Anaerobic Utilization Research Articles

Comparison study on silicon forms and leaching characteristics of pyrolysis biochar and hydrochar derived from cow dung digestate

Silicon in soil is critical for crop growth and tolerance to both biotic and abiotic stresses. Si-rich biochar can be used as soil supplements for silicon improvement. In order to investigate the application potential of silicon in pyrolysis biochar (PC) and hydrochar (HC) derived from cow dung digestate (CD), they were compared at different temperatures to explore silicon forms and leaching characteristics. The results indicated that the form and content of silicon changed obviously with variations in pyrolysis temperature. The form of silicon content followed the order of amorphous silicon ≫ available silicon > active silicon > dissolved silicon in PC. For HC, the form of silicon content followed the order of amorphous silicon ≫ dissolved silicon > active silicon > available silicon. Compared to HC, PC had a richer pore-layered structure but fewer surface functional groups. The study of dissolving kinetics of silicon indicated that PC550 released the most silicon, which was 3 times more than HC220. The long-term silicon leaching found that PC550 increased rapidly with reaction time, whose dissolving silicon increased to 33.02 mg/g, which was much higher than the recommended silicon content of soil in China (0.095 mg/g soil). This study offers a novel point of view for anaerobic digestion residue utilization as a fertilizer.

Eco-environmental responses of Eichhornia crassipes rhizobacteria community to co-stress of per(poly)fluoroalkyl substances and microplastics

The stabilization of rhizobacteria communities plays a crucial role in sustaining healthy macrophyte growth. In light of increasing evidence of combined pollution from microplastics (MPs) and per- and polyfluoroalkyl substances (PFASs), Selecting typical floating macrophyte as a case, this study explored their impacts using hydroponic simulations and 16S rRNA high-throughput sequencing. A total of 31 phyla, 77 classes, 172 orders, 237 families, 332 genera, and 125 rhizobacteria species were identified. Proteobacteria (16.19% to 57.70%) was the dominant phylum, followed by Bacteroidota (12.34% to 44.48%) and Firmicutes (11.31% to 36.36%). In terms of α-diversity, polystyrene (PS) MPs and PFASs significantly impacted community abundance (ACE and PD-tree) rather than evenness (Shannon and Pielou) compared to the control. βMNTD and βNTI analyses revealed that PS MPs enhanced deterministic assembly processes driven by F-53B and GenX, while mitigating those induced by PFOA and PFOS. Contamination treatments narrowed the ecological niche breadths at both the phylum (5% (PS) to 49.91% (PS & PFOA)) and genus levels (8% (PS) to 63.96% (PS & PFOA)). Functionally, MPs and PFASs decreased the anaerobic capacity and ammonia nitrogen utilization of rhizosphere bacteria. This study enhances our understanding of the microecological responses of macrophyte-associated bacteria to combined MP and PFAS contamination and offers insights into ecological restoration strategies and mitigating associated environmental risks.

The biotechnological potential of the Chloroflexota phylum.

In the next decades, the increasing material and energetic demand to support population growth and higher standards of living will amplify the current pressures on ecosystems and will call for greater investments in infrastructures and modern technologies. A valid approach to overcome such future challenges is the employment of sustainable bio-based technologies that explore the metabolic richness of microorganisms. Collectively, the metabolic capabilities of Chloroflexota, spanning aerobic and anaerobic conditions, thermophilic adaptability, anoxygenic photosynthesis, and utilization of toxic compounds as electron acceptors, underscore the phylum's resilience and ecological significance. These diverse metabolic strategies, driven by the interplay between temperature, oxygen availability, and energy metabolism, exemplify the complex adaptations that enabled Chloroflexota to colonize a wide range of ecological niches. In demonstrating the metabolic richness of the Chloroflexota phylum, specific members exemplify the diverse capabilities of these microorganisms: Chloroflexus aurantiacus showcases adaptability through its thermophilic and phototrophic growth, whereas members of the Anaerolineae class are known for their role in the degradation of complex organic compounds, contributing significantly to the carbon cycle in anaerobic environments, highlighting the phylum's potential for biotechnological exploitation in varying environmental conditions. In this context, the metabolic diversity of Chloroflexota must be considered a promising asset for a large range of applications. Currently, this bacterial phylum is organized into eight classes possessing different metabolic strategies to survive and thrive in a wide variety of extreme environments. This review correlates the ecological role of Chloroflexota in such environments with the potential application of their metabolisms in biotechnological approaches.

