Low pH Research Articles

Long-Term Effect of Different Cropping Systems on Soil Physico-chemical Properties of Soil: Environmental Implications and Sustainability

Rice (Oryza sativa L.)-wheat (Triticum aestivum L.) a dominant cropping system in Punjab Region, Northwestern India, overtime is believed to have negative effect on the soil and water quality. The present study was conducted in an ongoing long-term experiment at the research farm of the School of Organic Farming, Punjab Agricultural University, Ludhiana, to compare the effect of different cropping systems on soil physico-chemical properties. Ten treatments (cropping systems) were laid in a Randomized Complete Block Design (RCBD). The treatments were rice-wheat (CS1), maize-wheat (CS2), basmati rice-wheat-cowpea green manure (CS3), maize-mustard-cowpea green manure (CS4), maize-potato-spring groundnut (CS5), maize-peas-spring groundnut (CS6), maize+ cowpea (fodder)-maize fodder-oats fodder-sathi maize fodder (CS7), sorghum multicut fodder-barseem fodder (CS8), maize (cobs/fodder)-potato-onion (CS9), and baby corn-potato-okra (CS10). Soil samples were collected from four soil depths (0-7.5, 7.5-15, 15-22.5, and 22.5-30 cm) under each cropping system and analyzed for particles size, soil pH, EC, soil organic carbon, aggregate associated carbon, bulk density, porosity, water stable aggregates, MWD, and penetration resistance. Significantly lower soil pH was reported in CS4 and CS8 compared to other cropping systems. Soil EC was significantly higher in CS5 and CS10 while lowest in CS4. Soil organic carbon (SOC), aggregate-associated carbon (AAC), and mean weight diameter (MWD) were significantly higher in CS7 and CS4. Soil bulk density (BD) and penetration resistance (PR) were significantly higher in CS1 and lowest in CS4. SOC was 19% higher in CS7 and BD was 16% lower in CS4 compared to CS1. Soil porosity and water-stable aggregates (WSA) were also found significantly higher in CS4 and CS7 whereas lowest in CS1. The increase in soil depths significantly increased the soil pH, BD and PR, whereas decreased the soil EC, SOC, AAC, porosity, MWD, and WSA. The cropping systems (CS4, CS7, CS8, CS6, CS5, CS3) with green manure/legume/fodder crops in rotation resulted in better physico-chemical properties through the addition of organic matter to the soil compared to cereal-cereal rotations.

Assessment of Soil Organic Matter and Its Microbial Role in Selected Locations in the South Bohemia Region (Czech Republic)

Organic matter has a very important function in soil, without which, soil formation processes cannot take place properly. It can be divided and classified based on several aspects; the most general division is between the living and non-living parts of organic matter. The results presented in this paper specifically refer to the living microbial part of organic matter. This research was carried out in the years 2021–2024 in the South Bohemia region located in the Czech Republic. Two types of land use (four permanent grassland areas, two forest areas) were evaluated. Based on laboratory soil analyses, some significant dependencies were found. For example, in grasslands with statistically identical pH, there was a dependence (p-value 0.05) between soil organic carbon (SOC), carbon of microbial biomass (MBC) and microbial basal respiration (MBR). Additionally, coniferous forest experimental locations had a lower pH, which, in turn, slowed the activity of microorganisms and promoted the accumulation of SOC in the soil. The results from this experiment support the current knowledge of organic matter and are important for a better understanding of the soil organic matter cycle.

Kaposi's sarcoma-associated herpesvirus (KSHV) gB dictates a low-pH endocytotic entry pathway as revealed by a dual-fluorescent virus system and a rhesus monkey rhadinovirus expressing KSHV gB.

