Organic Carbon Metabolism Research Articles

Fertilization shapes microbial life strategies, carbon and nitrogen metabolic functions in Camellia oleifera soil

Mineral, organic and microbial fertilizers are crucial for maintaining and improving soil quality, ecosystem functions, and fruit yield in Camellia oleifera plantations. However, how the application of these fertilizers shapes the life strategies and functions of soil microbial communities is unclear. Here, we conducted a one-year field experiment with three types of fertilizers: mineral (NPK), manure (Man), and microbial (MicrF), and analyzed soil properties, bacterial and fungal communities to assess microbial life strategies, functional traits and their determinants. The application of MicrF strongly increased the diversity of both soil bacterial (by 6.4%) and fungal communities (by 23%). Organic matter inputs from Man and MicrF had greater effects on the life strategies of bacteria than fungi: the dominant r-strategy bacteria (Proteobacteria, Bacteroidetes, and Actinobacteria) increased with Man and MicrF, but K-strategists (Acidobacteria) decreased. Conversely, the abundance of r-strategy fungi (Ascomycota) decreased, but that of K-fungi (Basidiomycota) increased. Predictions of the functions indicated that microbial fertilization accelerated the bacterial carbohydrates, carbon and nitrogen metabolism, while also increasing the prevalence of wood saprotrophic fungi. The changes in the taxonomic and functional characteristics of the microbial communities induced co-metabolism priming effects, which were mainly regulated by soil organic carbon, available phosphorus, ammonium nitrogen contents, and carbon-nitrogen ratio. The application of MicrF is an effective approach to increase the diversity and multifunctionality of soil microbial communities in Camellia oleifera plantations, including organic matter decomposition, carbon and nitrogen metabolism. These findings provide valuable insights into the fertilizer regimes based on microbial ecological strategies and functional profiles in Camellia oleifera plantations.

Metagenomic analysis reveals abundance of mixotrophic, heterotrophic, and homoacetogenic bacteria in a hydrogen-based membrane biofilm reactor

Heterotrophic microorganisms are frequently observed in hydrogenotrophic denitrification systems and are presumed to contribute to their improved performance. However, their roles and metabolic pathways in the hydrogen-based membrane biofilm reactor (H2−MBfR) system remain unclear. The objective of this study was to elucidate the underlying mechanisms driving heterotrophic denitrification. For this purpose, metagenomic analysis was conducted on an H2−MBfR showing higher denitrification performance, focusing on the metabolic function of the microbial community. Functional genes related to H2 oxidation, organic carbon metabolism, and denitrification were the major targets of interest. This analysis revealed a substantial number of genes associated with the oxidation of organic carbon compounds in the biofilm, suggesting its potential for heterotrophic denitrification. Investigation of the genes of interest in metagenome-assembled genomes (MAGs) has demonstrated a predominance of mixotrophs or heterotrophs rather than obligate autotrophs. Notably, MAGs exhibiting the highest abundance of genes of interest were affiliated with Hydrogenophaga and Thauera, implying their significant role in denitrifying the H2−MBfR as mixotrophs utilizing both H2 and organic substrates. The identification of 11 MAGs, presumed to originate from homoacetogens suggested that acetate might contribute to the proliferation of heterotrophs. Based on these metagenomic findings, possible metabolic pathways were identified to explain heterotrophic denitrification within the H2−MBfR biofilms.

Temperature and Flow Control Organic Carbon Metabolism in Boreal Headwater Streams

AbstractMetabolism in stream ecosystems alters the fate of organic carbon (OC) received from surrounding landscapes, but our understanding of in‐stream metabolic processes in boreal ecosystems remains limited. Determining the factors that regulate OC metabolism will help predict how the C balance of boreal streams may respond to future environmental change. In this study, we addressed the question: what controls OC metabolism in boreal headwater streams draining catchments with discontinuous permafrost? We hypothesized that metabolism is collectively regulated by OC reactivity, phosphorus availability, and temperature, with discharge modulating each of these conditions. We tested these hypotheses using a combination of laboratory experiments and whole‐stream ecosystem metabolism measurements throughout the Caribou‐Poker Creeks Research Watershed (CPCRW) in Interior Alaska, USA. In the laboratory experiments, respiration and dissolved OC (DOC) removal were both co‐limited by the supply of reactive C and phosphorus, but temperature and residence time acted as stronger controls of DOC removal. Ecosystem respiration (ER) was largely predicted by discharge and site, with some variance explained by gross primary production (GPP) and temperature. Both ER and GPP varied inversely with watershed permafrost extent, with an inverse relationship between temperature and permafrost extent providing one plausible explanation. Our results provide some of the first evidence of a functional response to permafrost thaw in stream ecosystems and suggest the role of metabolism in landscape C cycling may increase as climate change progresses.