Attempts of B-site doped LaFeO3 oxygen carriers in high-moisture content biomass chemical looping gasification

With the rapid development of anaerobic digestion engineering, the disposal and utilization of digestate are urgently required. Chemical looping gasification (CLG) technology provides potential for eliminate digestate and convert it into high-quality syngas. However, the application of conventional CLG is hindered by the high-moisture content of digestate. In order to decrease the energy consumption of dehydration, this work aims to optimize the CLG process by developing new oxygen carrier (OC) to enhance the transition of self-moisture of digestate. LaFeO3 was employed as the basic OC and Cr, Co, Cu were further doped on the B-site to form LaB0.5Fe0.5O3 (B = Cr, Co, Cu). H2O-TPD, OH/FTIR, NH3-Drifts, Raman, and XPS were employed to analyze the adsorption and dissociation of H2O by different OCs. Results indicated that LaFeO3 and LaB0.5Fe0.5O3 exhibited a synergistic effect with H2O, enabling adsorption of H2O at low temperatures and dissociation at high temperatures. In this case, it allows OC to capture H2O in the initial drying stage, then release H2O and OH at higher temperatures to participate in subsequent reactions, thus significantly increase the gasification performance. Fixed-bed CLG experiments were conducted to corroborate the characterization results. LaCu0.5Fe0.5O3 showcased the best gasification effect, achieving 81.83 % efficiency at a digestate moisture content of 40 %, surpassing LaFeO3 CLG by 5 %. Moreover, LaCu0.5Fe0.5O3 exhibited a noticeable catalytic effect and lowered the activation energy (E). Kinetic analysis revealed a 16 % reduction in E for LaCu0.5Fe0.5O3 CLG in comparison to LaFeO3 CLG.

Noninvasive assessment of metabolic turnover during inflammation by in vivo deuterium magnetic resonance spectroscopy.

Inflammation and metabolism exhibit a complex interplay, where inflammation influences metabolic pathways, and in turn, metabolism shapes the quality of immune responses. Here, glucose turnover is of special interest, as proinflammatory immune cells mainly utilize glycolysis to meet their energy needs. Noninvasive approaches to monitor both processes would help elucidate this interwoven relationship to identify new therapeutic targets and diagnostic opportunities. For induction of defined inflammatory hotspots, LPS-doped Matrigel plugs were implanted into the neck of C57BL/6J mice. Subsequently, 1H/19F magnetic resonance imaging (MRI) was used to track the recruitment of 19F-loaded immune cells to the inflammatory focus and deuterium (2H) magnetic resonance spectroscopy (MRS) was used to monitor the metabolic fate of [6,6-2H2]glucose within the affected tissue. Histology and flow cytometry were used to validate the in vivo data. After plug implantation and intravenous administration of the 19F-containing contrast agent, 1H/19F MRI confirmed the infiltration of 19F-labeled immune cells into LPS-doped plugs while no 19F signal was observed in PBS-containing control plugs. Identification of the inflammatory focus was followed by i.p. bolus injection of deuterated glucose and continuous 2H MRS. Inflammation-induced alterations in metabolic fluxes could be tracked with an excellent temporal resolution of 2 min up to approximately 60 min after injection and demonstrated a more anaerobic glucose utilization in the initial phase of immune cell recruitment. 1H/2H/19F MRI/MRS was successfully employed for noninvasive monitoring of metabolic alterations in an inflammatory environment, paving the way for simultaneous in vivo registration of immunometabolic data in basic research and patients.

