Recalcitrant Molecules Research Articles

Molecular insights into the degradation of organic matter from secondary swine wastewater effluent: A comparative study of advanced oxidation processes

Advanced oxidation processes (AOPs) are promising for the treatment of secondary swine wastewater effluents, however, the molecular-level understanding of effluent organic matter (EfOM) removal and transformation during AOPs is limited. This study employed molecular-level characterization based on Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) and bulk characterizations to investigate these processes in various AOPs, including Cu-Fenton, UV-Cu-Fenton, Fenton, UV-Fenton, and UV/H2O2 treatments. Our findings revealed that the removal rates of dissolved organic carbon and EfOM molecules follow the sequence of UV-Fenton > Fenton > UV-Cu-Fenton > UV/H2O2 > Cu-Fenton, correlating with the rates of H2O2 decomposition during reactions. AOPs with faster H2O2 decomposition, indicative of higher reactive oxygen species generation, predominantly mineralize rather than transform EfOM. Linkage analysis highlighted oxygen addition and deamination as the primary transformation reactions, with variations in the dominance levels of these reactions across different AOPs. Recalcitrant molecule, particularly CHNO and CHO types, including low-molecular-weight carboxyl-rich alicyclic molecules, pose challenges in treatment. To enhance the efficacy of secondary effluent treatment, strategies focusing on the targeted removal of such recalcitrant EfOM should be developed. This study provided new insights into the selection and optimization of AOPs for secondary swine wastewater effluent treatment.

Waste Biomass Pretreatments for Biogas Yield Optimization and for the Extraction of Valuable High-Added-Value Products: Possible Combinations of the Two Processes toward a Biorefinery Purpose

Second- and third-generation biorefineries enable the sustainable management of biomasses within the framework of circular economy principles. This approach aims to minimize waste biomass while generating high-value molecules and bio-energy, such as biogas. Biogas production is achieved via anaerobic digestion, a process where microorganisms metabolize organic compounds in the absence of oxygen to primarily produce CO2 and CH4. The efficiency of this process is closely linked to the composition of the biomass and, sometimes, characteristics of the initial matrix can impede the process. To address these challenges, various pretreatments are employed to enhance digestion efficiency and mitigate issues associated with biomass complexity. However, the implementation of pretreatments can be energy-intensive and costly. The extraction of valuable molecules from biomass for various applications can represent a form of pretreatment. This extraction process selectively removes recalcitrant molecules such as lignin and cellulose, which can hinder biodegradation, thereby adding new value to the biomass. These extracted molecules not only contribute to improved anaerobic digestion efficiency but also offer potential economic benefits by serving as valuable inputs across diverse industrial sectors. This article presents a detailed state of the art of the most widespread biomass pretreatments and specifies when biomass is pretreated to improve the biogas yield and, in contrast, when it is treated to extract high-added-value products. Finally, in order to define if the same treatment can be simultaneously applied for both goals, an experimental section was dedicated to the production of biogas from untreated olive mill wastewater and the same biomass after being freeze-dried and after the extraction of polyphenols and flavonoids. The use of pretreated biomass effectively improved the biogas production yield: the untreated olive mill wastewater led to the production of 147 mL of biogas, while after freeze-drying and after polyphenols/flavonoids extraction, the production was, respectively, equal to 169 mL and 268 mL of biogas.

Spectroscopic and microscopic characterization of humic acids from composts made by co-composting of green waste, spent coffee and OMWW sludge

ABSTRACT Due to its important role in the formation of humic acids (HA), improving lignin degradation during composting has usually been considered a challenge. One practice that could stimulate the biodegradation of this recalcitrant molecule is inoculation with exogenous lignolytic fungal strains. Two composts (C1) and (C2) from piles (H1) and (H2) were evaluated. H1 was the control pile and H2 was inoculated at maturity with Trametes trogii, resulting in a 35% increase in lignin degradation rate compared to H1. The aim of this study was to show the main effects of this increase on the humification process in the co-composting of green waste, coffee grounds and olive mill wastewater sludge (OMWWs). Microstructure of HA1 and HA2 extracted from C1 and C2, respectively, was also investigated by scanning electron microscopy (SEM) and SEM coupled with energy-dispersive X-ray spectroscopy (X-EDS). The results showed that there were several similarities between the compost samples tested. These included the mineral content, the degree of polymerization (PD)> 1 and the compact and rigid surface of the extracted HA. However, C2 was characterized by a higher humic content (HC), degree of polymerization (PD), humification index (HI) and percentage of humic acids (PHA) than C1. Carbon-13 nuclear magnetic resonance (13C-NMR) and Fourier transmission-infrared spectroscopy (FTIR) analysis showed that aliphatic groups such as hydroxyls, alcohols and carboxyls were predominant in both composts. SEM analysis in conjunction with X-EDS analysis of HA2 showed a higher proportion of carbon and potassium (18 and 7.93%) than in HA1 (14 and 0.95%).

