An integrated smartphone-based electrochemical detection system for highly sensitive and on-site detection of chemical oxygen demand by copper-cobalt bimetallic oxide-modified electrode.

A portable and integrated electrochemical detection system has been constructed for on-site and real-time detection of chemical oxygen demand (COD). The system mainly consists of four parts: (i) sensing electrode with a copper-cobalt bimetallic oxide (CuCoOx)-modified screen-printed electrode; (ii) an integrated electrochemical detector for the conversion, amplification, and transmission of weak signals; (iii) a smartphone installed with a self-developed Android application (APP) for issuing commands, receiving, and displaying detection results; and (iv) a 3D-printed microfluidic cell for the continuous input of water samples. Benefiting from the superior catalytic capability of CuCoOx, the developed system shows a high detection sensitivity with 0.335 µA/(mg/L) and a low detection limit of 5.957 mg/L for COD determination and possessing high anti-interference ability to chloride ions. Moreover, this system presents good consistency with the traditional dichromate method in COD detection of actual water samples. Due to the advantages of cost effectiveness, portability, and point-of-care testing, the system shows great potential for water quality monitoring, especially in resource-limited remote areas.

Elemental geochemical evidence for the river-derived sources of trace metals in surface sediments from Hangzhou Bay, East China Sea.

Coastal estuaries are often heavily subject to riverine influences by the inputs of sediment from terrestrial sources. Hangzhou Bay (HZB) is threatened by the riverine derived trace metals from two large rivers of Qiantang River (QTR) and Yangtze River (YZR). However, previous studies mainly focused on the incidental transport from the largest river in China (YZR) and failed to simultaneously evaluate the contributions of these two rivers, especially the directly flowing river of QTR, by their trace elemental geochemical composition and distribution. Herein, a comprehensive study identified the river-derived sources of multiple trace metals in surface sediments which transported from both of the rivers. The sampling stations were separated into three regions of YZR, HZB, and QTR based on their spatial distributions of sediment grain size and components. The significant variations for most of the trace metals concentrations, except for Cd, Th, and U, were found among three regions (χ2 ≥ 8.22, p ≤ 0.016). The highest concentrations in HZB were mainly resulted from the grain size effect (68.82% of the total variance), while the highest concentrations of Sr, Cd, and Ba in YZR and Zr and Hf in QTR were attributed to the anthropogenic source (11.90%) and mineral composition (6.21%) of river basins. After normalized the diversity of multiple trace metals concentrations and the influence of grain size by ratios of Igeo and EFLi, three regions were effectively distinguished. It was indicated that As, Cd, and Sb were enriched in the sediments of rivers by anthropogenic source (EFLi > 1.5 and/or Igeo > 1). The results evidenced that, after removing the influence of grain size, elemental geochemical composition of the surface sediments confidently identified the river-derived anthropogenic sources of the enriched trace metals from two major rivers, and largely from YZR.

Decadal changes of macrofauna community in a semi-enclosed Bay of Yueqing in East China Sea.

To reveal the long-term variation of macrofauna community in Yueqing Bay, an aquacultural bay famous for its shellfish culturing in the East China Sea, macrofauna samples were collected in three period from 2002 to 2003 and 2006-2007 to 2020-2021. The results show that macrofaunal community structure in this area has changed significantly (ANOSIM, p < 0.01) in nearly two decades with significant decreases in species number, biodiversity index and average biomass. Meanwhile, the taxa composition also changed significantly as the dominance of annelid increased while that of mollusks, echinoderms and vertebrates decreased. As a consequence of the variation of taxa composition and total biomass, macrofauna community showed a tendency of miniaturization as individuals with smaller body size and lower biomass dominated the community. According to the results of CCA analysis, temperature, salinity and dissolved oxygen content were the main environmental factors that restricted the species composition of macrofauna community. Further studies still needed to reveal the main reasons that cause the variation of macrofauna community. Overall, the results of this study suggest that the present status of Yueqing Bay benthic ecosystem is concerning from a macrobenthos perspective, as the biodiversity index and biomass of macrofauna decreased significantly. Effective measures should be taken in urgently to restrain the safety and function of coastal ecosystems.

A versatile CuCo@PDA nanozyme-based aptamer-mediated lateral flow assay for highly sensitive, on-site and dual-readout detection of Aflatoxin B1.

