Isolation and characterization of pure cultures for metabolizing 1,4-dioxane in oligotrophic environments.

1,4-Dioxane concentration in most contaminated water is much less than 1 mg/L, which cannot sustain the growth of most reported 1,4-dioxane-metabolizing pure cultures. These pure cultures were isolated following enrichment of mixed cultures at high concentrations (20 to 1,000 mg/L). This study is based on a different strategy: 1,4-dioxane-metabolizing mixed cultures were enriched by periodically spiking 1,4-dioxane at low concentrations (≤1 mg/L). Five 1,4-dioxane-metabolizing pure strains LCD6B, LCD6D, WC10G, WCD6H, and WD4H were isolated and characterized. The partial 16S rRNA gene sequencing showed that the five bacterial strains were related to Dokdonella sp. (98.3%), Acinetobacter sp. (99.0%), Afipia sp. (99.2%), Nitrobacter sp. (97.9%), and Pseudonocardia sp. (99.4%), respectively. Nitrobacter sp. WCD6H is the first reported 1,4-dioxane-metabolizing bacterium in the genus of Nitrobacter. The net specific growth rates of these five cultures are consistently higher than those reported in the literature at 1,4-dioxane concentrations <0.5 mg/L. Compared to the literature, our newly discovered strains have lower half-maximum-rate concentrations (1.8 to 8.2 mg-dioxane/L), lower maximum specific 1,4-dioxane utilization rates (0.24 to 0.47 mg-dioxane/(mg-protein ⋅ d)), higher biomass yields (0.29 to 0.38 mg-protein/mg-dioxane), and lower decay coefficients (0.01 to 0.02 d-1). These are characteristics of microorganisms living in oligotrophic environments.

Photosynthetic biohybrid coculture for tandem and tunable CO2 and N2 fixation.

Solar-driven bioelectrosynthesis represents a promising approach for converting abundant resources into value-added chemicals with renewable energy. Microorganisms powered by electrochemical reducing equivalents assimilate CO2, H2O, and N2 building blocks. However, products from autotrophic whole-cell biocatalysts are limited. Furthermore, biocatalysts tasked with N2 reduction are constrained by simultaneous energy-intensive autotrophy. To overcome these challenges, we designed a biohybrid coculture for tandem and tunable CO2 and N2 fixation to value-added products, allowing the different species to distribute bioconversion steps and reduce the individual metabolic burden. This consortium involves acetogen Sporomusa ovata, which reduces CO2 to acetate, and diazotrophic Rhodopseudomonas palustris, which uses the acetate both to fuel N2 fixation and for the generation of a biopolyester. We demonstrate that the coculture platform provides a robust ecosystem for continuous CO2 and N2 fixation, and its outputs are directed by substrate gas composition. Moreover, we show the ability to support the coculture on a high-surface area silicon nanowire cathodic platform. The biohybrid coculture achieved peak faradaic efficiencies of 100, 19.1, and 6.3% for acetate, nitrogen in biomass, and ammonia, respectively, while maintaining product tunability. Finally, we established full solar to chemical conversion driven by a photovoltaic device, resulting in solar to chemical efficiencies of 1.78, 0.51, and 0.08% for acetate, nitrogenous biomass, and ammonia, correspondingly. Ultimately, our work demonstrates the ability to employ and electrochemically manipulate bacterial communities on demand to expand the suite of CO2 and N2 bioelectrosynthesis products.

Enhancing Biohybrid CO2 to Multicarbon Reduction via Adapted Whole-Cell Catalysts.

Catalytic CO2 conversion to renewable fuel is of utmost importance to establish a carbon-neutral society. Bioelectrochemical CO2 reduction, in which a solid cathode interfaces with CO2-reducing bacteria, represents a promising approach for renewable and sustainable fuel production. The rational design of biocatalysts in the biohybrid system is imperative to effectively reduce CO2 into valuable chemicals. Here, we introduce methanol adapted Sporomusa ovata (S. ovata) to enhance the slow metabolic activity of wild-type microorganisms to our semiconductive silicon nanowires (Si NWs) array for efficient CO2 reduction. The adapted whole-cell catalysts enable an enhancement of CO2 fixation with a superior faradaic efficiency on the poised Si NWs cathode. The synergy of the high-surface-area cathode and the adapted strain achieves a CO2-reducing current density of 0.88 ± 0.11 mA/cm2, which is 2.4-fold higher than the wild-type strain. This new generation of biohybrids using adapted S. ovata also decreases the charge transfer resistance at the cathodic interface and facilitates the faster charge transfer from the solid electrode to bacteria.

