Effect of pyrite particle size on the denitrification performance of autotrophic or split-mixotrophic bioreactors supported by pyrite/polycaprolactone.

In this study, a pyrite-based autotrophic denitrification (PAD) system, a polycaprolactone (PCL)-supported heterotrophic denitrification (PHD) system, and a pyrite+PCL-based split-mixotrophic denitrification (PPMD) system were constructed. The pyrite particle size was controlled in 1-3, 3-5, or 5-8 mm in both the PAD and PPMD systems to investigate the effect of pyrite particle size on the denitrification performance of autotrophic or split-mixotrophic bioreactors. It was found that the PAD system achieved the best denitrification efficiency with an average removal rate of 98.98% in the treatment of 1- to 3-mm particle size, whereas it was only 19.24% in the treatment of 5- to 8-mm particle size. At different phases of the whole experiment, the nitrate removal rates of both the PHD and PPMD systems remained stable at a high level (>94%). Compared with the PAD or PHD system, the PPMD system reduced the concentrations of sulfate and chemical oxygen demand in the final effluent efficiently. The interconnection network diagram explained the intrinsic metabolic pathways of nitrogen, sulfur, and carbon in the three denitrification systems at different phases. In addition, the microbial community analysis showed that the PPMD system was beneficial for the enrichment of Firmicutes. Finally, the impact mechanism of pyrite particle size on the performance of the PPMD system was proposed. PRACTITIONER POINTS: The reduction of pyrite particle size was beneficial for improving the efficiency of the PAD process. The change in particle size had an effect on NO2 --N accumulation in the PAD system. The accumulation of NH4 +-N in the PPMD system increased with the decrease in particle size. The reduction of pyrite particle size increased the production of SO4 2- in the PAD and PPMD systems. The correlations among the effluent indicators of the PAD and PPMD systems could be well explained.

Shift in microorganism and functional gene abundance during completely autotrophic nitrogen removal over nitrite (CANON) process.

Nitrification-denitrification process has failed to meet wastewater treatment standards. The completely autotrophic nitrite removal (CANON) process has a huge advantage in the field of low carbon/nitrogen wastewater nitrogen removal. However, slow start-up and system instability limit its applications. In this study, the time of the start-up CANON process was reduced by using bio-rope as loading materials. The establishing of graded dissolved oxygen improved the stability of the CANON process and enhanced the stratification effect between functional microorganisms. Microbial community structure and the abundance of nitrogen removal functional genes are also analyzed. The results showed that the CANON process was initiated within 75 days in the complete absence of anaerobic ammonium oxidizing bacteria (AnAOB) inoculation. The ammonium and nitrogen removal efficiencies of CANON process reached to 94.45% and 80.76% respectively. The results also showed that the relative abundance of nitrogen removal bacterial in the biofilm gradually increases with the dissolved oxygen content in the solution decreases. In contrast, the relative abundance of ammonia oxidizing bacteria was positively correlated with the dissolved oxygen content in the solution. The relative abundance of g__Candidatus_Brocadia in biofilm was 15.56%, and while g__Nitrosomonas was just 0.6613%. Metagenomic analysis showed that g__Candidatus_Brocadia also contributes 66.37% to the partial-nitrification functional gene Hao (K10535). This study presented a new idea for the cooperation between partial-nitrification and anammox, which improved the nitrogen removal system stability.

Autotrophic denitrification by sulfur-based immobilized electron donor for enhanced nitrogen removal: Denitrification performance, microbial interspecific interaction and functional traits.

Sulfur-driven autotrophic denitrification (SdAD) is a promising nitrogen removing process, but its applications were generally constrained by conventional electron donors (i.e., thiosulfate (Na2S2O3)) with high valence and limited bioavailability. Herein, an immobilized electron donor by loading elemental sulfur on the surface of polyurethane foam (PFSF) was developed, and its feasibility for SdAD was investigated. The denitrification efficiency of PFSF was 97.3%, higher than that of Na2S2O3 (91.1%). Functional microorganisms (i.e., Thiobacillus and Sulfurimonas) and their metabolic activities (i.e., nir and nor) were substantially enhanced by PFSF. PFSF resulted in the enrichment of sulfate-reducing bacteria, which can reduce sulfate (SO42-). It attenuated the inhibitory effect of SO42-, whereas the generated product (hydrogen sulfide) also served as an electron donor for SdAD. According to the economic evaluation, PFSF exhibited strong market potential. This study proposes an efficient and low-cost immobilized electron donor for SdAD and provides theoretical support to its practical applications.