Mycotoxin contaminations in food and environment seriously harms human health. Constructing sensitive and point-of-test early-warning tools for mycotoxin determination is in high demand. In this study, a CuCo@PDA nanozyme-based aptamer-mediated lateral flow assay (Apt-LFA) has been elaborately designed for on-site and sensitive determination of mycotoxin Aflatoxin B1 (AFB1). Benefiting from the rich functional groups and excellent peroxidase-like activity, the CuCo@PDA with original dark color can be conjugated with the specific recognition probe (i.e., aptamer), generating colorimetric signal on the test lines of Apt-LFA via a competitive sensing strategy. The signal can further be amplified in-situ by catalytic chromogenic reaction. Therefore, a visual and dual-readout detection of AFB1 has been realized. The developed Apt-LFA provides a flexible detection mode for qualitative and quantitative analysis of AFB1 by naked-eyes observation or smartphone readout. The smartphone-based LFA platform shows a reliable and ultrasensitive determination of AFB1 with the limit of detection (LOD) of 2.2 pg/mL. The recoveries in the real samples are in the range of 95.11-113.77% with coefficients of variations less than 9.84%. This study provides a new approach to realize point-of-test and sensitive detection of mycotoxins in food and environment using nanozyme-based Apt-LFAs.

Coastal eutrophication driven by long-distance transport of large river nutrient loads, the case of Xiangshan Bay, China.

With accelerating anthropogenic activities, the overloading of land-derived nutrients and the resultant eutrophication are threatening coastal aquatic habitats worldwide. In semi-enclosed coastal bays, eutrophication is always considered a local problem that can be mitigated by nutrient reduction at a regional scale. However, as the main nutrient drains major global river discharges can have far-reaching effects over hundreds of kilometers alongshore, which are usually not precisely recognized in local coastal zone management. Here, we first quantified the contributions from both local and remote nutrient sources in Xiangshan Bay (XSB), a eutrophic semi-enclosed bay in China 200 km south of the mouth of the Changjiang River (CJR, the world's third largest river), employing a salinity-based conservative mixing model. We found that the nutrients in Xiangshan Bay were mainly supplied by intruded coastal water fed by CJR discharge, contributing 63 % of dissolved inorganic nitrogen (DIN), 65 % of dissolved silicon (DSi), and 49 % of dissolved inorganic phosphorus (DIP) during the summer of 2017, and 75 % of DIN, 75 % of DSi and 60 % of DIP during the winter of 2019. Additionally, long-term interannual trends in the nutrient concentrations of XSB were generally synchronous with those of the downstream portion of the CJR, indicating that CJR discharge seems to be a strong driver of the eutrophication observed in XSB. In contrast, the impact of local nutrient inputs, such as riverine sewage drainage, aquaculture, biogenic activities, and elemental recycling, was much lower and was regionally limited to the inner bay. Interestingly, the DIP contributions of the local and remote sources were similar, indicating the greater relevance of the internal process. Overall, to mitigate eutrophication in large river-adjacent coastal bays, the inter-regional united practices for nutrient source regulation and ecosystem restoration should be permanently applied along the entire river basin-estuary-coastal continuum.

A highly selective self-powered sensor based on the upconversion nanoparticles/CdS nanospheres for chlorpyrifos detection.

Light sources are crucial for photoelectrochemical (PEC) self-powered sensing, where visible light is widely used. However, due to its high energy, it has some downsides as an irradiation source for overall system, so it is urgent to achieve effective near-infrared (NIR) light absorption because it makes up a significant portion of the solar spectrum. Herein, up-conversion nanoparticles (UCNPs) that could increase the energy of low-energy radiation were combined with semiconductor CdS as the photoactive material (UCNPs/CdS), which broadens the response range of solar spectrum. The NIR light-excited self-powered sensor could be produced via oxidizing H2O at photoanode and lowering dissolved oxygen at cathode under the NIR light without external voltage. Meanwhile, molecularly imprinted polymer (MIP) was added to photoanode as a recognition element to increase the sensor's selectivity. The open-circuit voltage of the self-powered sensor grew linearly as chlorpyrifos concentration climbed from 0.01 to 100 ng mL-1, showing good selectivity as well as reproducibility. This work provides valuable basis for the preparation of efficient and practical PEC sensor with NIR light response.

Hyper-anti-freezing bionic functional surface to -90°C.

Freezing phenomenon has troubled people for centuries, and efforts have been made to lower the liquid freezing temperature, raise the surface temperature, or mechanical deicing. Inspired by the elytra of beetle, we demonstrate a novel functional surface for directional penetration of liquid to reduce icing. The bionic functional surface is fabricated by projection microstereolithography (PµSL) based three dimensional printing technique with the wettability on its two sides tailored by TiO2 nanoparticle sizing agent. A water droplet penetrates from the hydrophobic side to the superhydrophilic side of such a bionic functional surface within 20 ms, but it is blocked in the opposite direction. Most significantly, the penetration time of a water droplet through such a bionic functional surface is much shorter than the freezing time on it, even though the temperature is as low as -90°C. This work opens a gate for the development of functional devices for liquid collection, condensation, especially for hyperantifogging/freezing.