Interaction between humic acid and silica in reverse osmosis membrane fouling process: A spectroscopic and molecular dynamics insight.

Combined organic and inorganic fouling is a primary barrier constraining the performance of reverse osmosis (RO) membrane. In this work, we conducted a systematic study focusing on the synergetic fouling effects of silica and humic acid (HA) in RO process, and found the critical silica concentration where the fouling pattern changed qualitatively. When the silica concentration was lower than 6 mM at a typical HA concentration of 50 mg·L-1, no severe fouling was observed, while silica reaching this critical point could cause severe synergetic fouling with HA. Concentrated silica above the critical point acted as the prior foulant with marginal fouling effect caused by HA. A variety of solutions and surface-based characterizations were performed to elucidate the synergistic fouling responsibility for silica and HA. Our study suggests that the carboxylic groups from HA formed hydrogen bonds with silica hydrate, inducing silica adsorption onto HA aggregates at low silica particle concentrations. The HA network was bridged together to form large foulants due to the silica-silica interaction above the silica critical concentration. These mechanisms were further confirmed by molecular dynamics simulations. This study provides an in-depth insight into the combined organic-inorganic fouling and can serve as a guideline to optimize feed conditions in order to mitigate fouling of RO in wastewater reusing industry.

Rapid fabrication of precise high-throughput filters from membrane protein nanosheets.

Biological membranes are ideal for separations as they provide high permeability while maintaining high solute selectivity due to the presence of specialized membrane protein (MP) channels. However, successful integration of MPs into manufactured membranes has remained a significant challenge. Here, we demonstrate a two-hour organic solvent method to develop 2D crystals and nanosheets of highly packed pore-forming MPs in block copolymers (BCPs). We then integrate these hybrid materials into scalable MP-BCP biomimetic membranes. These MP-BCP nanosheet membranes maintain the molecular selectivity of the three types of ß-barrel MP channels used, with pore sizes of 0.8 nm, 1.3 nm, and 1.5 nm. These biomimetic membranes demonstrate water permeability that is 20-1,000 times greater than that of commercial membranes and 1.5-45 times greater than that of the latest research membranes with comparable molecular exclusion ratings. This approach could provide high performance alternatives in the challenging sub-nanometre to few-nanometre size range.

Author Correction: Artificial water channels enable fast and selective water permeation through water-wire networks.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Artificial water channels enable fast and selective water permeation through water-wire networks.

Artificial water channels are synthetic molecules that aim to mimic the structural and functional features of biological water channels (aquaporins). Here we report on a cluster-forming organic nanoarchitecture, peptide-appended hybrid[4]arene (PAH[4]), as a new class of artificial water channels. Fluorescence experiments and simulations demonstrated that PAH[4]s can form, through lateral diffusion, clusters in lipid membranes that provide synergistic membrane-spanning paths for a rapid and selective water permeation through water-wire networks. Quantitative transport studies revealed that PAH[4]s can transport >109 water molecules per second per molecule, which is comparable to aquaporin water channels. The performance of these channels exceeds the upper bound limit of current desalination membranes by a factor of ~104, as illustrated by the water/NaCl permeability-selectivity trade-off curve. PAH[4]'s unique properties of a high water/solute permselectivity via cooperative water-wire formation could usher in an alternative design paradigm for permeable membrane materials in separations, energy production and barrier applications.

Electron tomography reveals details of the internal microstructure of desalination membranes.

As water availability becomes a growing challenge in various regions throughout the world, desalination and wastewater reclamation through technologies such as reverse osmosis (RO) are becoming more important. Nevertheless, many open questions remain regarding the internal structure of thin-film composite RO membranes. In this work, fully aromatic polyamide films that serve as the active layer of state-of-the-art water filtration membranes were investigated using high-angle annular dark-field scanning transmission electron microscopy tomography. Reconstructions of the 3D morphology reveal intricate aspects of the complex microstructure not visible from 2D projections. We find that internal voids of the active layer of compressed commercial membranes account for less than 0.2% of the total polymer volume, contrary to previously reported values that are two orders of magnitude higher. Measurements of the local variation in polyamide density from electron tomography reveal that the polymer density is highest at the permeable surface for the two membranes tested and establish the significance of surface area on RO membrane transport properties. The same type of analyses could provide explanations for different flux variations with surface area for other types of membranes where the density is distributed differently. Thus, 3D reconstructions and quantitative analyses will be crucial to characterize the complex morphology of polymeric membranes used in next-generation water-purification membranes.

