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This paper presents a modified fractional-order model (FOM) for microorganism stimulation in an up-flow anaerobic sludge blanket (UASB) reactor treating low-strength wastewater. This study aimed to examine the famine period of methanogens due to biomass accumulation in the UASB reactor over long time periods at a constant organic loading rate (OLR). This modified model can investigate the substrate biodegradation in a UASB reactor while considering substrate diffusion into biological granules during the feast and famine periods of methanogens. The Grünwald-Letnikov numerical technique was used to indicate the effect of biomass degradation on the biogas production rate and substrate biodegradation in a UASB reactor installed at Zenein Wastewater Treatment Plant (WWTP) in Giza, Egypt. Several fractional orders were applied in the dynamic model at biomass concentrations of 20 and 4 k g / m 3 in the reactor bed and blanket zones, respectively. An OLR of 0.9 k g C O D / m 3 / d a y using the calibrated kinetic parameters at 11 ∘ C was applied to comply with the experimental outcomes. The simulation results indicate that the removal efficiency of chemical oxygen demand (COD) was maintained at approximately 55 - 65 % , whereas the biogas production rate declined from 0.35 to 0.05 m 3 C H 4 / k g C O D r in the reactor bed zone due to a decline in food to microorganism (F/M) ratio from 0.04 to 0.018 d - 1 during the sludge retention time (SRT) in the UASB reactor. [ABSTRACT FROM AUTHOR]

Four new X-ray structures of tryptophan synthase (TS) crystallized with varying numbers of the amphipathic N-(4'-trifluoromethoxybenzoyl)-2-aminoethyl phosphate (F6) molecule are presented. These structures show one of the F6 ligands threaded into the tunnel from the β-site and reveal a distinct hydrophobic region. Over this expanse, the interactions between F6 and the tunnel are primarily nonpolar, while the F6 phosphoryl group fits into a polar pocket of the β-subunit active site. Further examination of TS structures reveals that one portion of the tunnel (T1) binds clusters of water molecules, whereas waters are not observed in the nonpolar F6 binding region of the tunnel (T2). MD simulation of another TS structure with an unobstructed tunnel also indicates the T2 region of the tunnel excludes water, consistent with a dewetted state that presents a significant barrier to the transfer of water into the closed β-site. We conclude that hydrophobic molecules can freely diffuse between the α- and β-sites via the tunnel, while water does not. We propose that exclusion of water serves to inhibit reaction of water with the α-aminoacrylate intermediate to form ammonium ion and pyruvate, a deleterious side reaction in the αβ-catalytic cycle. Finally, while most TS structures show βPhe280 partially blocking the tunnel between the α- and β-sites, new structures show an open tunnel, suggesting the flexibility of the βPhe280 side chain. Flexible docking studies and MD simulations confirm that the dynamic behavior of βPhe280 allows unhindered transfer of indole through the tunnel, therefore excluding a gating role for this residue.

The size of the gel preparation, the concentration of the encapsulated enzyme and the ratio of the preparation volume to the volume of the reaction mixture influence the reaction efficiency with encapsulated biocatalysts. A model of first order enzymatic reaction with substrate diffusion is presented and validated by the decomposition reaction of hydrogen peroxide by catalase. The Thiele modulus (Ф) contains the modified (including the enzyme concentration) enzymatic reaction constant (k′). Based on the model analysis, the Thiele modulus should not exceed a value of 2 (optimally less than 0.5). This value can be controlled by appropriate selection of the enzyme concentration inside and the size of the capsule. A lower Ф value gives a flat substrate concentration profile inside the gel capsule and all the enzyme molecules are involved in the reaction. The optimal diameter of the gel capsule with respect to their separation from the reaction mixture is 1–2 mm.

A generalized low-order model of the biofilm in a microbial fuel cell (MFC), suitable for use in real-time engineering applications, is presented. It is based on the description of the charge transfer, diffusion process, and charge accumulation in the biofilm. Since the dynamic processes in an MFC are ruled mainly by the biofilm, it can be used for many different diffusion-based MFC types by just changing the boundary conditions. Different mode operations like batch, fed-batch, continuous, etc., are also possible. The time-responses of voltage, substrate concentration on the surface of the electrode, and Faradaic and capacitive currents have been tested under several experimental conditions. [ABSTRACT FROM AUTHOR]

Soil structure and interactions between biotic and abiotic processes are increasingly recognized as important for explaining the large uncertainties in the outputs of macroscopic SOM decomposition models. We present a numerical analysis to assess the role of meso- and macropore topology on the biodegradation of a soluble carbon substrate in variably water saturated and pure diffusion conditions . Our analysis was built as a complete factorial design and used a new 3D pore-scale model, LBioS, that couples a diffusion lattice-Boltzmann model and a compartmental biodegradation model. The scenarios combined contrasted modalities of four factors: meso- and macropore space geometry, water saturation, bacterial distribution and physiology. A global sensitivity analysis of these factors highlighted the role of physical factors in the biodegradation kinetics of our scenarios. Bacteria location explained 28% of the total variance in substrate concentration in all scenarios, while the interactions among location, saturation and geometry explained up to 51% of it. [ABSTRACT FROM AUTHOR]