Pollutant profile complexity governs wastewater removal of recalcitrant pharmaceuticals.

Organic pollutants are an increasing threat for wildlife and humans. Managing their removal is however complicated by the difficulties in predicting degradation rates. In this work, we demonstrate that the complexity of the pollutant profile, the set of co-existing contaminants, is a major driver of biodegradation in wastewater. We built representative assemblages out of one to five common pharmaceuticals (caffeine, atenolol, paracetamol, ibuprofen, and enalapril) selected along a gradient of biodegradability. We followed their individual removal by wastewater microbial communities. The presence of multichemical background pollution was essential for the removal of recalcitrant molecules such as ibuprofen. High-order interactions between multiple pollutants drove removal efficiency. We explain these interactions by shifts in the microbiome, with degradable molecules such as paracetamol enriching species and pathways involved in the removal of several organic pollutants. We conclude that pollutants should be treated as part of a complex system, with emerging pollutants potentially showing cascading effects and offering leverage to promote bioremediation.

Potential for the anaerobic oxidation of benzene and naphthalene in thermophilic microorganisms from the Guaymas Basin.

Unsubstituted aromatic hydrocarbons (UAHs) are recalcitrant molecules abundant in crude oil, which is accumulated in subsurface reservoirs and occasionally enters the marine environment through natural seepage or human-caused spillage. The challenging anaerobic degradation of UAHs by microorganisms, in particular under thermophilic conditions, is poorly understood. Here, we established benzene- and naphthalene-degrading cultures under sulfate-reducing conditions at 50°C and 70°C from Guaymas Basin sediments. We investigated the microorganisms in the enrichment cultures and their potential for UAH oxidation through short-read metagenome sequencing and analysis. Dependent on the combination of UAH and temperature, different microorganisms became enriched. A Thermoplasmatota archaeon was abundant in the benzene-degrading culture at 50°C, but catabolic pathways remained elusive, because the archaeon lacked most known genes for benzene degradation. Two novel species of Desulfatiglandales bacteria were strongly enriched in the benzene-degrading culture at 70°C and in the naphthalene-degrading culture at 50°C. Both bacteria encode almost complete pathways for UAH degradation and for downstream degradation. They likely activate benzene via methylation, and naphthalene via direct carboxylation, respectively. The two species constitute the first thermophilic UAH degraders of the Desulfatiglandales. In the naphthalene-degrading culture incubated at 70°C, a Dehalococcoidia bacterium became enriched, which encoded a partial pathway for UAH degradation. Comparison of enriched bacteria with related genomes from environmental samples indicated that pathways for benzene degradation are widely distributed, while thermophily and capacity for naphthalene activation are rare. Our study highlights the capacities of uncultured thermophilic microbes for UAH degradation in petroleum reservoirs and in contaminated environments.

Searching for bacteria able to metabolize polycyclic aromatic sulfur compounds in 12-years periodically fed bioreactor.