Publisher Correction: Achieving high permeability and enhanced selectivity for Angstrom-scale separations using artificial water channel membranes.

The original version of this Article contained an error in the spelling of the author Woochul Song, which was incorrectly given as Woochul C. Song. This has been corrected in both the PDF and HTML versions of the Article.

Creating cross-linked lamellar block copolymer supporting layers for biomimetic membranes.

The long-standing goal in membrane development is creating materials with superior transport properties, including both high flux and high selectivity. These properties are common in biological membranes, and thus mimicking nature is a promising strategy towards improved membrane design. In previous studies, we have shown that artificial water channels can have excellent water transport abilities that are comparable to biological water channel proteins, aquaporins. In this study, we propose a strategy for incorporation of artificial channels that mimic biological channels into stable polymeric membranes. Specifically, we synthesized an amphiphilic triblock copolymer, poly(isoprene)-block-poly(ethylene oxide)-block-poly(isoprene), which is a high molecular weight synthetic analog of naturally occurring lipids in terms of its self-assembled structure. This polymer was used to build stacked membranes composed of self-assembled lamellae. The resulting membranes resemble layers of natural lipid bilayers in living systems, but with superior mechanical properties suitable for real-world applications. The procedures used to synthesize the triblock copolymer resulted in membranes with increased stability due to the crosslinkability of the hydrophobic domains. Furthermore, the introduction of bridging hydrophilic domains leads to the preservation of the stacked membrane structure when the membrane is in contact with water, something that is challenging for diblock lamellae that tend to swell, and delaminate in aqueous solutions. This new method of membrane fabrication offers a practical model for making channel-based biomimetic membranes, which may lead to technological applications in reverse osmosis, nanofiltration, and ultrafiltration membranes.

Unique selectivity trends of highly permeable PAP[5] water channel membranes.

Artificial water channels are a practical alternative to biological water channels for achieving exceptional water permeability and selectivity in a stable and scalable architecture. However, channel-based membrane fabrication faces critical barriers such as: (1) increasing pore density to achieve measurable gains in permeability while maintaining selectivity, and (2) scale-up to practical membrane sizes for applications. Recently, we proposed a technique to prepare channel-based membranes using peptide-appended pillar[5]arene (PAP[5]) artificial water channels, addressing the above challenges. These multi-layered PAP[5] membranes (ML-PAP[5]) showed significantly improved water permeability compared to commercial membranes with similar molecular weight cut-offs. However, due to the distinctive pore structure of water channels and the layer-by-layer architecture of the membrane, the separation behavior is unique and was still not fully understood. In this paper, two unique selectivity trends of ML-PAP[5] membranes are discussed from the perspectives of channel geometry, ion exclusion, and linear molecule transport.

Achieving high permeability and enhanced selectivity for Angstrom-scale separations using artificial water channel membranes.

Synthetic polymer membranes, critical to diverse energy-efficient separations, are subject to permeability-selectivity trade-offs that decrease their overall efficacy. These trade-offs are due to structural variations (e.g., broad pore size distributions) in both nonporous membranes used for Angstrom-scale separations and porous membranes used for nano to micron-scale separations. Biological membranes utilize well-defined Angstrom-scale pores to provide exceptional transport properties and can be used as inspiration to overcome this trade-off. Here, we present a comprehensive demonstration of such a bioinspired approach based on pillar[5]arene artificial water channels, resulting in artificial water channel-based block copolymer membranes. These membranes have a sharp selectivity profile with a molecular weight cutoff of ~ 500 Da, a size range challenging to achieve with current membranes, while achieving a large improvement in permeability (~65 L m-2 h-1 bar-1 compared with 4-7 L m-2 h-1 bar-1) over similarly rated commercial membranes.

Multiple antibiotic resistance genes distribution in ten large-scale membrane bioreactors for municipal wastewater treatment.