Evaluation of autotrophic process influencing extracellular polymeric substances in aerobic membrane bioreactor with expanded ASM model.

A mathematical model was developed to predict the formation of both the autotrophic and heterotrophic extracellular polymeric substances (EPS) in the aerobic membrane bioreactor (MBR). Batch experimental results and 45-day operation data on a pilot MBR at a sludge retention time (SRT) of 20 d were used to calibrate and validate the model. Simulated MBR setup results demonstrated the key role of the influent COD and NH4+-N in governing the composition of heterotrophic and autotrophic EPS in the MBR. These results also revealed that the autotrophic EPS process was non-ignorable in the system. According to the autotrophic EPS simulation in the MBR, the EPS yield increased with increasing influent COD/NH4+-N ratio towards a constant level. The EPS yield was significantly influenced by the SRT, attributed to the autotrophic process's impact on EPS. Simulation results revealed a slight increase in EPS yield with an SRT of up to 5 days, followed by a rapid decrease beyond that threshold.

Amorphous Fe substrate enhances nitrogen and phosphorus removal in sulfur autotrophic process.

The autotrophic denitrification of coupled sulfur and natural iron ore can remove nitrogen and phosphorus from wastewater with low C/N ratios. However, the low solubility of crystalline Fe limits its bioavailability and P absorption capacity. This study investigated the effects of amorphous Fe in drinking water treatment residue (DWTR) and crystalline Fe in red mud (RM) on nitrogen and phosphorus removal during sulfur autotrophic processes. Two types of S-Fe cross-linked filler particles with three-dimensional mesh structures were obtained by combining sulfur with the DWTR/RM using the hydrogel encapsulation method. Two fixed-bed reactors, sulfur-DWTR autotrophic denitrification (SDAD) and sulfur-RM autotrophic denitrification (SRAD), were constructed and stably operated for 236 d Under a 5-8-h hydraulic retention time, the average NO3--N, TN, and phosphate removal rates of SDAD and SRAD were 99.04 %, 96.29 %, 94.03 % (SDAD) and 97.33 %, 69.97 %, 82.26 % (SRAD), respectively. It is important to note that fermentative iron-reducing bacteria, specifically Clostridium_sensu_stricto_1, were present in SDAD at an abundance of 58.17 %, but were absent from SRAD. The presence of these bacteria facilitated the reduction of Fe (III) to Fe (II), which led to the complete denitrification of the S-Fe (II) co-electron donor to produce Fe (III), completing the iron cycle in the system. This study proposes an enhancement method for sulfur autotrophic denitrification using an amorphous Fe substrate, providing a new option for the efficient treatment of low-C/N wastewater.

Electrochemical-coupled sulfur-driven autotrophic denitrification for nitrogen removal from raw landfill leachate: Evaluation of performance and mechanisms.

The cost-effective and environment-friendly sulfur-driven autotrophic denitrification (SdAD) process has drawn significant attention for advanced nitrogen removal from low carbon-to-nitrogen (C/N) ratio wastewater in recent years. However, achieving efficient nitrogen removal and maintaining system stability of SdAD process in treating low C/N landfill leachate treatment have been a major challenge. In this study, a novel electrochemical-coupled sulfur-driven autotrophic denitrification (ESdAD) system was developed and compared with SdAD system through a long-term continuous study. Superior nitrogen removal performance (removal efficiency of 89.1 ± 2.5 %) was achieved in ESdAD system compared to SdAD process when treating raw landfill leachate (influent total nitrogen (TN) concentration of 241.7 ± 36.3 mg-N/L), and the effluent TN concentration of ESdAD bioreactor was as low as 24.8 ± 5.1 mg-N/L, which meets the discharge standard of China (< 40 mg N/L). Moreover, less sulfate production rate (1.3 ± 0.2 mg SO42--S/mgNOx--N vs 1.7 ± 0.2 mg SO42--S/mgNOx--N) and excellent pH modulation (pH of 6.9 ± 0.2 vs 5.8 ± 0.4) were also achieved in the ESdAD system compared to SdAD system. The improvement of ESdAD system performance was contributed to coexistence and interaction of heterotrophic bacteria (e.g., Rhodanobacter, Thermomonas, etc.), sulfur autotrophic bacteria (e.g., Thiobacillus, Sulfurimonas, Ignavibacterium etc.) and hydrogen autotrophic bacteria (e.g., Thauera, Comamonas, etc.) under current stimulation. In addition, microbial nitrogen metabolic activity, including functional enzyme (e.g., Nar and Nir) activities and electron transfer capacity of extracellular polymeric substances (EPS) and cytochrome c (Cyt-C), were also enhanced during current stimulation, which facilitated the nitrogen removal and maintained system stability. These findings suggested that ESdAD is an effective and eco-friendly process for advanced nitrogen removal for low C/N wastewater.