Biodesulfurization is a promising alternative for removing sulfur molecules from the polycyclic aromatic sulfur compounds (PASC) found in petroleum. PASC consists of recalcitrant molecules that can degrade fuel quality and cause a range of health and environmental problems. Therefore, identifying bacteria capable of degrading PASC is essential for handling these recalcitrant molecules. Microorganisms in environments exposed to petroleum derivatives have evolved specific enzymatic machinery, such as the 4S pathway associated with the dszABC genes, which are directly linked to sulfur removal and utilization as nutrient sources in the biodesulfurization process. In this study, bacteria were isolated from a bioreactor containing landfarm soil that had been periodically fed with petroleum for 12years, using a medium containing dibenzothiophene (DBT), 4.6-dimethylbenzothiophene, 4-methylbenzothiophene, or benzothiophene. This study aimed to identify microorganisms capable of degrading PASC in such environments. Among the 20 colonies isolated from an inoculum containing DBT as the sole sulfur source, only four isolates exhibited amplification of the dszA gene in the dszABC operon. The production of 2-hydroxybiphenyl (HPB) and a decrease in DBT were detected during the growth curve and resting cell assays. The isolates were identified using 16S rRNA sequencing belonging to the genera Stutzerimonas and Pseudomonas. These isolates demonstrated significant potential for biodesulfurization and/or degradation of PASC. All isolates possessed the potential to be utilized in the biotechnological processes of biodesulfurization and degradation of recalcitrant PASC molecules.

Joint Multi-Optimization of an Extremophilic Microbial Bioanode for Mitigation of Mixed Hazardous Azo Dyes in Textile Synthetic Wastewater

Bioelectrochemical systems (BESs), rather than physicochemical processes, are used for wastewater remediation, electricity production, and zero carbon dioxide emission. Textile effluents contain organic and inorganic compounds that can fuel BESs. The main goal of this study was to understand the interplay between the anode material, its surface area, the potential applied to the working electrode (WE), and the concentration of the co-substrate, and how these factors lead to the formation of highly efficient thermohalophilic bioanodes (THB) retrieved from Chott El Djerid (SCD) hypersaline sediment for the treatment of synthetic textile wastewater. To this end, twenty-seven bioanode formation experiments were designed using a Box-Behnken matrix and response surface methodology to understand concomitant interactions. All experiments were conducted in electrochemical reactors of final volume 750 mL inoculated with 80% of enrichment medium containing three azo dyes at a concentration of 300 ppm and 20% of biocatalyst microbial SCD source, at 45 °C. The optimal levels were predicted using NemrodW software as carbon felt (CF) anode material, 6 cm2 anode surface, 7 g/L glucose concentration, and −0.1 V applied potential. These theoretical results were experimentally validated, using maximum current output of 5.23 ± 0.30 A/m2, decolorization rate of 100%, and a chemical oxygen demand (COD) removal rate of 96 ± 1%. Illumina Miseq results revealed that bacterial community harbored the bioanode was dominated at phylum level by Firmicutes (67.1%). At the species level, the biofilm was mainly colonized by Orenia metallireducens species (59.5%). Obtained findings show a promising application of THB in the degradation of recalcitrant molecules as well as for the energy recovery.

Origin of dissolved organic sulfur in marine waters and the impact of abiotic sulfurization on its composition and fate

Despite being the largest reservoir of organic sulfur in the ocean, the major source and reactivity of non-volatile dissolved organic sulfur (DOS) pool in the water column remain uncertain. Three experiments were conducted to fill these gaps. In the first one, sulfur isotopic composition (δ34S) of marine and estuarine organic matter, extracted with various methods, indicated that biotic assimilatory sulfate reduction (ASR) is the main formation pathway of DOS in marine waters and of particulate organic sulfur (POS) in oxic sediment. The abiotic sulfurization by sulfides and polysulfides (e.g., in sulfidic sediment) appeared a negligeable contributor to surface DOS but can nevertheless account for up to 39% of deep oceanic DOS. In contrast, abiotic sulfurization appears to be the dominant source of POS in anoxic sediments. In the two other experiments, the possible contribution of sedimentary porewater DOS to the overlaying water column and the stability of DOS in oxic water, before and after abiotic sulfurization, were assessed. Results indicated that the main sources of water-column and sedimentary DOS are different. Laboratory abiotic sulfurization decreased the stability of the dissolved organic matter (DOM) in oxic conditions but seems to increase the proportion of carboxyl-rich alicyclic molecules (CRAM). In addition, the S/C ratio of the DOM changed during degradation: DOS was immobilized in S-poor non‑sulfurized DOM, but DOS was selectively degraded in S-rich sulfurized DOM. The high degradation rate of porewater DOS could explain why it is not the main contributor to deepwater DOS. Biotic ASR appears as the principal source of both labile and non-labile DOS in marine waters. The preservation of DOS may not be related to sulfur speciation or origin but may be controlled by alterations targeting other elements and leaving behind more recalcitrant molecules containing sulfur atoms.