Interaction with host cell receptors initiates internalization of Kaposi's sarcoma-associated herpesvirus (KSHV) particles. Fusion of viral and host cell membranes, which is followed by release of the viral capsid into the cytoplasm, is executed by the core fusion machinery composed of glycoproteins H (gH), L (gL), and B (gB), that is common to all herpesviruses. KSHV infection has been shown to be sensitive to inhibitors of vacuolar acidification, suggestive of low pH as a fusion trigger. To analyze KSHV entry at the single particle level we developed dual-fluorescent recombinant KSHV strains that incorporate fluorescent protein-tagged glycoproteins and capsid proteins. In addition, we generated a hybrid rhesus monkey rhadinovirus (RRV) that expresses KSHV gB in place of RRV gB to analyze gB-dependent differences in infection pathways. We demonstrated lytic reactivation and infectivity of dual-fluorescent KSHV. Confocal microscopy was used to quantify co-localization of fluorescently-tagged glycoproteins and capsid proteins. Using the ratio of dual-positive KSHV particles to single-positive capsids as an indicator of fusion events we established KSHV fusion kinetics upon infection of different target cells with marked differences in the "time-to-fusion" between cell types. Inhibition of vesicle acidification prevented KSHV particle-cell fusion, implicating low vesicle pH as a requirement. These findings were corroborated by comparison of RRV-YFP wildtype reporter virus and RRV-YFP encoding KSHV gB in place of RRV gB. While RRV wt infection of receptor-overexpressing cells was unaffected by inhibition of vesicle acidification, RRV-YFP expressing KSHV gB was sensitive to Bafilomycin A1, an inhibitor of vacuolar acidification. Single- and dual-fluorescent KSHV strains eliminate the need for virus-specific antibodies and enable the tracking of single viral particles during entry and fusion. Together with a hybrid RRV expressing KSHV gB and classical fusion assays, these novel tools identify low vesicle pH as an endocytotic trigger for KSHV membrane fusion.

Predictors and Outcomes of Extubation Failure in Preterm Neonates: A Systematic Review.

Extubation failure (EF) is common in preterm neonates and may be associated with adverse outcomes. To systematically review and meta-analyze the existing literature on predictors and outcomes of EF in preterm neonates. MEDLINE, Epub Ahead of Print, In-Process & Other Non-Indexed Citations, Embase (OvidSP), CINAHL (EBSCOHost), and Cochrane Library (Wiley) from 1995 onward. The search strategy was developed by a reference librarian. Experimental or observational studies reporting on predictors and/or outcomes related to EF (defined as reintubation within 7days) in preterm neonates less than 37weeks were eligible. Predictors included machine learning (ML) algorithms and lung ultrasound (LUS). Main outcome of interest was association of EF with mortality and/or bronchopulmonary dysplasia (BPD). Studies identified by the search strategy were screened based on title and abstract. Data from included studies were extracted independently by 2 authors, along with adjudication of risk of bias. RevMan Web was used to conduct meta-analyses. Out of 8336 studies screened, 120 were included. Neonates with lower gestational age at birth, birthweight, postmenstrual age, and weight at extubation were more likely to experience EF. Higher level of pre-extubation respiratory support, indicated by lower pre-extubation pH and higher pre-extubation mean airway pressure, fraction of inspired oxygen, and Pco2 were associated with EF risk. ML models showed variable accuracy and lower external validity. LUS may be a promising predictor, though scoring systems varied. EF was associated with higher odds of mortality and/or BPD (pooled odds ratio [OR], 4.7; 95% CI, 2.84-7.76) as well as the individual components of the composite: mortality (pooled OR, 3.87; 95% CI, 2.35-6.36) and BPD (pooled OR, 3.27; 95% CI, 2.54-4.21). Associations were derived from unadjusted data, precluding a definitive causal relationship between EF and predictors/outcomes. Lower gestational and chronological age and higher levels of pre-extubation ventilation support were associated with EF. ML models and LUS scores require further validation in larger studies. EF was associated with mortality and/or BPD.

How tailor-made copolymers can control the structure and properties of hybrid nanomaterials: the case of polyionic complexes.

Hybrid polyionic complexes (HPICs) are colloidal structures with a charged core rich in metal ions and a neutral hydrophilic corona. Their properties, whether as reservoirs or catalysts, depend on the accessibility and environment of the metal ions. This study demonstrates that modifying the coordination sphere of these ions can tune the properties of HPICs by altering the composition of the complexing block or varying formulation conditions. Hence, double hydrophilic block copolymers were synthesized using RAFT polymerization, with polyethylene glycol as the neutral block and different ratios of acrylic acid (AA) and vinylphosphonic acid (VPA) as the functional block and further complexed with Fe(III) ions. The resulting iron-based HPICs with higher VPA content were more stable at low pH due to stronger VPA-iron interactions, but their catalytic efficiency in the photo-Fenton process decreased at higher pH. In nanoparticle synthesis, polymers with higher VPA content produced smaller, less-defined Prussian blue nanoparticles, while a 50/50 AA/VPA ratio resulted in uniform nanoparticles and optimal reactivity. Multivariate analysis revealed that not only composition but also local structural organization impacts HPIC properties, influenced by changes in the complexing block structure (e.g., statistical, block) or formulation conditions.