PKA regulatory subunit Bcy1 couples growth, lipid metabolism, and fermentation during anaerobic xylose growth in Saccharomyces cerevisiae.

Organisms have evolved elaborate physiological pathways that regulate growth, proliferation, metabolism, and stress response. These pathways must be properly coordinated to elicit the appropriate response to an ever-changing environment. While individual pathways have been well studied in a variety of model systems, there remains much to uncover about how pathways are integrated to produce systemic changes in a cell, especially in dynamic conditions. We previously showed that deletion of Protein Kinase A (PKA) regulatory subunit BCY1 can decouple growth and metabolism in Saccharomyces cerevisiae engineered for anaerobic xylose fermentation, allowing for robust fermentation in the absence of division. This provides an opportunity to understand how PKA signaling normally coordinates these processes. Here, we integrated transcriptomic, lipidomic, and phospho-proteomic responses upon a glucose to xylose shift across a series of strains with different genetic mutations promoting either coupled or decoupled xylose-dependent growth and metabolism. Together, results suggested that defects in lipid homeostasis limit growth in the bcy1Δ strain despite robust metabolism. To further understand this mechanism, we performed adaptive laboratory evolutions to re-evolve coupled growth and metabolism in the bcy1Δ parental strain. The evolved strain harbored mutations in PKA subunit TPK1 and lipid regulator OPI1, among other genes, and evolved changes in lipid profiles and gene expression. Deletion of the evolved opi1 gene partially reverted the strain's phenotype to the bcy1Δ parent, with reduced growth and robust xylose fermentation. We suggest several models for how cells coordinate growth, metabolism, and other responses in budding yeast and how restructuring these processes enables anaerobic xylose utilization.

Niche differentiation of microbial community shapes vertical distribution of recalcitrant dissolved organic matter in deep-sea sediments

Sedimentary organic matter provides carbon substrates and energy sources for microorganisms, which drive benthic biogeochemical processes and in turn modify the quantity and quality of dissolved organic matter (DOM). However, the molecular composition and distribution of DOM and its interactions with microbes in deep-sea sediments remain poorly understood. Here, molecular composition of DOM and its relationship with microbes were analyzed in samples collected from two sediment cores (∼40 cm below the sea floor), at depths of 1157 and 2253 m from the South China Sea. Results show that niche differentiation was observed on a fine scale in different sediment layers, with Proteobacteria and Nitrososphaeria dominating the shallow sediments (0–6 cm) and Chloroflexi and Bathyarchaeia prevailing in deeper sediments (6–40 cm), indicating correspondence of microbial community composition with both geographical isolation and the availability of organic matter. An intimate link between the DOM composition and microbial community further indicates that, microbial mineralization of fresh organic matter in the shallow layer potentially resulted in the accumulation of recalcitrant DOM (RDOM), while relatively low abundance of RDOM was linked to anaerobic microbial utilization in deeper sediment layers. In addition, higher RDOM abundance in the overlying water, as compared to that in the surface sediment, suggests that sediment might be a source of deep-sea RDOM. These results emphasize the close relation between the distribution of sediment DOM and different microbial community, laying a foundation for understanding the complex dynamics of RDOM in deep-sea sediment and water column.