Enhancing nitrogen removal in the partial denitrification/anammox processes for SO4- - Rich wastewater treatment: Insights into autotrophic and mixotrophic strategies.

The investigation of partial denitrification/anammox (PD/anammox) processes was conducted under autotrophic (N-S cycle) and mixotrophic (N-S-C cycle) conditions over 180 days. Key findings revealed the remarkable capability of SO42--dependent systems to produce NO2- effectively, supporting anaerobic NH4+ oxidation. Additionally, SO42- served as an additional electron acceptor in sulfate reduction ammonium oxidation (SRAO). Increasing influent SO42- concentrations notably improved ammonia utilization rates (AUR) and NH4+ and total nitrogen (TN) utilization efficiencies, peaking at 57% for SBR1 and nearly 100% for SBR2. Stoichiometric analysis showed a 7.5-fold increase in AUR (SRAO and anammox) in SBR1 following SO42- supplementation. However, the analysis for SBR2 indicated a shift towards SRAO and mixotrophic denitrification, with anammox disappearing entirely by the end of the study. Comparative assessments between SBR1 and SBR2 emphasized the impact of organic compounds (CH3COONa) on transformations within the N-S-C cycle. SBR1 performance primarily involved anammox, SRAO and other SO42- utilization pathways, with minimal S-dependent autotrophic denitrification (SDAD) involvement. In contrast, SBR2 performance encompassed SRAO, mixotrophic denitrification, and other pathways for SO42- production. The SRAO process involved two dominant genera, such as Candidatus Brocadia and PHOS-HE36.

Biodiversity of autotrophic euglenids based on the group specific DNA metabarcoding approach.

This study reports a comprehensive analysis of photoautotrophic euglenids' distribution and biodiversity in 16 small water bodies of various types (including fish ponds, field ponds, rural ponds and park ponds) located in three regions of Poland: Masovia, Masuria and Pomerania during a period of three years. By employing a euglenid specific barcode marker and a curated database of V2 18S rDNA sequences it was possible to identify 97.7 % of euglenid reads at species level. A total of 152 species classified in 13 genera were identified. The number of euglenid species found in one pond varied from 40 to 102. The most common species were Euglena agilis and Euglenaria caudata, found in every analysed waterbody. The highest number of observed species belonged to Trachelomonas and Phacus. Certain species exhibited a tendency to coexist, suggesting the presence of distinct species assemblages. Among them, the most distinctive cluster was associated with water bodies located in the Masuria region, characterized also by the greatest species richness, including many very rare species: Euglenaformis chlorophoenicea, Lepocinclis autumnalis, L. marssonii, Trachelomonas eurystoma, T. manschurica, T. mucosa, T. zuberi, T. zuberi var. nepos.

Biological carbon capture from biogas streams: Insights into Cupriavidus necator autotrophic growth and transcriptional profile.