Stable isotope labeling and functional gene prediction elucidate the carbon metabolism in fermentative bacteria and microalgae coupling system

The application of the fermentative bacteria and microalgae coupling system in the wastewater treatment has been studied, but there remains few knowledge regarding the organic and inorganic carbon metabolism within this system. In this study, the carbon metabolism of microalgae and fermentative bacteria was elucidated by 13C stable isotope labeling and functional gene prediction, respectively. The 13C glucose and 13C NaHCO3 were used as stable isotope tracers to clarify the organic and inorganic carbon metabolism of microalgae, indicating that approximately 71.5 % of the Acetyl-CoA in microalgae was synthesized from organic carbon sources, while 26.8 % was synthesized through the utilization of inorganic carbon sources. Inorganic carbon sources can enhance the activity of photosynthetic system and facilitate the Calvin cycle. Considering the adequate organic carbon sources and insufficient inorganic carbon sources in the fermentative bacteria and microalgae coupling system, NaHCO3 was added to improve carbon utilization of microalgae. The maximum microalgal lipid yield reached 1130.37 mg/L with 1000 mg/L NaHCO3 supplementation. Functional gene prediction was used to analysis the effect of various carbon composition on the bacterial carbon metabolism. Notably, the additional inorganic carbon sources increased the abundance of bacterial functional genes associated with the fermentation and acetic acids synthesis, which was advantageous for VFAs production and further promoted microalgae growth. This study can gain a deeper understanding of microbial metabolic mechanisms during the operation of fermentative bacteria and microalgae system, and improve its sustained operational stability.

Community Composition and Functional Characterization of Microorganisms in Surface Sediment of the New Britain Trench.

The deep-sea harbors abundant prokaryotic biomass is a major site of organic carbon remineralization and long-term carbon burial in the ocean. Deep-sea trenches are the deepest part of the ocean, and their special geological and morphological features promoting the accumulation of organic matter and active organic carbon turnover. Despite the expanding reports about the organic matter inputs, limited information is known regarding microbial processes in deep-sea trenches. In this study, we investigated the species composition and metabolic potential in surface sediment of the New Britain Trench (NBT), using a metagenomic approach. The predominant microbial taxa in NBT sediment include Proteobacteria, Acidobacteria, Planctomycetes, Actinobacteria and Chloroflexota. The microbial communities showed highly diverse metabolic potentials. Particularly, genes encoding enzymes for degradation of aromatic compounds, as well as those encoding haloalkane dehalogenase and haloacetate dehalogenase were annotated in the NBT surface sediment, which indicate the potential of microorganisms to degrade different types of refractory organic matter. The functional genes encoding enzymes for dissimilatory nitrate reduction, denitrification, and nitrification were also represented in the NBT metagenome. Overall, the microbial communities show high diversity of heterotrophic lineages and metabolic features, supporting their potential contributions in organic carbon metabolism. Meanwhile, Nitrosopumilus, a dominant genus in the surface sediment of the NBT, is a typical ammonia-oxidizing archaea (AOA), with autotrophic CO2 fixation pathways including the 3-hydroxypropionate/4-hydroxybutylate (3HP/4HB) cycle, the reductive TCA (rTCA) cycle. The results demonstrate that autotrophic metabolic processes also play an important role in the surface sediment, by providing newly synthesized organic matter.