Wastewater treatment plants are thought to be potential reservoirs of antibiotic resistance genes. In this study, GeoChip was used for analyzing multiple antibiotic resistance genes, including four multidrug efflux system gene groups and three ß-lactamase genes in ten large-scale membrane bioreactors (MBRs) for municipal wastewater treatment. Results revealed that the diversity of antibiotic genes varied a lot among MBRs, but about 40% common antibiotic resistance genes were existent. The average signal intensity of each antibiotic resistance group was similar among MBRs, nevertheless the total abundance of each group varied remarkably and the dominant resistance gene groups were different in individual MBR. The antibiotic resistance genes majorly derived from Proteobacteria and Actinobacteria. Further study indicated that TN, TP and COD of influent, temperature and conductivity of mixed liquor were significant (P<0.05) correlated to the multiple antibiotic resistance genes distribution in MBRs.

Salt-Excluding Artificial Water Channels Exhibiting Enhanced Dipolar Water and Proton Translocation.

Aquaporins (AQPs) are biological water channels known for fast water transport (∼10(8)-10(9) molecules/s/channel) with ion exclusion. Few synthetic channels have been designed to mimic this high water permeability, and none reject ions at a significant level. Selective water translocation has previously been shown to depend on water-wires spanning the AQP pore that reverse their orientation, combined with correlated channel motions. No quantitative correlation between the dipolar orientation of the water-wires and their effects on water and proton translocation has been reported. Here, we use complementary X-ray structural data, bilayer transport experiments, and molecular dynamics (MD) simulations to gain key insights and quantify transport. We report artificial imidazole-quartet water channels with 2.6 Špores, similar to AQP channels, that encapsulate oriented dipolar water-wires in a confined chiral conduit. These channels are able to transport ∼10(6) water molecules/s, which is within 2 orders of magnitude of AQPs' rates, and reject all ions except protons. The proton conductance is high (∼5 H(+)/s/channel) and approximately half that of the M2 proton channel at neutral pH. Chirality is a key feature influencing channel efficiency.

Highly permeable artificial water channels that can self-assemble into two-dimensional arrays.

Bioinspired artificial water channels aim to combine the high permeability and selectivity of biological aquaporin (AQP) water channels with chemical stability. Here, we carefully characterized a class of artificial water channels, peptide-appended pillar[5]arenes (PAPs). The average single-channel osmotic water permeability for PAPs is 1.0(± 0.3) × 10(-14) cm(3)/s or 3.5(± 1.0) × 10(8) water molecules per s, which is in the range of AQPs (3.4 ∼ 40.3 × 10(8) water molecules per s) and their current synthetic analogs, carbon nanotubes (CNTs, 9.0 × 10(8) water molecules per s). This permeability is an order of magnitude higher than first-generation artificial water channels (20 to ∼ 10(7) water molecules per s). Furthermore, within lipid bilayers, PAP channels can self-assemble into 2D arrays. Relevant to permeable membrane design, the pore density of PAP channel arrays (∼ 2.6 × 10(5) pores per µm(2)) is two orders of magnitude higher than that of CNT membranes (0.1 ∼ 2.5 × 10(3) pores per µm(2)). PAP channels thus combine the advantages of biological channels and CNTs and improve upon them through their relatively simple synthesis, chemical stability, and propensity to form arrays.

Linkages between microbial functional potential and wastewater constituents in large-scale membrane bioreactors for municipal wastewater treatment.

Large-scale membrane bioreactors (MBRs) have been widely used for the municipal wastewater treatment, whose performance relies on microbial communities of activated sludge. Nevertheless, microbial functional structures in MBRs remain little understood. To gain insight into functional genes and their steering environmental factors, we adopted GeoChip, a high-throughput microarray-based tool, to examine microbial genes in four large-scale, in-operation MBRs located in Beijing, China. The results revealed substantial microbial gene heterogeneity (43.7-85.1% overlaps) among different MBRs. Mantel tests indicated that microbial nutrient cycling genes were significantly (P < 0.05) correlated to influent COD, [Formula: see text] -N, TP or sulfate, which signified the importance of microbial mediation of wastewater constituent removal. In addition, functional genes shared by all four MBRs contained a large number of genes involved in antibiotics resistance, metal resistance and organic remediation, suggesting that they were required for degradation or resistance to toxic compounds in wastewater. The linkages between microbial functional structures and environmental variables were also unveiled by the finding of hydraulic retention time, influent COD, [Formula: see text] -N, mixed liquid temperature and humic substances as major factors shaping microbial communities. Together, the results presented demonstrate the utility of GeoChip-based microarray approach in examining microbial communities of wastewater treatment plants and provide insights into the forces driving important processes of element cycling.

Molecular cloning, overexpression and characterization of a novel water channel protein from Rhodobacter sphaeroides.