Recycling carbon-rich wastes into high-value platform chemicals through biological processes provides a sustainable alternative to petrochemicals. Cupriavidus necator, known for converting carbon dioxide (CO2) into polyhydroxyalkanoates (PHA) was studied for the first time using biogas streams as the sole carbon source. The bacterium efficiently consumed biogenic CO2 from raw biogas with methane at high concentrations (50%) proving non-toxic. Continuous addition of H2 and O2 enabled growth trends comparable to glucose-based heterotrophic growth. Transcriptomic analysis revealed CO2-adaptated cultures exhibited upregulation of hydrogenases and Calvin cycle enzymes, as well as genes related to electron transport, nutrient uptake, and glyoxylate cycle. Non-adapted samples displayed activation of stress response mechanisms, suggesting potential lags in large-scale processes. These findings showcase the setting of growth parameters for a pioneering biological biogas upgrading strategy, emphasizing the importance of inoculum adaptation for autotrophic growth and providing potential targets for genetic engineering to push PHA yields in future applications.

Heterotrophic and autotrophic production of L-isoleucine and L-valine by engineered Cupriavidus necator H16.

Advancement in commodity chemical production from carbon dioxide (CO2) offers a promising path towards sustainable development goal. Cupriavidus necator is an ideal host to convert CO2 into high-value chemicals, thereby achieving this target. Here, C. necator was engineered for heterotrophic and autotrophic production of L-isoleucine and L-valine. Citramalate synthase was introduced to simplify isoleucine synthesis pathway. Blocking poly-hydroxybutyrate biosynthesis resulted in significant accumulation of isoleucine and valine. Besides, strategies like key enzymes screening and overexpressing, reducing power balancing and feedback inhibition removing were applied in strain modification. Finally, the maximum isoleucine and valine titers of the best isoleucine-producing and valine-producing strains reached 857 and 972 mg/L, respectively, in fed-batch fermentation using glucose as substrate, and 105 and 319 mg/L, respectively, in autotrophic fermentation using CO2 as substrate. This study provides a feasible solution for developing C. necator as a microbial factory to produce amino acids from CO2.

The effect of reflux ratio on sulfur disproportionation tendency in anaerobic baffled reactor with the heterotrophic combining sulfur autotrophic processes under high concentration perchlorate stress.

In a laboratory scale, an anaerobic baffled reactor (ABR) consisting of eight compartments, the heterotrophic combining sulfur autotrophic processes under different reflux ratios were constructed to achieve effective perchlorate removal and alleviate sulfur disproportionation reaction. Perchlorate was efficiently removed with effluent perchlorate concentration below 0.5 µg/L when the influent perchlorate concentration was 1030 mg/L during stages I ~ V, indicating that heterotrophic combining sulfur autotrophic perchlorate reduction processes can effectively achieve high concentration perchlorate removal. Furthermore, the 100% reflux ratio could reduce the contact time between sulfur particles and water; thus, the sulfur disproportionation reaction was inhibited. However, the inhibition effect of reflux on sulfur disproportionation was attenuated due to dilute perchlorate concentration when a reflux ratio of 150% and 200% was implemented. Meanwhile, the content of extracellular polymeric substances (EPS) in the heterotrophic unit (36.79 ~ 45.71 mg/g VSS) was higher than that in the sulfur autotrophic unit (22.19 ~ 25.77 mg/g VSS), indicating that high concentration perchlorate stress in the heterotrophic unit promoted EPS secretion. Thereinto, the PN content of sulfur autotrophic unit decreased in stage III and stage V due to decreasing perchlorate concentration in the autotrophic unit. Meanwhile, the PS content increased with increasing reflux in the autotrophic unit, which was conducive to the formation of biofilm. Furthermore, the high-throughput sequencing result showed that Proteobacteria, Chloroflexi, Firmicutes, and Bacteroidetes were the dominant phyla and Longilinea, Diaphorobacter, Acinetobacter, and Nitrobacter were the dominant genus in ABR, which were associated with heterotrophic or autotrophic perchlorate reduction and beneficial for effective perchlorate removal. The study indicated that reflux was a reasonable strategy for alleviating sulfur disproportionation in heterotrophic combining sulfur autotrophic perchlorate removal processes.

Improved efficiency and stability using a novel elemental sulfur-based moving-bed denitrification process.