Iron-carbon microelectrolysis coordinated advanced N and P removal from municipal tailwater: Unexpected N conversion and microbial characteristic

The biochemical mechanisms that iron-carbon microelectrolysis (IC-ME) advanced and coordinated treating nitrogen (N) and phosphorus (P) from tailwater are not intensive. Depending on the optimal operating conditions of the iron carbon biofilter (ICBF), the interface P reaction, functional microbial community and characteristics were analyzed. Results demonstrated that iron (Fe) engaged in reaction with nitrate nitrogen (NO3−-N), facilitating the release of both nitrite nitrogen (NO2−-N) and ammonia nitrogen (NH4+-N) to 0.75 and 2.46 mg/L. Total nitrogen (TN) and total phosphorus (TP) were simultaneously removed lower than 10 and 0.3 mg/L under the optimum conditions i.e., gas water ratio of 15, empty bed contact time (EBCT) of 105 min, and backwashing cycle of 12 h. Microelectrolysis (ME) exhibited a robust capacity to degrade macromolecular pollutants, and P was predominantly eliminated via Fe3(PO4)2 and Fe4(PO4)3(OH)2 precipitation. Intriguingly, IC-ME did alter the microbial community composition, especially the Fe-containing microflora (Desulfuromonas, Azospira, Denitratisoma, Rhodobacter and Paludibaculum). The relatively high abundance of Gammaproteobacteria (29.67–38.3 %) promoted N transformation and the N cycle was mainly dominated by nitrogen respiration (1.95–3.39 %), nitrate reduction (2.06–3.45 %) and nitrate respiration (1.95–3.39 %). ME invigorated functional metabolism, thereby promoting organic carbon metabolism.

Carbon starvation raises capacities in bacterial antibiotic resistance and viral auxiliary carbon metabolism in soils

Organic carbon availability in soil is crucial for shaping microbial communities, yet, uncertainties persist concerning microbial adaptations to carbon levels and the ensuing ecological and evolutionary consequences. We investigated organic carbon metabolism, antibiotic resistance, and virus-host interactions in soils subjected to 40 y of chemical and organic fertilization that led to contrasting carbon availability: carbon-poor and carbon-rich soils, respectively. Carbon-poor soils drove the enrichment of putative genes involved in organic matter decomposition and exhibited specialization in utilizing complex organic compounds, reflecting scramble competition. This specialization confers a competitive advantage of microbial communities in carbon-poor soils but reduces their buffering capacity in terms of organic carbon metabolisms, making them more vulnerable to environmental fluctuations. Additionally, in carbon-poor soils, viral auxiliary metabolic genes linked to organic carbon metabolism increased host competitiveness and environmental adaptability through a strategy akin to "piggyback the winner." Furthermore, putative antibiotic resistance genes, particularly in low-abundance drug categories, were enriched in carbon-poor soils as an evolutionary consequence of chemical warfare (i.e., interference competition). This raises concerns about the potential dissemination of antibiotic resistance from conventional agriculture that relies on chemical-only fertilization. Consequently, carbon starvation resulting from long-term chemical-only fertilization increases microbial adaptations to competition, underscoring the importance of implementing sustainable agricultural practices to mitigate the emergence and spread of antimicrobial resistance and to increase soil carbon storage.

Response of Organic Carbon Mineralization to Nitrogen Addition in Micro-aerobic and Anaerobic Layers of Paddy Soil