Decadal application of mineral fertilizers alters the molecular composition and origins of organic matter in particulate and mineral-associated fractions

The extent to which long-term application of mineral fertilizers regulates the quantity, quality, and stability of soil organic matter (SOM) in soil matrices remains unclear. By combining four biomarkers, i.e., free and bound lipids, lignin phenols and amino sugars, we characterized the molecular composition, decomposition and origins of SOM in response to 10-year fertilization (400 kg N ha−1 yr−1, 120 kg P ha−1 yr−1 and 50 kg K ha−1 yr−1) in a cropland in North China. We focused on two contrasting fractions: particulate organic matter (POM), and mineral-associated organic matter (MAOM). Fertilization increased soil organic carbon (SOC) by 23% in MAOM, and altered its composition and origins, despite having a limited effect on bulk SOC levels. Fertilization increased plant-derived terpenoids by 46% in POM and long-chain lipids (≥C20) by 116% in MAOM but decreased short-chain lipids (<C20) by 54% in the former fraction. Fertilization reduced suberin-derived lipids by 56% in POM and 30% in MAOM but increased lignin-derived phenols by 74% in POM and 31% in MAOM, implying that crop residues were preferentially stored via the POM form. Fertilization decreased the contribution of microbial residues to SOC in both the fractions. Overall, mineral fertilizers tended to reduce certain labile components within POM (e.g., short-chain lipids), leading to the accrual of recalcitrant molecules (e.g., long-chain lipids, cutin-derived lipids, and lignin-derived phenols) in the MAOM fraction. Collectively, our study suggests that mineral fertilizers can increase SOM stability and persistence by modifying their molecular composition and preservation in the mineral-organic associations in a temperate agroecosystem.

Electrochemically nanotuned surface comprising 3D bimetallic dendrites fabricated on MWCNT for detection of 1,4-dioxane in water

Water quality has become one of the most serious environmental problems throughout the globe. The recalcitrant molecule, 1,4-Dioxane (1,4-D) has been recognized as a pollutant of rising concern in water, according to the World Health Organization (WHO), and can cause harm to aquatic organisms, animals, and even humans. Thus, it is important to detect 1,4-D in water bodies accurately and sensitively. In light of this, by fine-tuning the electrodeposition conditions, a novel bimetallic copper and gold nanodendritic structure was fabricated on the multiwalled carbon nanotube (MWCNT) functionalized glassy carbon electrode (GCE). The nanosensor was characterized by several physical and electrochemical techniques. The sensor probe exhibits good analytical performance and possess linear dynamic ranges (LDR) between 5 to 103 nM and 0.5 × 105 to 2 × 105 nM. The sensor showed limit of detection (LOD) and limit of quantification (LOQ) of 3.27 ± 0.04 pM and 10.92 ± 0.07 pM, respectively, with a mean response time of 1.65 ± 0.05 s. The sensor's performance was analyzed using tap water and Ganga water, with 90.24–99.57 % and 90.05–98.88 % of 1,4-D recovered without interference, respectively. The entire process of fabricating the surface and testing the 1,4-D takes hardly around 30 min, showing the sensor's applicability in monitoring 1,4-D in the environment.

Land use conversion impacts on the stability of soil organic carbon in Qinghai Lake using 13C NMR and C cycle‐related enzyme activities

AbstractSoil organic carbon (SOC) plays a major role in maintaining long‐term ecological stability. This paper focuses on how land use conversion affects the stability of SOC (e.g., carbon [C] molecular structure) and how soil C cycle‐related enzyme activities are involved in the process. Four land use types around the southern margin of Qinghai Lake were researched: lakeside wetland, natural grassland, cropland, and restored grassland. Soil C was dominated by O‐alkyl carbon (O‐alkyl C, 40.6%–49.3% of total intensity) and alkyl carbon (alkyl C 25.9%–36.7%) in all land use types. Alkyl C and aliphaticity were more abundant in lakeside wetlands than in the other land use types; these values decreased by 29.5% and 36.0%, respectively, after lakeside wetland reclamation. Compared with cropland, restored grassland had higher dissolved organic carbon and β‐glucosidase activity, mainly attributed to the higher plant residues left in the topsoil that provided the polysaccharides required for the higher β‐glucosidase activity. The SOC, labile carbon, alkyl C, and aliphaticity together explained more than 50% of the total variability of soil enzyme activities (p &lt; 0.05) by redundancy analysis, and β‐glucosidase played a regulatory role in soil carbon conversion by path analysis. The lakeside wetland had a more stable SOC than the other land use types around Qinghai Lake at the molecular level due to its higher aliphaticity and aromaticity, which are mainly related to oxygen limitations in lakeside wetlands. To some extent, the accumulation of recalcitrant molecules is limited in restored grassland soils.