Elemental sulfur-based denitrification (ESDeN) technology is known as a cost-saving alternative to its heterotrophic counterpart for nutrient removal from organic-deficient water. However, the traditional fixed-bed reactor (FixBR), as an extensively used process, suffers from a low denitrification rate and even performance deterioration during long-term operation. Herein, we proposed a novel elemental sulfur-based denitrifying moving-bed reactor (ESDeN-MovBR), in which a screw rotator was employed to drive the filled sulfur particles to be microfluidized vertically (a state of vertical-loop movement). Our results showed that the ESDeN-MovBR realized much superior and more stable denitrification performance compared to the ESDeN-FixBR, as indicated by 3.09-fold higher denitrification rate and over one order of magnitude lower intermediates (NO2- and N2O) yield, which could last for over 100 days. Further research revealed that the microfluidization of sulfur particles facilitated the expelling of nitrogen bubbles and excessive biomass, resulting in the prolongation of actual hydraulic retention time by over 80 % and could partially explain the higher denitrification rate in ESDeN-MovBR. The remaining contribution to the improvement of denitrification rate was suggested to be result from changes in biofilm properties, in which the biofilm thickness of ESDeN-MovBR was found to be 3.29 times thinner yet enriched with 2.52 times more autotrophic denitrifiers. This study offered a completely new solution to boost up the denitrification performance of ESDeN technology and provided in-depth evidence for the necessity of biofilm thickness control in such technology.

Autotrophic growth of Escherichia coli is achieved by a small number of genetic changes.

Synthetic autotrophy is a promising avenue to sustainable bioproduction from CO2. Here, we use iterative laboratory evolution to generate several distinct autotrophic strains. Utilising this genetic diversity, we identify that just three mutations are sufficient for Escherichia coli to grow autotrophically, when introduced alongside non-native energy (formate dehydrogenase) and carbon-fixing (RuBisCO, phosphoribulokinase, carbonic anhydrase) modules. The mutated genes are involved in glycolysis (pgi), central-carbon regulation (crp), and RNA transcription (rpoB). The pgi mutation reduces the enzyme's activity, thereby stabilising the carbon-fixing cycle by capping a major branching flux. For the other two mutations, we observe down-regulation of several metabolic pathways and increased expression of native genes associated with the carbon-fixing module (rpiB) and the energy module (fdoGH), as well as an increased ratio of NADH/NAD+ - the cycle's electron-donor. This study demonstrates the malleability of metabolism and its capacity to switch trophic modes using only a small number of genetic changes and could facilitate transforming other heterotrophic organisms into autotrophs.

Meta-analyzing the mechanism of pyrogenic biochar strengthens nitrogen removal performance in sulfur-driven autotrophic denitrification system: Evidence from metatranscriptomics.

Sulfur-driven autotrophic denitrification (SAD) exhibits significant benefits in treating low carbon/nitrogen wastewater. This study presents an eco-friendly, cost-effective, and highly efficient method for enhancing nitrogen removal performance. The addition of biochar prepared at 300 °C (BC300) notably increased nitrogen removal efficiency by 31.60 %. BC300 concurrently enhanced electron production, the activities of the electron transfer system, and electron acceptors. With BC300, the ratio of NADH/NAD+ rose 2.00±0.11 times compared to without biochar, and the expression of NAD(P)H dehydrogenase genes was markedly up-regulated. In the electron transfer system, BC300 improved the electroactivity of extracellular polymeric substances and the activities of NADH dehydrogenase and complex III in intracellular electron transfer. Subsequently, electrons were directed into denitrification enzymes, where the nar, nir, nor, and nos related genes were highly expressed with BC300 addition. Significantly, BC300 activated the Clp and quorum sensing systems, positively influencing numerous gene expressions and microbial communication. Furthermore, the O%, H%, molar O/C, and aromaticity index in biochar were identified as crucial bioavailable parameters for enhancing nitrogen removal in the SAD process. This study not only confirms the application potential of biochar in SAD, but also advances our comprehension of its underlying mechanisms.

Mesophotic corals in Hawai'i maintain autotrophy to survive low-light conditions.