In field conditions, a micro-aerobic layer with 1 cm thickness exists on the surface layer of paddy soil owing to the diffusion of dissolved oxygen via flooding water. However, the particularity of carbon and nitrogen transformation in this specific soil layer is not clear. A typical subtropical paddy soil was collected and incubated with13C-labelled rice straw for 100 days. The responses of exogenous fresh organic carbon(13C-rice straw) and original soil organic carbon mineralization to nitrogen fertilizer addition[(NH4)2SO4]in the micro-aerobic layer(0-1 cm) and anaerobic layer(1-5 cm) of paddy soil and their microbial processes were analyzed based on the analysis of 13C incorporation into phospholipid fatty acid(13C-PLFAs). Nitrogen addition promoted the total CO2 and 13C-CO2 emission from paddy soil by 11.4% and 12.3%, respectively. At the end of incubation, with the addition of nitrogen, the total soil organic carbon (SOC) and13C-recovery rate from rice straw in the anaerobic layer were 2.4% and 9.2% lower than those in the corresponding micro-aerobic layer, respectively. At the early stage(5 days), nitrogen addition increased the total microbial PLFAs in the anaerobic layer with a consistent response of bacterial and fungal PLFAs. However, there was no significant effect from nitrogen on microbial abundance in the micro-aerobic layer. Nitrogen addition had no significant impact on the abundance of total 13C-PLFAs in the micro-aerobic and anaerobic layers, but the abundance of 13C-PLFAs for bacteria and fungi in the micro-aerobic layer was decreased dramatically. At the late stage(100 days), the effect of nitrogen addition on microbial PLFAs was consistent with that at the early stage. The abundances of total, bacterial, and fungal 13C-PLFAs were remarkably increased in the anaerobic layer. However, the abundance of 13C-PLFAs in the micro-aerobic layer showed no significant response to nitrogen addition. During the incubation, the content of NH4+-N in the anaerobic soil layer was higher than that in the micro-aerobic soil layer. This indicates that nitrogen addition increased microbial activity in the anaerobic soil layer caused by the higher NH4+-N concentration, as majority of microorganisms preferred to use NH4+-N. Consequently, the microbial utilization and decomposition of organic carbon in the anaerobic soil layer were accelerated. By contrast, richer available N existed in the form of NO3--N in the micro-aerobic soil layer owing to the ammoxidation process. Thus, the shortage of NO3--N preference microorganisms in the paddy soil environment prohibited the microbial metabolism of organic carbon in the micro-aerobic layer. As a whole, nitrogen fertilization enhanced organic carbon loss via microbial mineralization in paddy soil with a weaker effect in the micro-aerobic layer than that in the anaerobic layer, indicating the limited microbial metabolic activity in the surface micro-aerobic layer could protect the organic carbon stabilization in paddy soil. This study emphasizes the heterogeneity of paddy soil and its significant particularity of carbon and nitrogen transformation in micro-aerobic layers. Consequently, this study has implications for optimizing the forms and method for the application of nitrogen fertilizer in paddy cropping systems.

Daily variability of pH and temperature in seawater from a near-pristine oceanic atoll, Southwest Atlantic

The study of pH and temperature variability in reef environments, and the underlying processes that control this variability, is of great importance for ocean acidification research. Therefore, in the reef environment of Rocas Atoll, we conducted continuous monitoring of pH and temperature and periodic sampling of carbonate chemistry, and we hypothesize that seawater temperature is not the determining factor in the daily variability of pH at this atoll. Our results showed that the seawater of the atoll presented a high daily variability in pH, [H+], and temperature. The cycles of variations occurred primarily with a periodicity of ∼24 h, related to the daily light cycle, and secondarily with a periodicity of ∼12 h, associated with the semi-diurnal tidal cycles of the atoll. The results indicate that the relative balance of net organic carbon metabolism is the main process modulating carbonate chemistry on the atoll throughout the day.

Effects of the polyhalogenated carbazoles 3-bromocarbazole and 1,3,6,8-tetrabromocarbazole on soil microbial communities

Soil ecosystems are being more contaminated with polyhalogenated carbazoles (PHCZs), which raising much attention about their impact on soil microorganisms. 3-Bromocarbazole (3-BCZ) and 1,3,6,8-tetrabromocarbazole (1,3,6,8-TBCZ) are two typical PHCZs with high detection rates in the soil environment. However, ecological risk research on these two PHCZs in soil is still lacking. In the present study, after 80 days of exposure, the ecological influence of 3-BCZ and 1,3,6,8-TBCZ was investigated based on 16S rDNA sequencing, ITS sequencing, gene (16S rDNA, ITS, amoA, nifH, narG and cbbL) abundance and soil enzyme activity. The results showed that the bacterial 16S rDNA gene abundance significantly decreased under 3-BCZ and 1,3,6,8-TBCZ exposure after 80 days of incubation. The fungal ITS gene abundance significantly decreased under 1,3,6,8-TBCZ (10 mg/kg) exposure. PHCZs contributed to the alteration of bacteria and fungi community abundance. Bacteria Sphingomonas, RB41 and fungus Mortierella, Cercophora were identified as the most dominant genera. The two PHCZs consistently decreased the relative abundance of Sphingomonas, Lysobacter, Dokdonella, Mortierella and Cercophora etc at 80th day. These keystone taxa are related to the degradation of organic compounds, carbon metabolism, and nitrogen metabolism and may thus have influence on soil ecological functions. Bacterial and fungal functions were estimated using functional annotation of prokaryotic taxa (FAPROTAX) and fungi functional guild (FUNGuild), respectively. The nitrogen and carbon metabolism pathway were affected by 3-BCZ and 1,3,6,8-TBCZ. The soil nitrogen-related functions of aerobic ammonia oxidation were decreased but the soil carbon-related functions of methanol oxidation, fermentation, and hydrocarbon degradation were increased at 80th day. The effects of 3-BCZ and 1,3,6,8-TBCZ on the abundances of the amoA, nifH, narG, and cbbL genes showed a negative trend. These results elucidate the ecological effects of PHCZs and extend our knowledge on the structure and function of soil microorganisms in PHCZ-contaminated ecosystems.