Ecological risk assessment of trace metals in sediments and their effect on benthic organisms from the south coast of Zhejiang province, China.

To explore the ecological risks of trace metals in sediments and their relationship with benthic organisms, 12 trace metals were analyzed and the macrobenthos were identified in the sediments collected from the south coast of Zhejiang province which belongs to the East China Sea. Spatially, the concentrations of most trace metals were high in the estuary, except for Ba and Sr. There was no obvious enrichment for trace metals, except that the concentration of Cd slightly exceeded the coastal background. The ecological risks calculated by the concentrations of Cr, Cd, Cu, Zn, Pb, and Ni in sediments showed that the methods based on sediment quality guidelines could judge the ecological risk more intuitively than the methods based on background value (PN, PLI, RI). The significant correlations between ecological risks and benthos density and biomass revealed the negative impact of trace metals at high concentrations on macrobenthic survival in sediments.

Rapid prototyping enzyme homologs to improve titer of nicotinamide mononucleotide using a strategy combining cell-free protein synthesis with split GFP.

Engineering biological systems to test new pathway variants containing different enzyme homologs is laborious and time-consuming. To tackle this challenge, a strategy was developed for rapidly prototyping enzyme homologs by combining cell-free protein synthesis (CFPS) with split green fluorescent protein (GFP). This strategy featured two main advantages: (1) dozens of enzyme homologs were parallelly produced by CFPS within hours, and (2) the expression level and activity of each homolog was determined simultaneously by using the split GFP assay. As a model, this strategy was applied to optimize a 3-step pathway for nicotinamide mononucleotide (NMN) synthesis. Ten enzyme homologs from different organisms were selected for each step. Here, the most productive homolog of each step was identified within 24 h rather than weeks or months. Finally, the titer of NMN was increased to 1213 mg/L by improving physiochemical conditions, tuning enzyme ratios and cofactor concentrations, and decreasing the feedback inhibition, which was a more than 12-fold improvement over the initial setup. This strategy would provide a promising way to accelerate design-build-test cycles for metabolic engineering to improve the production of desired products.

Influence of biodeposition by suspended cultured oyster on the distributions of trace elements in multiple media in a semi-enclosed bay of China.

It remains unclear how the suspended non-fed bivalve mariculture will alter the coastal transfer and cleaning process of trace elements, the non-degradable contaminants, which have been reported to accumulate in sediment from bivalve mariculture areas. Herein, we set up a field in situ comparative test in the suspended oyster (Crassostrea plicatula) farming area (OF) and reference area (RA) of Xiangshan Bay to verify our hypothesis that the biodepositon of suspended oysters would consolidate trace elements from the water column and transport them to the sediment. Distribution of trace elements in multiple media of biodeposits (BDs), settling particles (SPs), sediments (SEs), and seawater demonstrate that the accelerated deposition of BDs which enriched trace elements from the water column by oysters filtering suspended particles led to trace elements accumulation in SEs from OF. Additionally, As, Cd, Co, Cr, Cu, Ni, V, and Zn were strongly regulated by this process with significant (p < 0.05) higher concentrations in SEs from OF (10.96, 0.20, 13.98, 82.40, 38.47, 38.22, 108.57, and 111.20 µg/g, repectively) than those from RA (9.43, 0.13, 11.76, 63.30, 30.34, 29.55, 86.59, and 100.24 µg/g, repectively), but the extent was different for Mn, Mo, Pb, and W with concentrations in SEs from OF (737.37, 0.81, 30.98, and 3.96 µg/g, repectively) and RA (765.25, 0.69, 31.27, and 3.34 µg/g, repectively), especially for Rb and Sr with concentrations in SEs from OF (131.13 and 96.24 µg/g, repectively) and RA (142.21 and 161.10 µg/g, repectively), due to their geochemical and geophysical properties. Moreover, the harvest of hyper-accumulated oysters as a sink for removing trace elements from water column cannot hide the impact of this process.

3D printed bionic self-powered sensing device based on fern-shaped nitrogen doped BiVO4 photoanode with enriched oxygen vacancies.

A portable three-dimensional (3D) printed bionic sensing device with enhanced photoelectric response was fabricated for sensitive detection of Bisphenol A (BPA). The proposed sensor is operated upon by using a highly reactive dual-electrode system to generate electrical output and provide the sensing signal under photoirradiation, without an external power source. The fern-shaped nitrogen doped BiVO4 photoanode with enriched oxygen vacancies (Ov) bismuth vanadate (N/Ov/BiVO4) photoanode was first synthesized and applied to construct a bionic sensing device. Density functional theoretical (DFT) calculation shows that the synergistic of nitrogen doping and Ov on the surface of photoanode leads to the emergence of impurity levels in BiVO4's electronic structure, promoting the effective separation of photogenerated electron-hole pairs. Impressively, the unique fern-shaped bionic structure enhances the mass transfer efficiency of the sensing system and provides abundant binding sites of aptamer, realizing signal amplification. Moreover, a portable sensing device for automatic sample injection and detection is developed by integrating the detection system into a micromodel based on micro-nano 3D printing technology. Benefit from this ingenious design, the proposed bionic aptasensor displayed excellent electricity output and achieved high sensitivity and selectivity of BPA detection with a low limit of detection (0.025 nM) and broad linear range from 0.1 nM to 100 µM, paving a new way for the development of portable and on-site sensing devices.