In mesophotic coral ecosystems, reef-building corals and their photosynthetic symbionts can survive with less than 1% of surface irradiance. How depth-specialist corals rely upon autotrophically and heterotrophically derived energy sources across the mesophotic zone remains unclear. We analysed the stable carbon (δ13C) and nitrogen (δ15N) isotope values of a Leptoseris community from the 'Au'au Channel, Maui, Hawai'i (65-125 m) including four coral host species living symbiotically with three algal haplotypes. We characterized the isotope values of hosts and symbionts across species and depth to compare trophic strategies. Symbiont δ13C was consistently 0.5‰ higher than host δ13C at all depths. Mean colony host and symbiont δ15N differed by up to 3.7‰ at shallow depths and converged at deeper depths. These results suggest that both heterotrophy and autotrophy remained integral to colony survival across depth. The increasing similarity between host and symbiont δ15N at deeper depths suggests that nitrogen is more efficiently shared between mesophotic coral hosts and their algal symbionts to sustain autotrophy. Isotopic trends across depth did not generally vary by host species or algal haplotype, suggesting that photosynthesis remains essential to Leptoseris survival and growth despite low light availability in the mesophotic zone.

Optimization of operating parameters and microbiological mechanism of a low C/N wastewater treatment system dominated by iron-dependent autotrophic denitrification.

Ferrous iron (Fe2+) reduces the amount of external carbon source used for the denitrification of low-C/N wastewater. The effects of key operating parameters on the efficiency of ferrous-dependent autotrophic denitrification (FDAD) and the functioning mechanism of the microbiome can provide a regulatory strategy for improving the denitrification efficiency of low C/N wastewater. In this study, the response surface method (RSM) was used to explore the influence of four important parameters-the molar ratio of Fe2+ to NO3--N (Fe/N), total organic carbon (TOC), the molar ratio of inorganic carbon to NO3--N (IC/N) and sludge volume (SV, %)-on the FDAD efficiency. Functional prediction and molecular ecological networks based on high-throughputs sequencing techniques were used to explore changes in the structure, function, and biomarkers of the sludge microbial community. The results showed that Fe/N and TOC were the main parameters affecting FDAD efficiency. Higher concentrations of TOC and high Fe/N ratios provided more electron donors and improved denitrification efficiency, but weakened the importance of biomarkers (Rhodanobacter, Thermomonas, Comamonas, Thauera, Geothrix and unclassified genus of family Gallionellaceae) in the sludge ecological network. When Fe/N > 4, the denitrification efficiency fluctuated significantly. Functional prediction results indicated that genes that dominated N2O and NO reduction and the genes that dominated Fe2+ transport showed a slight decrease in abundance at high Fe/N levels. In light of these findings, we recommend the following optimization ranges of parameters: Fe/N (3.5-4); TOC/N (0.36-0.42); IC/N (3.5-4); and SV (approximately 35%).

Widespread dissolved inorganic carbon-modifying toolkits in genomes of autotrophic Bacteria and Archaea and how they are likely to bridge supply from the environment to demand by autotrophic pathways.

Using dissolved inorganic carbon (DIC) as a major carbon source, as autotrophs do, is complicated by the bedeviling nature of this substance. Autotrophs using the Calvin-Benson-Bassham cycle (CBB) are known to make use of a toolkit comprised of DIC transporters and carbonic anhydrase enzymes (CA) to facilitate DIC fixation. This minireview provides a brief overview of the current understanding of how toolkit function facilitates DIC fixation in Cyanobacteria and some Proteobacteria using the CBB and continues with a survey of the DIC toolkit gene presence in organisms using different versions of the CBB and other autotrophic pathways (reductive citric acid cycle, Wood-Ljungdahl pathway, hydroxypropionate bicycle, hydroxypropionate-hydroxybutyrate cycle, and dicarboxylate-hydroxybutyrate cycle). The potential function of toolkit gene products in these organisms is discussed in terms of CO2 and HCO3- supply from the environment and demand by the autotrophic pathway. The presence of DIC toolkit genes in autotrophic organisms beyond those using the CBB suggests the relevance of DIC metabolism to these organisms and provides a basis for better engineering of these organisms for industrial and agricultural purposes.

Cooperation between autotrophic and heterotrophic denitrifiers under low C/N ratios revealed by individual-based modelling.