Efficient nitrogen removal from municipal wastewater by an autotrophic-heterotrophic coupled anammox system: The up-regulation of key functional genes

The metabolic pathways based on key functional genes were innovatively revealed in the autotrophic-heterotrophic coupled anammox system for real municipal wastewater treatment. The nitrogen removal performance of the system was stabilized at 88.40 ± 3.39 % during the treatment of real municipal wastewater. The relative abundances of the nitrification functional genes ammonia oxidase (amoA/B/C), hydroxylamine oxidoreductase (hao), and nitrite oxidoreductases (nxrA/B) were increased by 1.2–2.4 times, and these three nitrification functional genes were mostly contributed by Nitrospira that dominated the efficient nitrification of the system. The relative abundance of anammox bacteria Candidatus Brocadia augmented from 0.35 % to 0.75 %, accompanied with the increased expression of hydrazine synthase (hzs) and hydrazine dehydrogenase (hdh), resulting in the major role of anammox (81.24 %) for nitrogen removal. The expression enhancement of the functional genes nitrite reductase (narG/H, napA/B) that promoted partial denitrification (PD) of the system weakened the adverse effects of the sharp decline in the population of PD microbe Thauera (from 5.7 % to 2.2 %). The metabolic module analysis indicated that the carbon metabolism pathways of the system mainly included CO2 fixation and organic carbon metabolism, and the stable enrichment of autotrophic bacteria ensured stable CO2 fixation. Furthermore, the enhanced expression of the glucokinases (glk, GCK, HK, ppgk) and the abundant pyruvate kinase (PK) achieved stable hydrolysis ability of organic carbon metabolism function of the system. This study offers research basics to practical application of the mainstream anammox process.

Effects of soil organic carbon metabolism on electro-bioremediation of petroleum-contaminated soil

Soil organic carbon (SOC) potentially interacts with microbial metabolism and may affect the degradation of petroleum-derived carbon (PDC) in the electro-bioremediation of petroleum-contaminated soil. This study evaluated the interactions among organic carbon, soil properties, and microbial communities to explore the role of SOC during the electro-bioremediation process. The results showed that petroleum degradation exerted superposition and synergistic electrokinetic and bioremediation effects, as exemplified by the EB and EB-PR tests, owing to the maintenance and enhancement of SOC utilization (P/S value), respectively. The highest P/S value (2.0–2.4) was found in the electrochemical oxidation zone due to low SOC consumption. In the biological oxidation zones, electric stimulation enhanced the degradation of PDC and SOC, with higher average P/S values than those of the Bio test. Soil pH, Eh, inorganic ions, and bioavailable petroleum fractions were the main factors reshaping the microbial communities. SOC metabolism effectively buffered the stress of environmental factors and pollutants while maintaining functional bacterial abundance, microbial alpha diversity, and community similarity, thus saving the weakened PDC biodegradation efficiency in the EB and EB-PR tests. The study of the effect of SOC metabolism on petroleum biodegradation contributes to the development of sustainable low-carbon electro-bioremediation technology.