To interpret the response of ammonia oxidation to changing soil moisture, we conducted a batch aerobic incubation with a loam soil at different soil water potentials (SWP) from −1100 to −11 kPa, and calculated net nitrification rates and apparent isotope fractionation factors (αs/p). With increasing SWP, net nitrification rates increased from 2.3 to 9.8 mg N kg−1 d−1, while αs/p increased from 1.025 to 1.031 at field-capacity (SWP of −33 kPa) but decreased with increasing SWP above field capacity. The increased αs/p at field-capacity indicated that intracellular NH4+ concentration increased as a result of NH4+ supply exceeding NH3 oxidation, while NH3 oxidation exceeding NH4+ supply above field-capacity resulted in both decreased intracellular NH4+ concentration and αs/p. Our results suggest that NH4+ diffusion contributes more sensitively to increasing SWP than NH3 oxidation below field-capacity, while the reverse is the case above field-capacity. [ABSTRACT FROM AUTHOR]

Abstract: Scaling-up of microbial fuel cells (MFCs) for practical applications requires compact, multiple-electrode designs. Two possible configurations are a separator electrode assembly (SEA) or closely spaced electrodes (SPA) that lack a separator. It is shown here that the optimal configuration depends on whether the goal is power production or rate of wastewater treatment. SEA MFCs produced a 16% higher maximum power density (328 ± 11 mW m−2) than SPA MFCs (282 ± 29 mW m−2), and higher coulombic efficiencies (SEAs, 9–31%; SPAs, 2–23%) with domestic wastewater. However, treatment was accomplished in only 12 h with the SPA MFC, compared to 36 h with the SEA configuration. Ohmic resistance was not a main factor in performance as this component contributed only 4–7% of the total internal resistance. Transport simulations indicated that hindered oxygen diffusion into the SEA reactor was the primary reason for the increased treatment time. However, a reduction in the overall rate of substrate diffusion also may contribute to the long treatment time with the SEA reactor. These results suggest that SEA designs can more effectively capture energy from wastewater, but SPA configurations will be superior in terms of treatment efficiency due to a greatly reduced time needed for treatment. [Copyright &y& Elsevier]

Abstract: The immense diversity of microbial life found in the vadose zone reflects the extremely heterogeneous and highly dynamic aquatic and chemical environments formed within soil pore spaces. The notion of planktonian free swimming microbes is unrealistic under most unsaturated conditions. Experimental and theoretical evidence suggests that surface attachment is the prevailing lifestyle, where bacterial colonies are embedded in biosynthesized extracellular polymeric substances (EPS). This strategy represents a successful adaptation to the variable and unpredictable hydration conditions near the earth surface. The EPS matrix serves as the interface with the environment; it enhances hydration and transport properties in the immediate vicinity of microbial cells, and dampens effects of highly transient fluctuations in water and nutrient fluxes. The primary effect of soil pore geometry and hydration status is on diffusion pathways to and away from stationary microbial colonies. Microbial dependency on diffusion processes occurs at all scales, but is particularly important at the colony scale. We illustrate the critical role of diffusion pathways with their complex spatial and temporal patterns in promoting coexistence and diversity. We review specific features and adaptations of microbial life to the particular conditions of terrestrial soil environments. The physical and related chemical conditions that shape microbial habitats and govern key processes in unsaturated soils are reviewed in a quantitative framework. Key physiological adaptations and biological responses to challenges presented by unsaturated conditions are discussed. Finally, we discuss potential impacts of microbial activity on properties and characteristics of the host porous medium. This review is an attempt to establish an interdisciplinary dialogue between hydrologists and microbiologists towards a quantitative integration of the role of hydrologic conditions on microbial activity and the role of microbiology in controlling macroscopic fluxes within this important compartment of the biosphere. [Copyright &y& Elsevier]