Denitrifying biofilms, in which autotrophic denitrifiers (AD) and heterotrophic denitrifiers (HD) coexist, play a crucial role in removing nitrate from water or wastewater. However, it is difficult to elucidate the interactions between HD and AD through sequencing-based experimental methods. Here, we developed an individual-based model to describe the interspecies dynamics and priority effects between sulfur-based AD (Thiobacillus denitrificans) and HD (Thauera phenylcarboxya) under different C/N ratios. In test I (coexistence simulation), AD and HD were initially inoculated at a ratio of 1:1. The simulation results showed excellent denitrification performance and a coaggregation pattern of denitrifiers, indicating that cooperation was the predominant interaction at a C/N ratio of 0.25 to 1.5. In test II (invasion simulation), in which only one type of denitrifier was initially inoculated and the other was added at the invasion time, denitrifiers exhibited a stratification pattern in biofilms. When HD invaded AD, the final HD abundance decreased with increasing invasion time, indicating an enhanced priority effect. When AD invaded HD, insufficient organic carbon sources weakened the priority effect by limiting the growth of HD populations. This study reveals the interaction between autotrophic and heterotrophic denitrifiers, providing guidance for optimizing wastewater treatment process.

Thermodynamic Inhibition of Microbial Sulfur Disproportionation in a Multisubunit Designed Sulfur-Siderite Packed Bioreactor.

Sulfur disproportionation (S0DP) poses a challenge to the robust application of sulfur autotrophic denitrification due to unpredictable sulfide production, which risks the safety of downstream ecosystems. This study explored the S0DP occurrence boundaries with nitrate loading and temperature effects. The boundary values increased with the increase in temperature, exhibiting below 0.15 and 0.53 kg-N/m3/d of nitrate loading at 20 and 30 °C, respectively. A pilot-scale sulfur-siderite packed bioreactor (150 m3/d treatment capacity) was optimally designed with multiple subunits to dynamically distribute the loading of sulfur-heterologous electron acceptors. Operating two active and one standby subunit achieved an effective denitrification rate of 0.31 kg-N/m3/d at 20 °C. For the standby subunit, involving oxygen by aeration effectively transformed the facultative S0DP functional community from S0DP metabolism to aerobic respiration, but with enormous sulfur consumption resulting in ongoing sulfate production of over 3000 mg/L. Meanwhile, acidification by the sulfur oxidation process could reduce the pH to as low as 2.5, which evaluated the Gibbs free energy (ΔG) of the S0DP reaction to +2.56 kJ, thermodynamically suppressing the S0DP occurrence. Therefore, a multisubunit design along with S0DP inhibition strategies of short-term aeration and long-term acidification is suggested for managing S0DP in various practical sulfur-packed bioreactors.

Dominance of net autotrophy in arid landscape low relief polar lakes, Nunavut, Canada.

The Arctic is the fastest warming biome on the planet, and environmental changes are having striking effects on freshwater ecosystems that may impact the regional carbon cycle. The metabolic state of Arctic lakes is often considered net heterotrophic, due to an assumed supply of allochthonous organic matter that supports ecosystem respiration and carbon mineralization in excess of rates of primary production. However, lake metabolic patterns vary according to regional climatic characteristics, hydrological connectivity, organic matter sources and intrinsic lake properties, and the metabolism of most Arctic lakes is unknown. We sampled 35 waterbodies along a connectivity gradient from headwater to downstream lakes, on southern Victoria Island, Nunavut, in an area characterized by low precipitation, organic-poor soils, and high evaporation rates. We evaluated whether lakes were net autotrophic or heterotrophic during the open water period using an oxygen isotopic mass balance approach. Most of the waterbodies were autotrophic and sites of net organic matter production or close to metabolic equilibrium. Autotrophy was associated with higher benthic primary production, as compared to its pelagic counterpart, due to the high irradiance reaching the bottom and efficient internal carbon and nutrient cycling. Highly connected midstream and downstream lakes showed efficient organic matter cycling, as evidenced by the strong coupling between gross primary production (GPP) and ecosystem respiration, while decoupling was observed in some headwater lakes with significantly higher GPP. The shallow nature of lakes in the flat, arid region of southern Victoria Island supports net autotrophy in most lakes during the open water season. Ongoing climate changes that lengthen the ice-free irradiance period and increase rates of nutrient evapoconcentration may further promote net autotrophy, with uncertain long-term effects for lake functioning.