Enhanced Regional Variability of Seawater pCO2 Under Human and Natural Interference in a Nearshore Coral Nature Reserve (Dongshan Island, China)

AbstractCO2 signatures differ among locations, even within the same coastal habitat. However, the driving mechanism behind this variation is not well understood due to the presence of both human and natural stresses. This study examines seawater pCO2 and its deviation from the regional average (defined as pCO2 anomaly) during spring, summer, and winter at two contrasting zones (trial and core zones) of Dongshan coral habitat. The impact of solar, tidal, and biological cycles on pCO2 anomaly is relatively small under the designed sampling scheme. Results show that there is a large positive pCO2 anomaly in the turbid water of the trial zone during all studied seasons, while the large negative pCO2 anomaly in the core zone only occurs during the summer upwelling season. This indicates that CO2 signatures among locations may have seasonality. The physical and biological contributors to pCO2 anomaly are then quantitatively revealed based on a first‐order Taylor decomposition and biological carbon metabolisms. The results suggest that organic carbon metabolism of marine phytoplankton dominated pCO2 anomaly in all three seasons, while inorganic carbon metabolism also enlarged pCO2 anomaly, especially during summer. Physical contributions were minor. Moreover, significant linear correlations between turbidity (related to local human activities), chlorophyll (related to coastal upwelling) and changes in dissolved inorganic carbon (induced by organic carbon metabolism) indicate human and natural influences on bioprocesses, which may enhance pCO2 anomaly. Finally, the Dongshan coral habitat was estimated as a source of atmospheric CO2, with an annual efflux of approximately 50 t C.

Evaluation of sludge anaerobic fermentation driving partial denitrification capability: In view of kinetics and metagenomic mechanisms

Partial denitrification (PD) provides a promising approach of efficient and stable nitrite (NO2−-N) generation for annamox. In this study, the feasibility of short-term sludge anaerobic fermentation driving PD was evaluated. It was found that a higher NO2−-N accumulation in nitrate (NO3−-N) reduction was obtained with the 5-days fermented sludge compared to 8 and 15-days fermentation. Moreover, compared to acetate as carbon source, sludge fermentation products (SFPs) induced the higher NO2−-N production with nitrate-to-nitrite transformation ratio (NTR) nearly 100 %. Denitrification activity of fermented sludge were obviously improved with SFPs as electron donor. Metagenomic analysis revealed that Thauera was the dominant bacteria, which was assumed to be the key contributor to PD performance by harboring the highest narGHI and napAB but much lower nirS and nirK. Under the conditions of SFPs and fermented sludge, Thauera was speculated to have higher resistance than other denitrifiers attributed to versatile carbon metabolic capabilities utilizing SFPs with the significantly improved genes for metabolism of complex organic carbon via glycolysis after anaerobic fermentation. A novel integration of sludge fermentation driving PD and anammox for mainstream wastewater treatment and sidestream polishing was proposed to offer a promising application with reduced commercial carbon source consumption and waste sludge reduction.

Dynamics of O2 and pCO2 in a Southeast Asia seagrass meadow: Metabolic rates and carbon sink capacity

Dissolved oxygen (DO) and partial pressure of CO2 (pCO2) were measured at half-hourly intervals from June 29 to September 9, 2019, in a seagrass meadow in the Southeast Asia archipelagos region. The open water mass balance of the O2 approach was used to calculate metabolic rates (i.e., gross primary production (GPP), community respiration (CR), and net community production (NCP). The calculations show that GPP and CR rates in the seagrass meadow of Dongsha Island were approximately 2.5 times higher than the global means (GPP, 507 ± 173 vs. 225 ± 11 mmol O2 m-2 d-1; CR, 497 ± 171 vs. 188 ± 10 mmol O2 m-2 d-1), while NCP was similar to the global mean (8 ± 61 vs. 27 ± 6 mmol O2 m-2 d-1), suggesting that seagrass meadows with high GPP may not necessarily hold high potential for carbon sequestration. The current data set also reveal that NCP tended to increase with GPP only at lower GPP levels, while NCP did not increase with GPP anymore at higher GPP levels. Moreover, the autotrophic/heterotrophic status did not correspond well to the sink/source behavior of CO2, suggesting that organic carbon metabolism could not be the only dominant factor in determining the sink/source status in a typical seagrass meadow underlain by carbonate sediments, which was further supported by the observed decrease in the trend of pCO2 with a relatively stable NCP level over the study period. These results demonstrate that the metabolism and the relationship between NCP and pCO2 in the seagrass meadows of Dongsha Island may deviate greatly from the global mean condition. To obtain a better assessment of the global potential of seagrass meadows as a nature-based solution for carbon sequestration, more regional-specific studies are still needed in the key regions, such as Indonesia and the Pacific archipelagos, that support extensive seagrass meadows but have not been charted.