Energy substrate metabolism, mitochondrial structure and oxidative stress after cardiac ischemia-reperfusion in mice lacking UCP3

Myocardial ischemia-reperfusion (IR) injury may result in cardiomyocyte dysfunction. Mitochondria play a critical role in cardiomyocyte recovery after IR injury. The mitochondrial uncoupling protein 3 (UCP3) has been proposed to reduce mitochondrial reactive oxygen species (ROS) production and to facilitate fatty acid oxidation. As both mechanisms might be protective following IR injury, we investigated functional, mitochondrial structural, and metabolic cardiac remodeling in wild-type mice and in mice lacking UCP3 (UCP3–KO) after IR. Results showed that infarct size in isolated perfused hearts subjected to IR ex vivo was larger in adult and old UCP3–KO mice than in equivalent wild-type mice, and was accompanied by higher levels of creatine kinase in the effluent and by more pronounced mitochondrial structural changes. The greater myocardial damage in UCP3–KO hearts was confirmed in vivo after coronary artery occlusion followed by reperfusion. S1QEL, a suppressor of superoxide generation from site IQ in complex I, limited infarct size in UCP3–KO hearts, pointing to exacerbated superoxide production as a possible cause of the damage. Metabolomics analysis of isolated perfused hearts confirmed the reported accumulation of succinate, xanthine and hypoxanthine during ischemia, and a shift to anaerobic glucose utilization, which all recovered upon reoxygenation. The metabolic response to ischemia and IR was similar in UCP3–KO and wild-type hearts, being lipid and energy metabolism the most affected pathways. Fatty acid oxidation and complex I (but not complex II) activity were equally impaired after IR. Overall, our results indicate that UCP3 deficiency promotes enhanced superoxide generation and mitochondrial structural changes that increase the vulnerability of the myocardium to IR injury.

Modeling methane yield potential and analysis of anaerobic co-digestion using mixed feedstock

The growing demand for sustainable and renewable energy sources has spurred interest in anaerobic co-digestion utilization as a promising technology for biogas production. This study presents a comprehensive investigation into the potential of methane yield and the analysis of anaerobic co-digestion using a mixture of diverse organic feedstock, including food waste, cow dung, canteen waste, chicken manure, and water. The research involved rigorous modeling and analysis of the co-digestion process, aiming to optimize biogas production while assessing its economic feasibility. The anaerobic digester's mixed feedstock is examined to understand its synergistic effects on methane generation. Subsequently, a series of anaerobic digestion simulations is conducted under various temperature conditions to evaluate the methane yield potential. The result demonstrates that more than 97% of biogas production capacity is achievable under thermophilic and mesophilic operating conditions compared to ambient conditions. Further economic incentive analysis suggests that more than 768 kWh of electricity production is obtainable through ambient operating conditions.

Distribution, organization and expression of genes concerned with anaerobic lactate utilization in human intestinal bacteria.

Lactate accumulation in the human gut is linked to a range of deleterious health impacts. However, lactate is consumed and converted to the beneficial short-chain fatty acids butyrate and propionate by indigenous lactate-utilizing bacteria. To better understand the underlying genetic basis for lactate utilization, transcriptomic analyses were performed for two prominent lactate-utilizing species from the human gut, Anaerobutyricum soehngenii and Coprococcus catus , during growth on lactate, hexose sugar or hexose plus lactate. In A. soehngenii L2-7 six genes of the lactate utilization (lct) cluster, including NAD-independent d-lactate dehydrogenase (d-iLDH), were co-ordinately upregulated during growth on equimolar d- and l-lactate (dl-lactate). Upregulated genes included an acyl-CoA dehydrogenase related to butyryl-CoA dehydrogenase, which may play a role in transferring reducing equivalents between reduction of crotonyl-CoA and oxidation of lactate. Genes upregulated in C. catus GD/7 included a six-gene cluster (lap) encoding propionyl CoA-transferase, a putative lactoyl-CoA epimerase, lactoyl-CoA dehydratase and lactate permease, and two unlinked acyl-CoA dehydrogenase genes that are candidates for acryloyl-CoA reductase. A d-iLDH homologue in C. catus is encoded by a separate, partial lct, gene cluster, but not upregulated on lactate. While C. catus converts three mols of dl-lactate via the acrylate pathway to two mols propionate and one mol acetate, some of the acetate can be re-used with additional lactate to produce butyrate. A key regulatory difference is that while glucose partially repressed lct cluster expression in A. soehngenii , there was no repression of lactate-utilization genes by fructose in the non-glucose utilizer C. catus . This suggests that these species could occupy different ecological niches for lactate utilization in the gut, which may be important factors to consider when developing lactate-utilizing bacteria as novel candidate probiotics.