Impact of environmental factors on edaphic springtail populations

A description is given of the abiotic and biotic factors that affect edaphic springtail distribution and the main role that collembola play in soil development. Collembola degrade organic matter that has been inoculated with microorganisms, which they control and disperse. They also help decompose recalcitrant molecules in ecosystems, release nitrogen, phosphorus and other elements into soils, and control phytopathogenic fungi in crops, as well as stimulate microbial respiration and serve as soil quality bioindicators. Water is the main factor that determines whether springtail populations are present, followed by temperature, which in turn controls whether new generations will occur. Enzyme metabolism and even DNA structure is affected by pH. Collembola populations are also affected by materials that enter the soil, including the leaf litter dropped by plant coverage, manures and soil fertilizers, and are regulated by the ascending forces in an ecosystem.

Comparing carriers as a support media of white-rot fungi in natural tannins removal

• The growth of white-rot fungi was tested on polyethylene carriers containing cellulose; • Basidiomycetes could cover fully the carriers with the highest cellulose percentage; • B. adusta could grow up to 60% of carrier surface in not-sterile conditions; • B. adusta growth was associated with 25±4% Quebracho tannin sCOD removal; • B. adusta and A. tubingensis could grow together and remove Quebracho sCOD up to 15±4% In the last decades, White-rot Fungi bioremediation potential has been widely investigated, providing remarkable results toward several recalcitrant molecules. However, full-scale applications based on fungi are not employed yet and little is known about their optimal operating conditions, such as i) their ability to grow without sterile conditions, ii) co-substrate requirements and iii) the accurate carrier design for fungal growth. In this study, several batch tests were performed as preliminary steps to evaluate the possible design of a pilot-scale reactor based on fungal biomass to be operated under not-sterile conditions in the removal of Quebracho natural tannin. The tests were performed to verify fungal affinity, including Basidiomycetes and Ascomycetes for innovative cellulose-containing carriers compared to commonly employed PolyUrethane Foam Cubes. In particular, four fungi, including three Basidiomycetes White-rot Fungi, Bjerkandera adusta, Phanerochaete chrysosporium and Tyromyces chioneus and the Ascomycota strain Aspergillus tubingensis , were employed. As a first step, fungi were tested to evaluate their ability to attach and grow onto 12 types of innovative carriers made by High-Density PolyEthylene and containing cellulose in different percentages. Other tests were performed without sterile conditions. In particular, fungal abilities i) to attach and grow onto two different types of support, including cellulose-containing carrier and polyurethane foam cubes and ii) to biotransform recalcitrant molecules (Quebracho natural tannin) iii) to grow and operate synergistically in a consortium of two fungi, were evaluated. The main parameters evaluated were soluble Chemical Oxygen Demand (sCOD) reduction and dry weight increase. Basidiomycetes showed high affinity for cellulose-containing carrierswith the highest cellulose percentage (7%) achieving full colonization and 60% coverage, in sterile conditions and not- sterile conditions, respectively. These results were associated with a Quebracho sCOD removal of 25±4%, without sterility. When combined, the two selected strains, Bjerkandera adusta and Aspergillus tubingensis were able to grow on carriers and to remove up to 15±4% of tannins recalcitrant sCOD. This study provides evidence of i) Basidiomycetes high affinity for cellulose-containing carriers that could favour fungi attachment in sterile and not-sterile conditions, t .and ii) the feasibility of a combined use of Ascomycetes and Basidiomycetes in bioremediation.