Biofilm characteristics for providing resilient denitrification in a hydrogen-based membrane biofilm reactor

In a hydrogen-based membrane biofilm reactor (H2-MBfR), the biofilm thickness is considered to be one of the most important factors for denitrification. Thick biofilms in MBfRs are known for low removal fluxes owing to their resistance to substrate transport. In this study, the H2-MBfR was operated under various loading rates of oxyanions, such as NO3-N, SO4-S, and ClO4− at an H2 flux of 1.06 e− eq/m2-d. The experiment was initiated with NO3-N, SO4-S, and ClO4− loadings of 0.464, 0.026, and 0.211 e− eq/m2-d, respectively, at 20 °C. Under the most stressful conditions, the loading rates increased simultaneously to 1.911, 0.869, and 0.108 e− eq/m2-d, respectively, at 10 °C. We observed improved performance in significantly thicker biofilms (approximately 2.7 cm) compared to previous studies using a denitrifying H2-MBfR for 120 days. Shock oxyanion loadings led to a decrease in total nitrogen (TN) removal by 20 to 30%, but TN removal returned to 100% within a few days. Similarly, complete denitrification was observed, even at 10 °C. The protective function and microbial diversity of the thick biofilm may allow stable denitrification despite stress-imposing conditions. In the microbial community analysis, heterotrophs were dominant and acetogens accounted for 11% of the biofilm. Metagenomic results showed a high abundance of functional genes involved in organic carbon metabolism and homoacetogenesis. Owing to the presence of organic compounds produced by acetogens and autotrophs, heterotrophic denitrification may occur simultaneously with autotrophic denitrification. As a result, the total removal flux of oxyanions (1.84 e− eq/m2-d) far exceeded the H2 flux (1.06 e− eq/m2-d). Thus, the large accumulation of biofilms could contribute to good resilience and enhanced removal fluxes.

Degradable intracellular self-functionalized nanoprobes for in vitro diagnosis and monitoring of cancer

Despite various attempts to accelerate nanoparticle clearance from the cell, considerable amounts of nanomaterials remain in the cell, impairing cellular activities and hence precluding reliable invitro diagnosis. Retention of nanoparticles in cellular organelles disturbs cellular equilibrium and induces long-term consequences such as change in cell phenotype, genotype, cell mobility, toxicity, and even cell death. As a result, it is necessary to produce nanoparticles that degrade promptly and are then safely expelled from the cell while remaining biocompatible and fully functional. Here, we present a metabolizable organic carbon probe functionalized for Raman and fluorescence that can be used to track and monitor metabolizable organic carbon probe breakdown in lysosomes while simultaneously performing molecular level probing for invitro cancer diagnosis. The probes were stable in medium and other fluids and degraded in cancer cells within a week. The probes demonstrated an excellent Raman signal, which allowed surface-enhanced Raman spectroscopy-based monitoring of the degradation. Additionally, the probes showed the property of fluorescence which can be attributed to the inherent fluorescence of the probe on quantum scale. Experimental evidence of self-metabolization of the probe was further demonstrated. We tested the ability of the probes for cancer diagnosis with two cancer cell lines (breast and lung) and experimentally demonstrated the ability to discriminate between breast cancer and lung cancer without any ambiguity. These findings establish a novel type of functionalized degradable nanostructure for intracellular sensing and imaging cancer cells in cellular nanomedicine.

Organic carbon metabolism is a main determinant of hydrogen demand and dynamics in anaerobic soils.