Comparative Life Cycle Assessment Analysis of Sewage Sludge Recycling Systems in China

With the acceleration of economic development and urbanization in China, sewage sludge generation has sharply increased. To maximize energy regeneration and resource recovery, it is crucial to analyze the environmental impact and sustainability of different sewage sludge recycling systems based on life cycle assessment. This study analyzed four sewage sludge recycling systems in China through life cycle assessment using the ReCipe method, namely aerobic composting, anaerobic digestion and biomass utilization, incineration, and heat utilization and using for building materials. In particular, the key pollution processes and pollutants in sewage sludge recycling systems were analyzed. The results demonstrated that aerobic composting is the most environmentally optimal scenario for reducing emissions and energy consumption. The lowest environmental impact and operating costs were achieved by making bricks and using them as building materials; this was the optimal scenario for sludge treatment and recycling. In contrast, incineration and heat utilization had the highest impact on health and marine toxicity. Anaerobic digestion and biomass utilization had the highest impact on climate change, terrestrial acidification, photochemical oxidant formation, and particulate matter formation. In the future, policy designers should prioritize building material creation for sludge treatment and recycling.

Evaluation of Anaerobic Glucose Utilization by Escherichia coli Strains with Impaired Fermentation Ability during Respiration with External and Internal Electron Acceptors

Evaluation of Anaerobic Glucose Utilization by Escherichia coli Strains with Impaired Fermentation Ability during Respiration with External and Internal Electron Acceptors

Validity and Reliability of Hydraulic-Analogy Bioenergetic Models in Sprint Roller Skiing.

Purpose: To develop a method for individual parameter estimation of four hydraulic-analogy bioenergetic models and to assess the validity and reliability of these models’ prediction of aerobic and anaerobic metabolic utilization during sprint roller-skiing.Methods: Eleven elite cross-country skiers performed two treadmill roller-skiing time trials on a course consisting of three flat sections interspersed by two uphill sections. Aerobic and anaerobic metabolic rate contributions, external power output, and gross efficiency were determined. Two versions each (fixed or free maximal aerobic metabolic rate) of a two-tank hydraulic-analogy bioenergetic model (2TM-fixed and 2TM-free) and a more complex three-tank model (3TM-fixed and 3TM-free) were programmed into MATLAB. The aerobic metabolic rate (MRae) and the accumulated anaerobic energy expenditure (Ean,acc) from the first time trial (STT1) together with a gray-box model in MATLAB, were used to estimate the bioenergetic model parameters. Validity was assessed by simulation of each bioenergetic model using the estimated parameters from STT1 and the total metabolic rate (MRtot) in the second time trial (STT2).Results: The validity and reliability of the parameter estimation method based on STT1 revealed valid and reliable overall results for all the four models vs. measurement data with the 2TM-free model being the most valid. Mean differences in model-vs.-measured MRae ranged between -0.005 and 0.016 kW with typical errors between 0.002 and 0.009 kW. Mean differences in Ean,acc at STT termination ranged between −4.3 and 0.5 kJ and typical errors were between 0.6 and 2.1 kJ. The root mean square error (RMSE) for 2TM-free on the instantaneous STT1 data was 0.05 kW for MRae and 0.61 kJ for Ean,acc, which was lower than the other three models (all P < 0.05). Compared to the results in STT1, the validity and reliability of each individually adapted bioenergetic model was worse during STT2 with models underpredicting MRae and overpredicting Ean,acc vs. measurement data (all P < 0.05). Moreover, the 2TM-free had the lowest RMSEs during STT2.Conclusion: The 2TM-free provided the highest validity and reliability in MRae and Ean,acc for both the parameter estimation in STT1 and the model validity and reliability evaluation in the succeeding STT2.