Vaping-associated mechanisms of gastroesophageal reflux disease development

BACKGROUND: There is convincing evidence of the negative impact of vaping on the respiratory and cardiovascular systems. In addition, it is advisable to evaluate the gastroenterological aspects of smoking electronic cigarettes. AIM: To assess the impact of vaping on the functional state of the gastroesophageal zone in healthy people compared to patients suffering from gastroesophageal reflux disease. MATERIAL AND METHODS: The study included 90 patients, divided into three groups of 30 people. The first group consisted of individuals without gastrointestinal diseases, regularly (more than 12 months) smoking vapes. Patients of the 2nd group suffered from gastroesophageal reflux disease. The 3rd group (control) included healthy individuals without bad habits. Using validated questionnaires, clinical manifestations of reflux syndrome were assessed, daily pH-impedancemetry was performed, and serum gastrin and motilin levels were studied. Statistical processing was performed using the Kruskal-Wallis criterion and the Dunn test. Fisher's exact test was used to compare qualitative features, and the Spearman correlation coefficient was used to assess dependencies. The study established a significance criterion of p 0.05. RESULTS: In the 2nd group, along with symptoms of reflux disease, a low pH level of the esophagus lower third and a high daily number of all types of reflux were recorded. In this group, in comparison with the control group, a low level of motilin in the blood was detected (83.2 [56.9; 99.3] pg/ml and 189.7 [117.6; 362.3] pg/ml, respectively, p=0.001). In the group of vapers, compared with healthy controls, a greater severity of reflux syndrome and an increase in the daily number of acidic (54 [39.5; 71] and 21.5 [18; 28.8], respectively, p=0.001) and weakly acidic (7.5 [4.3; 9.8] and 2 [1; 3], respectively, p=0.001) refluxes were recorded, against the background of a decrease in the pH level in the esophagus (4.7 [4.1; 5.9] and 6.7 [6.2; 6.8], respectively, p=0.001). CONCLUSION: Vaping is accompanied by an increase in the number of gastroesophageal refluxes, probably due to inhibition of the motility of the lower esophageal sphincter and can contribute to the development of gastroesophageal reflux disease.

Isolation and Characterization of Lactic Acid Bacteria: A Strategy to Produce Inoculum for Forage Ensiling

Purpose: Sri Lankan dairy sector faces challenges due to seasonal variability and suboptimal quality of forage for dairy cattle feeding. While silage offers year-round availability of forage, concerns arise regarding potential quality degradation during forage ensiling. Microbial inoculants are utilized to expedite the ensiling and minimize quality deterioration. This study involves the isolation and characterization of lactic acid bacteria (LAB) from silage, with the aim of identifying potential candidates to be used as silage inoculants.Research Method: Lactobacillus were isolated from 10 silage samples of each forage type: sorghum, maize, and guinea grass. They were characterized using the 16S rRNA gene sequencing procedure. The anaerobic sugar fermentation ability of the isolated LAB was evaluated by inoculating them into sterilized sugar solutions, and measuring the titratable acidity (TA) and pH value over time.Findings: The isolates were identified to be non-motile, non-spore-forming and Gram-positive rods. Further, they tested negative for catalase, triple sugar iron, citrate, urease, indole, gelatine hydrolysis, motility, and oxidase tests. The LAB isolated from guinea grass, sorghum, and maize corresponded to Lactobacillus oris, Lactobacillus rhamnosus, and Lactobacillus plantarum, respectively. The TA in all inoculated solutions was higher compared to the control (0.55-0.66% vs. 0.48%), with L. plantarum showing the highest TA (0.66%) at 30 hours incubation. Additionally, all sugar solutions treated with LAB isolates exhibited a lower pH value at 30 hours compared to the control (4.70-5.07 vs. 5.75). Notably, L. plantarum demonstrated the most significant pH value reduction at 18 hours (5.85 vs. 6.29-6.64).Value: Lactobacillus oris, L. rhamnosus, and L. plantarum, isolated from guinea grass, sorghum, and maize silage, respectively, have the potential to be developed as inoculants for ensiling forage.