Cover Feature: Towards Solving the PFAS Problem: The Potential Role of Metal‐Organic Frameworks (ChemSusChem 19/2022)

The Cover Feature shows an enzyme encapsulated with a metal–organic framework (MOF) degrading a perfluoroalkyl and polyfluoroalkyl substance (PFAS). PFAS are highly recalcitrant molecules that are linked to negative health outcomes. MOFs are tunable and porous materials with ultra-high internal surface areas that can protect proteins from harsh conditions, preventing denaturation. They have also been shown to be effective catalysts, adsorbents, and useful in sensing so have potential in addressing the difficult problem of PFAS decontamination. The protein structure for this image was obtained from RSCB PDB (PDB ID: 1SUV). More information can be found in the Review by L. I. FitzGerald et al.

Removal of Tannic acid and COD from synthetic Tannery wastewater

Tanning industries generate tannery wastewater having high amounts of tannic acid and high COD. Tannery wastewater is difficult to treat as it is having low biodegradability. Tannic acids or tannins are recalcitrant molecules that are toxic to a wide range of microorganisms. In this study, synthetic tannery wastewater treatment was performed by Electrocoagulation (EC) process. To extract the polyphenolic components of tannins, aluminum was employed as an anode electrode and stainless-steel as cathode electrode. Analysis of removal efficiencies was done by determining tannic acid concentration and COD. The effects of functional parameters such as current density, pH, and initial concentration of tannic acid were examined on the efficiency of electrocoagulation. At a current density of 30 A/m2 with an initial concentration of tannic acid of 1,000 mg/L, 94% of tannic acid removal and 94.92% of COD removal were observed. While tannic acid removal was fast, at 60 min, COD removal took a long duration of 120 min. The removal efficiency was observed for three various pH;4.11 (initial pH of the sample), 6, and 8. The maximal COD elimination was found to be accomplished at pH 4.11, which was the sample’s natural pH, whereas tannic acid removal was better at pH 6 and 8. Experiments with a varying initial concentration of tannic acid at 500 mgl−1, 800 mgl−1, and 1000 mgl−1 showed that as concentration was increased, the removal was difficult. The present study found the EC process effective in reducing COD and tannic acid concentration in synthetic tannery wastewater.

Advanced wastewater treatment and membrane fouling control by electro-encapsulated self-forming dynamic membrane bioreactor

An advanced concept of aerobic membrane bioreactors (MBRs) for highly efficient wastewater treatment has been disclosed by introduction of an electro and encapsulated self-forming dynamic biomembrane (e-ESFDM). The biological filtering membrane is intercalated between two woven polyester fabrics as supports that assist the formation and protect the biomembrane. The innovative architecture of the e-ESFDM in combination with electrocoagulation processes resulted in efficient and cost-effective wastewater treatment and control of the membrane fouling. The performance of the e-ESFDMBR was compared to a yet highly efficient ESFDMBR, where the electric field was not present. The ESFDM-based reactors both showed comparable results in the removal of organic matter, in terms of COD and DOC. On the other hand, e-ESFDMBR exceeded the performance of the ESFDMBR in the reduction of nitrogen- and phosphorous-containing pollutants, responsible for eutrophication processes in the environment, and recalcitrant molecules, such as humic-like substances. In addition, an extremely low fouling rate was observed for the e-ESFDM bioreactor. Insights on the biological processes involved in the developed MBR were provided by investigations on the microbiological diversity found in reactor mixed liquor, ESFDM layer and treated wastewater.

Deep ocean microbial communities produce more stable dissolved organic matter through the succession of rare prokaryotes.

The microbial carbon pump (MCP) hypothesis suggests that successive transformation of labile dissolved organic carbon (DOC) by prokaryotes produces refractory DOC (RDOC) and contributes to the long-term stability of the deep ocean DOC reservoir. We tested the MCP by exposing surface water from a deep convective region of the ocean to epipelagic, mesopelagic, and bathypelagic prokaryotic communities and tracked changes in dissolved organic matter concentration, composition, and prokaryotic taxa over time. Prokaryotic taxa from the deep ocean were more efficient at consuming DOC and producing RDOC as evidenced by greater abundance of highly oxygenated molecules and fluorescent components associated with recalcitrant molecules. This first empirical evidence of the MCP in natural waters shows that carbon sequestration is more efficient in deeper waters and suggests that the higher diversity of prokaryotes from the rare biosphere holds a greater metabolic potential in creating these stable dissolved organic compounds.