Aquaporins are highly selective water channel proteins integrated into plasma membranes of single cell organisms; plant roots and stromae; eye lenses, renal and red blood cells in vertebrates. To date, only a few microbial aquaporins have been characterized and their physiological importance is not well understood. Here we report on the cloning, expression and characterization of a novel aquaporin, RsAqpZ, from a purple photosynthetic bacterium, Rhodobacter sphaeroides ATCC 17023. The protein was expressed homologously at a high yield (∼20 mg/L culture) under anaerobic photoheterotrophic growth conditions. Stopped-flow light scattering experiments demonstrated its high water permeability (0.17±0.05 cm/s) and low energy of activation for water transport (2.93±0.60 kcal/mol) in reconstituted proteoliposomes at a protein to lipid ratio (w/w) of 0.04. We developed a fluorescence correlation spectroscopy based technique and utilized a fluorescent protein fusion of RsAqpZ, to estimate the single channel water permeability of RsAqpZ as 1.24 (±0.41) x 10(-12) cm(3)/s or 4.17 (±1.38)×10(10) H2O molecules/s, which is among the highest single channel permeability reported for aquaporins. Towards application to water purification technologies, we also demonstrated functional incorporation of RsAqpZ in amphiphilic block copolymer membranes.

Improvement on the modified Lowry method against interference of divalent cations in soluble protein measurement.

This paper systematically investigated the interference of calcium and magnesium in protein measurement with a modified Lowry method first proposed by Frølund et al. (Appl Microbiol Biotechnol 43:755-761, 1995). This interference has in the past been largely ignored resulting in variable and unreliable results when applied to natural water matrices. We discovered significant formation of calcium and magnesium precipitates that lead to a decline in light absorbance at 750 nm during protein determination. Underestimation of protein concentration (sometimes even yielding negative concentrations) and low experiment reproducibility were demonstrated at high concentrations of divalent cations (e.g., [Ca(2+)] over 1 mmol L(-1)). To eliminate interference from calcium and magnesium, two pretreatment strategies were established based on cation exchange and dialysis. These pretreatments were convenient and were found to be highly effective in removing calcium and magnesium in protein samples. By using the modified Lowry method with these pretreatments, proteins in standard solutions and in wastewater samples were successfully quantified with good reliability and reproducibility. In addition, we demonstrated that simultaneous quantification of humic substances with the modified Lowry method was not affected by the two pretreatments. These approaches are expected to be applicable to protein and humic substance determination in different research fields, in cases where the modified Lowry method is sensitive to divalent cation concentrations.

High-density reconstitution of functional water channels into vesicular and planar block copolymer membranes.

The exquisite selectivity and unique transport properties of membrane proteins can be harnessed for a variety of engineering and biomedical applications if suitable membranes can be produced. Amphiphilic block copolymers (BCPs), developed as stable lipid analogs, form membranes that functionally incorporate membrane proteins and are ideal for such applications. While high protein density and planar membrane morphology are most desirable, BCP-membrane protein aggregates have so far been limited to low protein densities in either vesicular or bilayer morphologies. Here, we used dialysis to reproducibly form planar and vesicular BCP membranes with a high density of reconstituted aquaporin-0 (AQP0) water channels. We show that AQP0 retains its biological activity when incorporated at high density in BCP membranes, and that the morphology of the BCP-protein aggregates can be controlled by adjusting the amount of incorporated AQP0. We also show that BCPs can be used to form two-dimensional crystals of AQP0.

Fouling characteristics in a membrane bioreactor coupled with anaerobic-anoxic-oxic process for coke wastewater treatment.

Experiments were conducted to investigate the fouling characteristics of a membrane bioreactor combined with anaerobic-anoxic-oxic process for coke wastewater treatment. Supernatant from the oxic tank was characterized as different hydrophilic/hydrophobic fractions by DAX-8 resin, with joint size partition also undertaken. Polysaccharides and proteins, mainly the fraction with molecular weight above 100kDa, were liable to accumulate in the supernatant. Hydrophilic fraction, mainly contributing to the subclass of molecular weight above 100kDa, was found most likely responsible for the flux deterioration by means of dead-end filtration tests. Analyses of particle and membrane pore size distribution revealed that major foulants had size comparable to the pore diameter. It can be inferred that steric factor (i.e. size exclusion) behaved primarily in the initial stage of fouling, while the role of hydrophobic interaction was of less significance.