Highly Tension-Strained Copper Concentrates Diluted Cations for Selective Proton-Exchange Membrane CO2 Electrolysis.

Electrolysis of carbon dioxide (CO2) in acid offers a promising route to overcome CO2 loss in alkaline and neutral electrolytes, but requires concentrated alkali cations (typical ≥3 M) to mitigate the trade-off between low pH and high hydrogen evolution reaction (HER) rate, causing salt precipitation. Here we report a strategy to resolve this problem by introducing tensile strain in a copper (Cu) catalyst, which can selectively reduce CO2 to valuable multicarbon products, particularly ethylene, in a pH 1 electrolyte with 1 M potassium ions. We find that the tension-strained Cu creates an electron-rich surface that concentrates diluted potassium ions, contributing to CO2 activation and HER suppression. With this catalyst, we show constant ethylene Faradaic efficiency (FE) of 44.3% over 100 hours at 400 mA cm-2 and a cell voltage of 3.1 volts in a proton-exchange membrane electrolyser. Moreover, selective electrosynthesis of ethylene oxide using the as-produced ethylene was demonstrated in an integrated system.

Highly Tension‐Strained Copper Concentrates Diluted Cations for Selective Proton‐Exchange Membrane CO2 Electrolysis

Electrolysis of carbon dioxide (CO2) in acid offers a promising route to overcome CO2 loss in alkaline and neutral electrolytes, but requires concentrated alkali cations (typical ≥3 M) to mitigate the trade‐off between low pH and high hydrogen evolution reaction (HER) rate, causing salt precipitation. Here we report a strategy to resolve this problem by introducing tensile strain in a copper (Cu) catalyst, which can selectively reduce CO2 to valuable multicarbon products, particularly ethylene, in a pH 1 electrolyte with 1 M potassium ions. We find that the tension‐strained Cu creates an electron‐rich surface that concentrates diluted potassium ions, contributing to CO2 activation and HER suppression. With this catalyst, we show constant ethylene Faradaic efficiency (FE) of 44.3% over 100 hours at 400 mA cm‐2 and a cell voltage of 3.1 volts in a proton‐exchange membrane electrolyser. Moreover, selective electrosynthesis of ethylene oxide using the as‐produced ethylene was demonstrated in an integrated system.

Probiotic Characterization of Lactic Acid Bacteria from Donkey Feces in China

Probiotics are beneficial to humans and animals and often used for regulating immunity, intestinal microbiota balance, and animal growth performance. Donkey husbandry has boomed in China in recent years and there is an urgent need for probiotics effective for improving donkey health. However, studies on potential probiotic strains isolated from donkeys are scarce. This project aimed to screen LAB strains from donkey feces, detect their antimicrobial activity and evaluate their probiotic characteristics in vitro. Thirteen LAB isolates showed different degrees of antimicrobial activity against four indicator bacteria: three common pathogens (Escherichia coli, Staphylococcus aureus, and Salmonella typhimurium) and one pathogen restricted to equines (Salmonella. abortus equi), eight of which could inhibit all four pathogens. Seven isolates showed higher tolerance to low pH and bile salts, with >50% and >60% survival rates, respectively. Five of them had more than 50% survival rate to artificial gastric and intestinal fluids. Only three isolates possessed good properties, with >40% auto-aggregation, >40% hydrophobicity, and high co-aggregation with the indicator pathogens. An L9 isolate, identified as Ligilactobacillus salivarius, was sensitive to most antibiotics tested. Overall, these results indicate that the L. salivarius L9 isolate meets the requirements of the probiotics selection criteria in vitro and can potentially be developed as a probiotic for donkeys.