Microbial carbon-use efficiency (CUE) is defined as the portion of carbon (C) incorporated into biomass relative to the total carbon consumed and plays a pivotal role in regulating microbially-mediated C and nutrient transformations in soil. However, little is understood about how CUE is impacted by edaphic properties, like soil moisture. Soil moisture physically regulates microbial activity through its effects on both water potential and water content. Low water potential can result in high, compensatory intracellular solute concentrations that may inhibit biochemical functions through cytoplasmic desiccation, whereas low soil water content results in thin water films that can limit substrate diffusion, reducing microbial access to dissolved substrates. Because these two aspects of soil moisture may affect microbial respiration differently than C assimilation, they may have different effects on CUE. The purpose of this research was to evaluate the relative importance of water potential and water content in regulating CUE of soil microbial communities. Moist soil incubations of a sandy loam soil were used to determine the impact of both aspects of soil moisture on CUE, and soil slurries were used to determine the impact of water potential alone. Both 13C-acetate and 15N-ammonium were added to moist soils and slurries to quantify gross rates of C and N transformations. In moist soils, acetate assimilation and respiration rates and gross N mineralization and immobilization rates increased exponentially with increasing soil moisture (−3.0 to −0.03 MPa). In contrast, acetate assimilation and respiration and gross N transformation rates remained constant in soil slurries across a similar water potential gradient, created by modifying solute concentrations. Similarly, values of CUE in moist soils increased exponentially with increasing soil moisture, whereas slurry values of CUE remained constant across the soil water potential gradient. Because no changes in rates and CUE were observed in slurries, changes observed in moist soils were attributed to limited substrate diffusion associated with low water contents rather than to adverse physiological effects associated with low water potentials. Results of this study demonstrate that limited substrate diffusion is the primary physical mechanism through which soil moisture regulates microbially-mediated C and N transformation rates and CUE in this sandy loam soil. • Mechanistic effects of soil moisture on CUE evaluated. • Water content regulated CUE in a sandy loam soil. • No effect of water potential per se on CUE in a sandy loam soil. • Water content alone may be a sufficient predictor of microbial activity. [ABSTRACT FROM AUTHOR]

• The chitosan and eggshell membrane powder composite macroparticles were prepared. • The eggshell membrane powder increased the porosity of chitosan macroparticle. • The eggshell membrane powder improved the activity sites for enzyme immobilization. • The increase in pore size could improve the activity of immobilized protease. Chitosan-based macroparticle is a common carrier for enzyme immobilization applied in food industry. Driven by the requirement of large carrier pores for the biomacromolecular substrates such as protein, the eggshell membrane powder (ESMP) was employed as multifunctional porogen to improve the physicochemical structure of chitosan-based macroparticles. The prepared macroparticles were characterized by SEM, XRD, FTIR, Raman spectroscopy, nitrogen adsorption-desorption isotherms, and thermogravimetric analysis. The results showed that an increase of ESMP percentage could improve the porosity of macro holes in macroparticles, and it also enlarged the size of mesopores. Moreover, the ESMP significantly increased (P < 0.05) the amount of papain immobilization, whereas the specific activity of immobilized papain achieved a maximum value of 871.95 U/mg at CSESM2 and then declined with the increase of ESMP. Therefore, the inclusion of 20 % ESMP in chitosan-based macroparticles gave the highest activity of its immobilized protease. [ABSTRACT FROM AUTHOR]

Understanding how the immobilization of enzymes on solid carriers affects their performance is paramount for the design of highly efficient heterogeneous biocatalysts. An efficient supply of substrates onto the solid phase is one of the main challenges to maximize the activity of the immobilized enzymes. Herein, we apply advanced single-particle analysis to decipher the optimal design of an immobilized NADH oxidase (NOX) whose activity depends both on O 2 and NADH concentrations. Carrier physicochemical properties and its functionality along with the enzyme distribution across the carrier were implemented as design variables to study the effects of the intraparticle concentration of substrates (O 2 and NADH) on the activity. Intraparticle O 2 -sensing analysis revealed the superior performance of the enzyme immobilized at the outer surface in terms of effective supply of O 2 . Furthermore, the co-immobilization of NADH and NOX within the tuned surface of porous microbeads increases the effective concentration of NADH in the surroundings of the enzyme. As a result, the optimal spatial organization of NOX and its confinement with NADH allow a 100% recovery of the activity of the soluble enzyme upon the immobilization process. By engineering these variables, we increase the NADH oxidation activity of the heterogeneous biocatalyst by up to 650% compared to NOX immobilized under suboptimal conditions. In conclusion, this work highlights the rational design and engineering of the enzyme-carrier interface to maximize the efficiency of heterogeneous biocatalysts.

Various approaches to magneto-controlled biocatalytic enzyme reactions are discussed with specific example systems. Magnetic nano- and micro-size particles functionalized with enzymes or cofactors/electron transfer mediators have been used to translocate the components of the biocatalytic processes and to activate/inhibit their reactions. Magneto-induced deposition of the functionalized particles on an electrode surface resulted in activation of bioelectrocatalytic reactions. On the other hand, magneto-induced removal of the particles from the electrode surface resulted in the inhibition of the electrochemical reactions. Aggregation/disaggregation of enzyme-modified magnetic nanoparticles resulted in different mechanisms of biocatalytic cascades, changing them reversibly between substrate diffusion and substrate channeling processes. Magnetohydrodynamic activation of bioelectrocatalytic processes allowed enhancement of a biofuel cell operation. Overall, a large variety of possible magneto-controlled enzyme reactions is briefly discussed, particularly emphasizing their applications in different bioelectronic systems., (© 2020 Elsevier Inc. All rights reserved.)