. celerecrescences JSJ-1. KEY POINTS: • Ethanol is the optimal substrate for the synthesis of caproic acid by Lacrimispora celerecrescens JSJ-1. • Lacrimispora celerecrescens JSJ-1 produced lactic acid rapidly when it used glucose, causing a sharp drop in pH. • pH is a crucial factor affecting the synthesis of caproic acid from ethanol by Lacrimispora celerecrescens JSJ-1.

Effect of different carbon sources on sulfate reduction and microbial community structure in bioelectrochemical systems

Microbial electrolysis cells (MECs) have rapidly developed into a promising technology to treat sulfate-rich wastewater that lacks electron donors. Hence, a better understanding of the effect on the microbial community structure caused by different sources in bioelectrochemical systems is required. This study sought to investigate the effect of different carbon sources (NaHCO₃, ethanol, and acetate were employed as sole carbon source respectively) on the performance of sulfate-reducing biocathodes. The sulfate reduction efficiency enhanced by the bioelectrochemical systems was 8.09 - 11.57% higher than that of open-circuit reference experiments. Furthermore, the optimum carbon source was ethanol with a maximum sulfate reduction rate of 170 mg L^-1 d^-1 in the bioelectrochemical systems. The different carbon sources induced significant differences in sulfate reduction efficiency as demonstrated by the application of a micro-electrical field. Microbial community structure and network analysis revealed that all three kinds of carbon source systems enriched large proportions of sulfate-reducing bacteria and electroactive bacteria but were significantly distinct in composition. The dominant sulfate-reducing bacteria that use NaHCO₃ and acetate as carbon sources were Desulfobacter and Desulfobulbus, whereas those that use ethanol as carbon source were Desulfomicrobium and Desulfovibrio. Our results suggest that ethanol is a more suitable carbon source for sulfate reduction in bioelectrochemical systems.

Augmentation in polyhydroxybutyrate and biogas production from waste activated sludge through mild sonication induced thermo-fenton disintegration

In this study, an innovative approach was developed to enhance the hydrolysis through phase-separated pretreatment by removing exopolymeric substances via mild sonication followed by thermo-Fenton disintegration. The exopolymeric substances fragmentation was enhanced at the sonic specific energy input of 2.58 kJ/kg total solids. After exopolymeric substance removal, the disintegration of biomass by thermo-Fenton yield the solubilization of 29.8 % at Fe²⁺:H₂O₂ dosage and temperature of 0.009:0.036 g/g suspended solids and 80 °C as compared to thermo-Fenton alone disintegration. The polyhydroxybutyrate content of 93.1 % was accumulated by Bacillus aryabhattai at the optimum time of 42 h, while providing 70 % (v/v) pre-treated supernatant as a carbon source under nutrient-limiting condition. Moreover, the biogas generation of 0.187 L/g chemical oxygen demand was achieved using settled pretreated sludge. The pretreated sludge sample thus served as a carbon source for polyhydroxybutyrate producers as well as substrate for biogas production.

The characteristics of stepwise ultrasonic hydrolysates of sludge for enhancing denitrification

The disposal of waste activated sludge (WAS) accounts for approximately 60 % of wastewater treatment plant operating costs. In this study, according to the reaction time and water quality parameters, ultrasonic hydrolysis of WAS is divided into three stages, including floc-disintegration (0-25.2 kJ/g TS), cell-disruption (25.2-36 kJ/g TS), and cell-degradation (over 36 kJ/g TS). The results show that more than 70 % carbon distributes inside the cell, which also contains 63.8 % protein enhancing denitrification capacity. Moreover, cell-degradation hydrolysate has a higher proportion of readily biodegradable COD, indicating that intracellular organic matter is more capable of denitrification than extracellular. Therefore, the optimal ultrasonic operating range is E_s = 36-72 kJ/g TS as carbon source, and obtain the hydrolysate with high ratio of soluble chemical oxygen demand to total nitrogen for denitrification. Furthermore, this study supports the comprehensive interpretation of ultrasonic hydrolyzed WAS and the characteristics of hydrolysate as carbon source for enhancing denitrification.

Mechanisms of interaction between polystyrene nanoplastics and extracellular polymeric substances in the activated sludge cultivated by different carbon sources

Nanoplastics (NPs) are ubiquitously present in wastewater treatment plants, which would be removed by the flocculation of extracellular polymeric substances (EPS) from activated sludge. However, the interaction mechanisms between NPs and EPS of activated sludge remain largely unexplored. This study investigated the interaction mechanisms between polystyrene nanoplastics (PS-NPs) and EPS with sodium acetate (NaAc), methanol (MeOH) and glucose (GLC) as carbon sources. The results showed that the functional group involved in the interactions between PS-NPs and EPS was the carbonyl of protein amide I region. The interaction between PS-NPs and EPS increased the β-sheets content, decreased the ratio of α-helix to (β-sheet + random coil), and changed the protein secondary structures to strong rigidity. This enhanced the flocculation of activated sludge cultivated by these three carbon sources. The flocculation between PS-NPs and EPS in activated sludge using NaAc as the carbon source was the strongest among these three carbon sources. Therefore, the degree of flocculation between NPs and EPS of activated sludge in wastewater treatment plants varies with carbon sources. This work provides a reference for the NPs removal mechanisms from wastewater, which will help to understand the migration behavior of MPs and NPs in wastewater treatment processes.