Variations of heavy metals, nutrients, POPs and particle size distribution during “sludge anaerobic digestion-solar drying-land utilization process”: Case study in China

Sewage sludge was rich in pollutants such as heavy metals, nutrients and persistent organic pollutants. Anaerobic digestion can effectively degrade the pollutants while achieving sludge stabilization and reduction. This study took a sludge treatment plant located in Anhui Province, China as a case study, investigating the variations of multiple substances and particle size distribution during sludge anaerobic digestion-solar drying-land utilization process. The results demonstrated anaerobic digestion had a positive effect on the removal of heavy metals, nutrients and persistent organic pollutants, for polycyclic aromatic hydrocarbons, antibiotics and disinfection by-products with 41.38%, 62.26% and 68.68%, respectively, which were related to their molecular weight and structure. Large amounts of heavy metals would flow away with liquid digestate, in which Cr and Hg were the most and least, 90.44% and 41.95% respectively. The degradation of extracellular polymers in this process led to a decrease in particle size distribution, which caused the deterioration of sludge dewatering performance. Nutrients and water content increased and decreased respectively during solar drying along with the volatilization of organic matter under high temperature, which was beneficial for the final sludge product to subsequent land utilization. No significant correlation was demonstrated between heavy metals and sludge properties besides electrical conductivity. The study provided a new thinking on the variations of different substances and the way of actual treatment and disposal from the perspective of sludge anaerobic digestion-solar drying-land utilization process, which had a considerable significance for the further promotion and application of anaerobic digestion process in China's engineering community.

Bacterial Microcompartments Coupled with Extracellular Electron Transfer Drive the Anaerobic Utilization of Ethanolamine in Listeria monocytogenes.

ABSTRACTEthanolamine (EA) is a valuable microbial carbon and nitrogen source derived from cell membranes. EA catabolism is suggested to occur in a cellular metabolic subsystem called a bacterial microcompartment (BMC), and the activation of EA utilization (eut) genes is linked to bacterial pathogenesis. Despite reports showing that the activation of eut is regulated by a vitamin B12-binding riboswitch and that upregulation of eut genes occurs in mice, it remains unknown whether EA catabolism is BMC dependent in Listeria monocytogenes. Here, we provide evidence for BMC-dependent anaerobic EA utilization via metabolic analysis, proteomics, and electron microscopy. First, we show vitamin B12-induced activation of the eut operon in L. monocytogenes coupled to the utilization of EA, thereby enabling growth. Next, we demonstrate BMC formation connected with EA catabolism with the production of acetate and ethanol in a molar ratio of 2:1. Flux via the ATP-generating acetate branch causes an apparent redox imbalance due to the reduced regeneration of NAD+ in the ethanol branch resulting in a surplus of NADH. We hypothesize that the redox imbalance is compensated by linking eut BMCs to anaerobic flavin-based extracellular electron transfer (EET). Using L. monocytogenes wild-type, BMC mutant, and EET mutant strains, we demonstrate an interaction between BMCs and EET and provide evidence for a role of Fe3+ as an electron acceptor. Taken together, our results suggest an important role of BMC-dependent EA catabolism in L. monocytogenes growth in anaerobic environments like the human gastrointestinal tract, with a crucial role for the flavin-based EET system in redox balancing.IMPORTANCE Listeria monocytogenes is a foodborne pathogen causing severe illness, and as such, it is crucial to understand the molecular mechanisms contributing to pathogenicity. One carbon source that allows L. monocytogenes to grow in humans is ethanolamine (EA), which is derived from phospholipids present in eukaryotic cell membranes. It is hypothesized that EA utilization occurs in bacterial microcompartments (BMCs), self-assembling subcellular proteinaceous structures and analogs of eukaryotic organelles. Here, we demonstrate that BMC-driven utilization of EA in L. monocytogenes results in increased energy production essential for anaerobic growth. However, exploiting BMCs and the encapsulated metabolic pathways also requires the balancing of oxidative and reductive pathways. We now provide evidence that L. monocytogenes copes with this by linking BMC activity to flavin-based extracellular electron transfer (EET) using iron as an electron acceptor. Our results shed new light on an important molecular mechanism that enables L. monocytogenes to grow using host-derived phospholipid degradation products.