Lactic Acid Bacteria from Northern Thai (Lanna) Fermented Foods: A Promising Source of Probiotics with Applications in Synbiotic Formulation

Northern Thai culture offers a rich variety of traditional fermented foods beneficial for gastrointestinal health. In this study, we characterized lactic acid bacteria (LAB) from various indigenous fermented foods as potential probiotic candidates and determined their properties for application in commercial synbiotic formulation. Five isolates demonstrating high tolerance to low pH (2.0) and 0.3% bile salts were collected and characterized. These included three strains of Lactiplantibacillus plantarum isolated from nham (NB1, NP2, and NP11) and two strains of Limosilactobacillus fermentum isolated from pla-som (PS4 and PS7). All the selected LAB isolates exhibited γ-hemolytic activity, strong antimicrobial activity, and high resistance to gastric and duodenal digestion conditions. Among the LAB isolates, L. plantarum NB1 demonstrated the highest capacity for adhesion to Caco-2 cells, auto-aggregation, and antioxidant activity, differing significantly (p < 0.05) from the other isolates. Furthermore, the NB1 strain exhibited preferential growth in the presence of commercial prebiotics (fructooligosaccharide, lactose, and inulin) and good survival after lyophilization, which is a desirable characteristic for a powdered ingredient. Therefore, the NB1 strain is a suitable probiotic candidate for applications in synbiotic formulation or as a functional food ingredient.

Experimental and Theoretical Study of Delivering Metformin Anti‐Lung Cancer Drug With Aluminum Nitride Nanoparticles

ABSTRACTAluminum nitride (ALN) finds extensive application across various fields, and further advancement is undergoing to explore efficiency of this compound in drug delivery. The significance of this research lies in its contribution to nano‐based drug delivery systems for anticancer treatments. This study focuses on the preparation of ALN nanoparticle using a simple and cost‐effective route in an NH3 atmosphere and in the presence of hydrated aluminum chloride. The characterization techniques such as FT‐IR, TEM, SEM, UV, XRD, XPS, and EDS are used to analyze the synthesized nanoparticles. Then, metformin is incorporated into the fabricated nanostructure to achieve a drug loading of ~67%, demonstrating effectiveness of the selected nanocarrier for encapsulating this important drug. The specific impact of pH and time duration on the release profile of metformin highlights the versatility and potential applicability of ALN delivery system. Moreover, the gradual release of drug under physiological conditions (pH 7.4) as well as the accelerated release at the lower pH of 5.1 within 48 h proofed the responsiveness of the nanostructure to varying environmental conditions. Finally, a density functional theory (DFT) calculation was carried out to investigate adsorption of metformin. These computational analyses validated again the potential of ALN as an effective sensor for detecting metformin in biological systems. The unique characteristics of this study involve introducing a pH‐responsive nanocarrier to release drug selectively in response to pH of the environment, using a nanoparticle with sufficient stability that improves solubility of poorly soluble metformin. This bioavailable drug delivery system can reduce off‐target effects and toxicity associated with conventional drug therapies.

Therapeutic Effect of a Near‐Infrared Responsive MTX‐Mn3O4@PDA Nano‐Delivery System on Rheumatoid Arthritis

AbstractRheumatoid arthritis (RA) is an autoimmune disease associated with chronic inflammatory processes. RA, which is typically associated with the accumulation of hyperactive immune cells (HICs), particularly M1 proinflammatory macrophages, is accompanied by elevated levels of reactive oxygen species (ROS) and decreased pH in the synovial membranes of the joints. In this work, a nano‐delivery system (MTX‐Mn3O4@PDA) is designed that can deliver photothermal materials, ROS scavengers, and synovial fibroblast inhibitors at the joint site for the treatment of RA. After injecting MTX‐Mn3O4@PDA into the inflamed site of RA, photothermal therapy is initiated by near‐infrared (NIR) laser irradiation, which resulted in the death of activated inflammatory cells at the lesion site. While polydopamine (PDA) slowly dissociates under stimulation by a low pH microenvironment. Subsequently, excess ROS interacts with the Mn3O4 nanozyme and the undissociated PDA nanozyme, promoting ROS clearance, while Methotrexate (MTX) inhibits the proliferation of synovial fibroblasts. Intra‐articular injection of MTX‐Mn3O4@PDA (7 mg kg−1) into collagen‐induced arthritis mice demonstrated efficacy in reducing toe swelling and significantly alleviating synovial inflammation, bone erosion, and cartilage degeneration. This nano‐delivery system has potential clinical applications for treating RA.