Microbial and Environmental Processes Shape the Link between Organic Matter Functional Traits and Composition.

Dissolved organic matter (DOM) is a large and complex mixture of molecules that fuels microbial metabolism and regulates biogeochemical cycles. Individual DOM molecules have unique functional traits, but how their assemblages vary deterministically under global change remains poorly understood. Here, we examine DOM and associated bacteria in 300 aquatic microcosms deployed on mountainsides that span contrasting temperatures and nutrient gradients. Based on molecular trait dimensions of reactivity and activity, we partition the DOM composition into labile-active, recalcitrant-active, recalcitrant-inactive, and labile-inactive fractions and quantify the relative influences of deterministic and stochastic processes governing the assembly of each. At both subtropical and subarctic study sites, the assembly of labile or recalcitrant molecules in active fractions is primarily governed by deterministic processes, while stochastic processes are more important for the assembly of molecules within inactive fractions. Surprisingly, the importance of deterministic selection increases with global change gradients for recalcitrant molecules in both active and inactive fractions, and this trend is paralleled by changes in the deterministic assembly of microbial communities and environmental filtering, respectively. Together, our results highlight the shift in focus from potential reactivity to realized activity and indicate that active and inactive fractions of DOM assemblages are structured by contrasting processes, and their recalcitrant components are consistently sensitive to global change. Our study partitions the DOM molecular composition across functional traits and links DOM with microbes via a shared ecological framework of assembly processes. This integrated approach opens new avenues to understand the assembly and turnover of organic carbon in a changing world.

Microbial metabolism changes molecular compositions of riverine dissolved organic matter as regulated by temperature

This study investigated the control of dissolved organic matter (DOM) molecular compositions by microbial community shifts under temperature regulation (range from 5 to 35 °C), using riverine DOM and in situ microorganisms as examples. The functioning of different microbial metabolisms, including the utilization and generation processes, was comprehensively analyzed. Though the overall quantity of DOM was less temperature-affected, more molecules were identified at moderate temperatures (e.g., 15 and 25 °C) and their accumulated mass peak intensities increased with the temperature. The results were ascribed to 1) the microbial production of macromolecular (m/z > 600) CHO, CHON, and CHONS species was stimulated at higher temperatures; 2) the microorganisms consumed more DOM molecules at both higher and lower temperatures; and 3) the simultaneously decreased utilization and increased generation of recalcitrant CHO and CHON molecules with m/z < 600 at higher temperatures. The strong correlations among the temperature, community structures, and DOM chemodiversity suggested that temperature promoted the community evenness to increase the DOM generation. In addition, the higher temperature decreased the abundance of microorganisms that utilized more recalcitrant molecules and produced fewer new molecules (e.g., Proteobacteria, Acinetobacter, and Erythrobacter) while increased others that functioned the opposite (e.g., Verrucomicrobia, Bacteroidetes, and Flavobacterium) to increase the DOM production. The constructed temperature-community-DOM chemistry relationship deepened the molecular-level understanding of DOM variations and provided implications for the warming future.

A fungal symbiont converts provisioned cellulose into edible yield for its leafcutter ant farmers

While ants are dominant consumers in terrestrial habitats, only the leafcutters practice herbivory. Leafcutters do this by provisioning a fungal cultivar (Leucoagaricus gongylophorus) with freshly cut plant fragments and harnessing its metabolic machinery to convert plant mulch into edible fungal tissue (hyphae and swollen hyphal cells called gongylidia). The cultivar is known to degrade cellulose, but whether it assimilates this ubiquitous but recalcitrant molecule into its nutritional reward structures is unknown. We use in vitro experiments with isotopically labelled cellulose to show that fungal cultures from an Atta colombica leafcutter colony convert cellulose-derived carbon into gongylidia, even when potential bacterial symbionts are excluded. A laboratory feeding experiment showed that cellulose assimilation also occurs in vivo in A. colombica colonies. Analyses of publicly available transcriptomic data further identified a complete, constitutively expressed, cellulose-degradation pathway in the fungal cultivar. Confirming leafcutters use cellulose as a food source sheds light on the eco-evolutionary success of these important herbivores.