Study of the Potential of the Reversal of the Fatty-Acid Beta-Oxidation Pathway for Stereoselective Biosynthesis of (S)-1,3-Butanediol from Glucose by Recombinant Escherichia coli Strains

The possible contribution of collateral enzymes to the formation of the key precursor metabolite, 3-hydroxybutyryl-CoA, has been evaluated in a recombinant Escherichia coli strain engineered for 1,3-butanediol biosynthesis from glucose via the inverted fatty-acid beta-oxidation pathway. Inactivation of the 3-hydroxyadipyl-CoA dehydrogenase gene, paaH, did not prevent 1,3-butanol biosynthesis during anaerobic glucose utilization by a strain with an intact, essential gene, fabG. This gene encodes 3-ketoacyl-ACP reductase, which can catalyze the conversion of acetoacetyl-CoA to (R)-3-hydroxybutyryl-CoA. The subsequent inactivation in the strain of the fadB gene, which encodes (S)-stereospecific 3-hydroxyacyl-CoA dehydrogenase of the fatty-acid beta oxidation led to the cessation of 1,3-butanediol synthesis. The respective diol was also not found among the products secreted by the strain possessing the intact fabG and paaH genes upon the individual deletion of the fadB gene. It was established that the collateral enzymes did not participate in the formation of 3-hydroxybutyryl-CoA in the studied strains, and the respective CoA derivative was synthesized solely by the (S)-specific enzyme of the fatty-acid beta-oxidation pathway. The results indicate that reversal of the fatty-acid beta oxidation pathway can ensure the enantioselective biosynthesis of the (S)-stereoisomer of 1,3-butanediol in engineered E. coli strains.

THE UTILIZATION OF CARBON SOURCES MIXTURE (GLUCOSE, GLYCEROL AND FORMATE) AND GENERATION OF FERMENTATION END-PRODUCTS BY $ESCHERICHIA$ $COLI$

In this study anaerobic utilization of mixed carbon sources (glucose, glycerol, formate) and generation of fermentation end-products by Escherichia coli at slightly alkaline and slightly acidic pHs was investigated at the first time. It has been shown that E. coli is able to perform co-fermentation of glucose and glycerol in the presence of external formate. The latter was utilized by bacterial cells at first. Acetate is the permanent product (25–50 mM) during both glucose and glycerol utilization. It has been revealed that composition of fermentation end-products depends not only on external pH, but also on co-utilization of substrates.

Оценка анаэробной утилизации глюкозы штаммами Escherichia coli с нарушенной способностью к брожению при дыхании с внешним и внутренним акцептором электронов

The characteristics of anaerobic glucose utilization and metabolite production by recombinant Escherichia coli strains with impaired fermentation ability upon respiration with pyruvate as an internal and nitrate as an external electron acceptor have been studied. It was found that respiration processes utilizing pyruvic acid as an endogenous electron acceptor and leading to the lactate and alanine formation were capable of mutual interference. After elimination of ammonium ions from the medium, the native activity levels of respiratory lactate dehydrogenases Did and LldD in E. coli strains deficient in the mixed acid fermentation pathways can almost completely compensate for the loss of activity of respiratory alanine dehydrogenase DadA, but are insufficient to maintain the entire intracellular redox balance. The addition of nitrate ions in the medium abolished alanine production by the strains despite the availability of ammonium ions, while the functionality of respiratory reduction of endogenous pyruvate to lactate retained in the studied strains even in the presence of a strong exogenous oxidant. Respiration with external electron acceptor provoked the activation of the oxidative tricarboxylic acid cycle in the strains. Anaerobic glucose utilization by the strain with interrupted tricarboxylic acid cycle increased during nitrate respiration, but remained restricted by the excessive generation of reducing equivalents in the residual reactions of the cycle. Escherichia coli, glucose, fermentation, respiration, pyruvate, lactate, alanine, nitrate, ammonium. The work was supported by a grant from the Russian Foundation for Basic Research (project #18-04-01222).