Cascade-Responsive Nanoparticles for Efficient CRISPR/Cas9-Based Glioblastoma Gene Therapy.

CRISPR/Cas9 (CRISPR, clustered regularly interspaced short palindromic repeats) gene editing technology represents great promise for treating glioblastoma (GBM) due to its potential to permanently eliminate tumor pathogenic genes. Unfortunately, delivering CRISPR to the GBM in a safe and effective manner is challenging. Herein, a glycosylated and cascade-responsive nanoparticle (GCNP) that can effectively cross the blood-brain barrier (BBB) and activate CRISPR/Cas9-based gene editing only in the GBM is designed. The GCNP possesses a cationic polyplex core and a glycosylated polymer layer that is capable of cascading response to low pH and high GSH concentration, so that the release of CRISPR/Cas9 only takes place after crossing the BBB and entering the GBM where the acidic tumor microenvironment and high concentration of glutathione (GSH) are present. By targeting the programmed death-ligand 1 (PD-L1) in GBM, GCNP effectively inhibited the tumor growth and greatly prolonged the survival time of GBM-bearing mice when combined with temozolomide (TMZ).

Non-conventional yeasts: promising cell factories for organic acid bioproduction.

Microbial production of organic acids has been hindered by the poor acid tolerance of microorganisms and the high costs of waste salt reprocessing. The robustness of non-conventional microorganisms in an acidic environment makes it possible to produce organic acids at low pH and greatly simplifies downstream processing. In this review we discuss the environmental adaptability features of non-conventional yeasts, as well as the latest developments in genomic engineering strategies that have facilitated metabolic engineering of these strains. We also use selected examples of three-carbon (C3), C4, and C6 organic acids to illustrate the ongoing efforts and challenges of using non-conventional yeasts for organic acid production. This review provides theoretical guidance for the construction of highly robust organic acid producers.

PH Controlled Transient Cyclization of Peptides for Increased Stability towards Oral Delivery.

Peptides are highly efficient for treatment of many diseases, especially in oncology and diabetes. Oral delivery of peptides is desirable, but is challenged by low bioavailability and new chemical methods to enable oral delivery are needed. Here, we developed pH responsive linearization as a strategy for transient protection of peptides to extend their half-life in model systems. Peptides were cyclized to increase their stability at the low pH in the stomach, while they linearize at neutral pH to form the active peptide. We developed ester based responsive linkers with a protonable amine for O-to-N acyl shift, which allowed linearization strategies based on pyroglutamoyl (pGlu) or diketopiperazine (DKP) formation. After coupling of the linker, peptides were cyclized by CuAAC. We studied the stability against simulated gastric fluid (SGF) at different pH and the ability of cyclic peptides to linearize. This led to PYY3-36 analogues with pH responsive linearization for increased stability.

Aeration promotes Proteobacteria over Firmicutes in macerated food waste resulting in superior anaerobic digestion efficiency.

Aeration is a common pretreatment method to enhance biogas production via anaerobic digestion of waste organic feedstocks such as unused food. While impacts on downstream anaerobic digestion have been intensively investigated, the consequence of aeration on the microbial community in food waste has not been characterised. Food waste has a low pH resulting from the dominance of lactic acid bacteria within the Firmicutes phylum. This excludes other phylotypes with a higher potential to hydrolyse complex biopolymers in food waste. In this study we reveal that aeration of macerated food waste results in a dramatic shift away from Firmicutes towards dominance of Proteobacteria that are better known for extracellular enzyme production. Given that hydrolysis is the rate limiting step in anaerobic digestion, this explains why aeration improves the efficiency of biogas production from food waste. The discovery that Proteobacteria dominate microbial communities in aerated food waste opens up opportunities to manipulate extracellular enzyme production through gene expression mechanisms common among Proteobacteria such as quorum sensing.