Hydrogen (H2) is a crucial electron donor for many processes in the environment including nitrate-, sulfate- and, iron-reduction, homoacetogenesis, and methanogenesis, and is a major determinant of microbial competition and metabolic pathways in groundwater, sediments, and soils. Despite the importance of H2 for many microbial processes in the environment, the total H2 consuming capacity (or H2 demand) of soils is generally unknown. Using soil microcosms with added H2, the aims of this study were 1) to measure the H2 demand of geochemically diverse soils and 2) to define the processes leading to this demand. Study results documented a large range of H2 demand in soil (0.034-1.2 millielectron equivalents H2 g-1 soil). The measured H2 demand greatly exceeded the theoretical demand predicted based on measured concentrations of common electron acceptors initially present in a library of 15 soils. While methanogenesis accounted for the largest fraction of H2 demand, humic acid reduction and acetogenesis were also significant contributing H2-consuming processes. Much of the H2 demand could be attributed to CO2 produced during incubation from fermentation and/or acetoclastic methanogenesis. The soil initial total organic carbon showed the strongest correlation to H2 demand. Besides external additions, H2 was likely generated or cycled in the microcosms. Apart from fermentative H2 production, carboxylate elongation to produce C4-C7 fatty acids may have accounted for additional H2 production in these soils. Many of these processes, especially the organic carbon contribution is underestimated in microbial models for H2 consumption in natural soil ecosystems or during bioremediation of contaminants in soils.

Effects of Exogenous Glucose on Soil Organic Carbon Sequestration and Carbon Metabolism in Root of Malus baccata (L.) Bork

ABSTRACT Labile carbon (C) inputs to soil affect organic C dynamics in soil and the pathway of energy metabolism in tissue of plants. However, studies focusing on orchard soil are still scarce. In this study, the fate of 13C-glucose in organic C components, and the C metabolism in root of Malus baccata (L.) Borkh. in response to exogenous glucose at two levels, 1.50 g kg−1 (GLC1) and 7.50 g kg−1 (GLC2), were evaluated. Glucose addition increased the δ13C values and contents of soil organic carbon (SOC) and active fractions including microbial biomass carbon (MBC), dissolved organic carbon (DOC) pools, and particulate organic carbon (POC). At the end of the experiment, the MBC, DOC, and POC contents in GLC1 were 3.20%, 14.26%, and 5.16% higher than those in GLC2, respectively. In addition, no marked difference was found for SOC content between these two glucose rates. At the end of incubation, glucose-C was mostly allocated to SOC (56.79–85.05%), followed by DOC (4.72–20.88%) and MBC (4.46–18.1%); the lowest percentage was in POC (3.86–5.77%). Exogenous glucose increased the contents of organic acids and activities of key enzymes related with C metabolism in roots of M. baccata. In addition, adenosine triphosphate content, the energy matter, in root under GLC1 was 22.35% higher than that under GLC2. Correlation analyses suggested that the soil organic C fractions were positively correlated with C metabolism parameters in the roots of M. baccata. Overall, glucose addition improved the C metabolism in roots and the allocation of glucose-derived C in soil.

A growth-boosting synergistic mechanism of Chromochloris zofingiensis under mixotrophy

The mixotrophic cultivation approach, consisting of heterotrophy and photoautotrophy, has been suggested as a promising strategy to reach a high growth rate and biomass productivity. However, the underlying growth-boosting mechanisms remain elusive. In this study, Chromochloris zofingiensis, a promising high-value-added astaxanthin producer, was selected to elucidate how mixotrophy benefits cellular growth. Results showed that mixotrophy yielded the highest biomass, which was significantly higher than the sum of photoautotrophic and heterotrophic cultivation, indicating a significant growth-boosting effect. The chlorophyll fluorescence and transcriptomics results confirmed that the highest biomass production under mixotrophy was attributed to a higher photosynthesis performance, decreased light damage and photorespiration, as well as significantly upregulated glucose metabolism compared to photoautotrophy. Compared to heterotrophy, mixotrophy consumed less glucose and had a lower glucose metabolic efficiency, but led to higher biomass yield. Taken together, we propose a synergistic growth-promoting mechanism between photosynthesis and glucose metabolism under mixotrophy, in which cells not only directly benefit from extra energy from exogenous organic carbon metabolism but also the reutilization of the byproduct CO2 for photosynthesis. In return, O2 evolved from photosynthesis was consumed by glucose metabolism as well. Furthermore, the coexistence of photosynthesis and glucose metabolism contributes to higher energy usage efficiency and biomass yield, correspondingly diminishing the waste and decreasing the damage. This study provides insights into the synergistic mechanism under mixotrophy and helps to better select growth strategies for commercially valuable algal species.