Quantifying the effects of four weeks of low-volume high-intensity sprint interval training on V̇O2max through assessment of hemodynamics.

Sprint interval training is a popular workout modality. Studies have eluded to a positive effect on maximal oxygen uptake, however little is known about the mechanistic basis of this adaptation. Therefore, the purpose of this study was to determine the effects of a short-term high-intensity sprint interval training (SIT) intervention on V̇O2max through quantification of both the respiratory and hemodynamic responses. Thirty-six physically active participants undertook 4 weeks of either cycling-based SIT (8×20 s at 170% P-V̇O2max with 10 s recovery) or continuous exercise training (CET) (30 min at 70% P-V̇O2max) 3 times per week. V̇O2max, blood-based markers and hemodynamic responses were assessed pre and post the intervention period. V̇O2max was assessed using breath-by-breath open circuit spirometry, while hemodynamic responses were monitored using thoracic impedance cardiography. V̇O2max exhibited a non-significant 4.1% increase (ES=0.24) for SIT with 7.0% P=0.007 (ES=0.40) increase for CET. Hemodynamic responses (maximal cardiac output, maximal stroke volume) displayed non-significant responses for CET and SIT while a-vO2dif-max increased from 15.8±4.8 to 18.3±2.9 mL/100 mL) (P=0.02) (ES=0.63) in SIT. V̇O2max is a function of maximal cardiac output and a-vO2dif-max, so for a meaningful change to occur in cardiorespiratory fitness, there must be a concomitant increase in O2 delivery. This study demonstrates that a low volume SIT intervention evokes peripherally mediated responses (a-vO2dif) and anaerobic substrate utilization rather than O2 delivery components. Future works should address the time course of the responses and when assessing V̇O2max-based responses that due attention be given to the hemodynamic responses as means of quantification of the response.

Metabolic activity analyses demonstrate that Lokiarchaeon exhibits homoacetogenesis in sulfidic marine sediments.

The genomes of the Asgard superphylum of Archaea hold clues pertaining to the nature of the host cell that acquired the mitochondrion at the origin of eukaryotes1-4. Representatives of the Asgard candidate phylum Candidatus Lokiarchaeota (Lokiarchaeon) have the capacity for acetogenesis and fermentation5-7, but how their metabolic activity responds to environmental conditions is poorly understood. Here, we show that in anoxic Namibian shelf sediments, Lokiarchaeon gene expression levels are higher than those of bacterial phyla and increase with depth below the seafloor. Lokiarchaeon gene expression was significantly different across a hypoxic-sulfidic redox gradient, whereby genes involved in growth, fermentation and H2-dependent carbon fixation had the highest expression under the most reducing (sulfidic) conditions. Quantitative stable isotope probing revealed that anaerobic utilization of CO2 and diatomaceous extracellular polymeric substances by Lokiarchaeon was higher than the bacterial average, consistent with higher expression of Lokiarchaeon genes, including those involved in transport and fermentation of sugars and amino acids. The quantitative stable isotope probing and gene expression data demonstrate homoacetogenic activity of Candidatus Lokiarchaeota, whereby fermentative H2 production from organic substrates is coupled with the Wood-Ljungdahl carbon fixation pathway8. The high energetic efficiency provided by homoacetogenesis8 helps to explain the elevated metabolic activity of Lokiarchaeon in this anoxic, energy-limited setting.