Biocatalytic conversion of carbon dioxide to formate using a robust metal-independent Thiobacillus formate dehydrogenase

The capture and utilization of CO2 from industrial off-gases to produce commodity chemicals has the potential to make an important contribution to the transition to a circular economy. Formate, and its conjugate formic acid, is a potential sustainable platform chemical that can be produced from CO2. Electrochemical reduction of CO2 to formate is a promising route, but biocatalysis with formate dehydrogenase (FDH) as biocatalyst may offer advantages for industrial implementation such as mild conditions, high product selectivity, and less expensive down-stream processing. Here, we investigated the potential of a metal-independent Thiobacillus FDH (TsFDH) as a biocatalyst for the production of formate from CO2-rich industrial offgases. An excellent stability was demonstrated, also in the presence of potential off-gas impurities. A formate titer of 14 mM could be achieved at pH 6.5 and 37 °C, with an initial specific productivity of 0.37 mmol g−1 FDH h−1. TsFDH compares favorably to metal-dependent FDHs with respect to stability, O2-sensitivity and activity at low pH values, but unfavorably in terms of CO2 reduction activity, hampering its potential as industrial biocatalyst. Specific rates could be significantly improved by further reaction engineering, and possibly also by enzyme engineering.

Presence of Humic Acids in Landfill Leachate and Treatment by Flocculation at Low pH to Reduce High Pollution of This Liquid

Humic substances are abundant in landfill leachate, especially humic acids, which are insoluble at low pH in aqueous solutions. Focusing on the chemical properties of humic acids, we describe in this work a new method for a sustainable treatment of landfill leachate originated from solid wastes, which consists of the reduction of organic load (COD, chemical oxygen demand) and colour and is based in the gradual decrease in pH to the value in which HAs are insoluble in water solution. Zeta potential values mark the chemical stage of humic acids because of ionisation–protonation of the phenolic and carboxylic groups, and this parameter is monitored during flocculation, changing from −16.8 mV at pH 7.7 to 0.0068 mV at pH 2.0, when HAs precipitate. The final result is the reduction in the organic matter content (COD) and colour in the leachate, 86.1% and 84.7%, respectively. Solids produced by precipitation during the acidification treatment have been characterized by elemental chemical analysis and Fourier transform infrared spectrometry, concluding a high similarity in chemical composition with commercial and natural humic acids. Protonated humic acids at low pH can interact with other molecules by hydrogen bonds and form bigger molecular structures much more unstable in suspension, which conduct to precipitation. The mean diameter of the humic acids aggregates was measured, detecting the formation of big molecular structures at low pH. This process is analysed and compared economically with other processes proposed for landfill leachate treatment, resulting in a promising technique for the management of this residue.

The effect of environmental factors on transepithelial potential in a model Amazonian teleost, the tambaqui (Colossoma macropomum): Implications for sodium balance in harsh environments.

The tambaqui (Colossoma macropomum, G. Cuvier 1818) thrives both in the ion-poor waters of the Amazon and in commercial aquaculture. In both, environmental conditions can be harsh due to low ion levels, occasional high salt challenges (in aquaculture), low pH, extreme PO2 levels (hypoxia and hyperoxia), high PCO2 levels (hypercapnia), high ammonia levels (in aquaculture), and high and low temperatures. Ion transport across the gill is affected by active transport processes, passive diffusive permeability, ion concentrations (the chemical gradient), and transepithelial potential (TEP, the electrical gradient). The latter is a very important indicator of ionoregulatory status but is rarely measured. Using normoxic, normocapnic, ion-poor, low-dissolved organic carbon (DOC) well water (27°C, pH 7.0) as the acclimation and reference condition, we first confirmed that the strongly negative TEP (-22.3 mV inside relative to the external water) is a simple diffusion potential. We then evaluated the effects on TEP of more complex waters from the Rio Negro (strong hyperpolarization) and Rio Solimões (no significant change). Additionally, we have quantified significant effects of acute, realistic changes in environmental conditions-low pH (depolarization), hypercapnia (depolarization), hypoxia (depolarization), hyperoxia (hyperpolarization), elevated NaCl concentrations (depolarization), and elevated NH4Cl concentrations (depolarization). The TEP responses help explain many of the changes in net Na+ flux rates reported in the literature. We have also shown marked effects of temperature on TEP and unidirectional Na+ flux rates (hyperpolarization and decreased fluxes at 21°C, depolarization and increased fluxes at 33°C) with no changes in net Na+ flux rates. Calculations based on the Nernst equation demonstrate the importance of the TEP changes in maintaining net Na+ balance.