Transcriptome-based Mining of the Constitutive Promoters for Tuning Gene Expression in Aspergillus oryzae

Transcriptional regulation has been adopted for developing metabolic engineering tools. The regulatory promoter is a crucial genetic element for strain optimization. In this study, a gene set of Aspergillus oryzae with highly constitutive expression across different growth stages was identified through transcriptome data analysis. The candidate promoters were functionally characterized in A. oryzae by transcriptional control of β-glucuronidase (GUS) as a reporter. The results showed that the glyceraldehyde triphosphate dehydrogenase promoter (PgpdA1) of A. oryzae with a unique structure displayed the most robust strength in constitutively controlling the expression compared to the PgpdA2 and other putative promoters tested. In addition, the ubiquitin promoter (Pubi) of A. oryzae exhibited a moderate expression strength. The deletion analysis revealed that the 5' untranslated regions of gpdA1 and ubi with the length of 1028 and 811 nucleotides, counted from the putative translation start site (ATG), respectively, could efficiently drive the GUS expression. Interestingly, both promoters could function on various carbon sources for cell growth. Glucose was the best fermentable carbon source for allocating high constitutive expressions during cell growth, and the high concentrations (6-8% glucose, w/v) did not repress their functions. It was also demonstrated that the secondary metabolite gene coding for indigoidine could express under the control of PgpdA1 or Pubi promoter. These strong and moderate promoters of A. oryzae provided beneficial options in tuning the transcriptional expression for leveraging the metabolic control towards the targeted products.

A hormesis-like effect of FeS on heterotrophic denitrification and its mechanisms

To alleviate the insufficiency of carbon source in sewage, many sulfur-containing inorganic electron donors were added into traditional heterotrophic denitrification process. However, the effects of extraneous inorganic electron donors on heterotrophic denitrification were still largely unknown. In this study, a hormesis-like effect of ferrous sulfide (FeS, a representative inorganic electron donors) on Paracoccus denitrificans was observed. Total nitrogen (TN) removal efficiency of P. denitrificans rose by 15% with the increase of FeS dosage from 0 to 0.3 g L^-1 (low level), whereas the TN removal significantly decreased to 53% as the dosage of FeS mounted up to 5.0 g L^-1 (high level). Furthermore, the impacts of FeS on glucose utilization and bacterial growth exhibited hormesis-like effects. A subsequent mechanistic study revealed that above influences were caused by its released ions (Fe²⁺, Fe³⁺, and S^2-) rather than particle size. Further study illustrated that low dosage of FeS released a small amount of Fe²⁺ and Fe³⁺, which provided sufficient electrons via promoting glucose utilization, then improved denitrification. Conversely, FeS with high dosage inhibited denitrification via its released S^2-, which suppressed the activity of key denitrifying enzymes rather than influenced glucose metabolism and electron provision. Our results provide an insight into improving denitrification efficiency of the mixotrophic process coexisting with autotrophic and heterotrophic denitrifiers.

Measuring Niche-Associated Metabolic Activity in Planktonic and Biofilm Bacteria

Most pathobionts of the respiratory tract form biofilms during asymptomatic colonization to survive and persist in this niche. Environmental changes of the host niche, often resulting from infection with respiratory viruses, changes of the microbiota composition, or other host assaults, can result in biofilm dispersion and spread of bacteria to other host niches, resulting in infections, such as otitis media, pneumonia, sepsis, and meningitis. The niches that these bacteria encounter during colonization and infection vary markedly in nutritional availability and contain different carbon sources and levels of other essential nutrients needed for bacterial growth and survival. As these niche-related nutritional variations regulate bacterial behavior and phenotype, a better understanding of bacterial niche-associated metabolic activity is likely to provide a broader understanding of bacterial pathogenesis. In this chapter, we use Streptococcus pneumoniae as a model respiratory pathobiont. We describe methods and models used to grow bacteria planktonically or to form biofilms in vitro by incorporating crucial host environmental factors, including the various carbon sources associated with specific niches, such as the nasopharynx or bloodstream. We then present methods describing how these models can be used to study bacterial phenotypes and their association with metabolic energy production and the generation of fermentation products.