Hollow NiCo@C Nanozyme-Embedded Paper-Based Colorimetric Aptasensor for Highly Sensitive Antibiotic Detection on a Smartphone Platform.

Antibiotic residues in the environment and in foods pose a serious threat to ecosystems and human health. Developing sensitive and on-site detection methods is therefore in high demand. In this work, a portable paper-based colorimetric sensor with a smartphone platform with an ultrahigh sensitivity has been designed for on-site and quantitative analysis of antibiotic residues based on aptamer-regulated nanozyme activity. The developed excellent peroxidase-like nanozymes, carbon-protected NiCo bimetal oxides with a unique hollow nanocage structure (NiCo@C HCs), could effectively catalyze the oxidation of chromogenic substrates by H2O2. Once bound to a specific aptamer, the enzyme-mimicking activity of NiCo@C HCs is obviously inhibited as a result of the masking of active sites but could be restored via the target-aptamer recognition. Herein, the aptamer-modified NiCo@C HCs are embedded on paper pieces to construct paper-based biochips for visual detection. Meanwhile, a smartphone platform is integrated for the signal readout. Using enrofloxacin (ENR) as an analyte model, the proposed paper-based analysis platform shows a reliable and sensitive detection of ENR with an ultralow detection limit of 0.029 ng/mL. The platform also works well in various real samples. This analysis method is facile in design, showing a great application potential for on-site and mass screening of antibiotic residues in the environment and in foods.

Multifunctional MnCo@C yolk-shell nanozymes with smartphone platform for rapid colorimetric analysis of total antioxidant capacity and phenolic compounds.

Accurate on-site analysis of food quality, environmental pollutants, and disease biomarkers is of great significance for safeguarding public health. In this work, based on the novel nanozymes, MnCo oxides@carbon yolk-shell nanocages (MnCo@C NCs), a portable colorimetric sensor with smartphone platform has been developed for rapid, on-site and quantitative analysis of total antioxidant capacity (TAC) and phenolic compounds. The MnCo@C NCs are synthesized via one-step calcination of polydopamine-coated MnCo Prussian blue analogs (MnCo-PBA@PDA). The PDA-derived carbon shell is found to be able to protect the nanocages from collapsing, thus increasing their specific surface areas and porosity. Benefiting from the unique structure and multivalent MnCo bimetallic oxides, the MnCo@C NCs perform outstanding catalytic performance and multiple enzyme-mimicking activities including oxidase, laccase and catalase. Hence, a multifunctional application platform integrated smartphone has been constructed for rapid and sensitive colorimetric detection of three model analytes (i.e., ascorbic acid (AA), 2,4-dichlorophenol (2,4-DP), and epinephrine) with extremely low detection limits of 0.29 µM, 0.76 µM, and 0.70 µM, respectively. This sensor device is successfully applied in TAC analysis in vegetables, fruits, and beverages, as well as epinephrine determination in human serum samples. This work provides new insights into designing multifunctional nanozymes to advance the instant detection technology in the field of food supervision, environment monitoring, and human health.

A flexible photoelectrochemical aptasensor using heterojunction architecture of α-Fe2O3/d-C3N4 for ultrasensitive detection of penbritin.

The performance of photoelectrochemical (PEC) analysis system relies closely on the properties of the photoelectric electrodes. It is of great significance to integrate photoactive materials with flexible substrates to construct ultra-sensitive PEC sensors for practical application. This work reports a novel photoelectrode developed by immobilizing α-Fe2O3 nanoparticles (NPs)/defect-rich carbon nitride (d-C3N4), an excellent Z-scheme heterojunction photoelectric material, onto three-dimensional (3D) flexible carbon fiber textile. Specifically, 3D hierarchical structure of flexible carbon fiber textile provides larger specific surface area and higher mechanical strength than traditional electrodes, resulting in more reaction sites and faster reaction kinetics to achieve signal amplification. Simultaneously, α-Fe2O3/d-C3N4 Z-scheme heterojunction exhibits enhanced light absorption capability and high redox ability, thus dramatically improving the PEC performance. This photoelectrode was used to construct a flexible PEC aptasensor for ultrasensitive detection of penbritin, demonstrating excellent performance in terms of wide linear range (0.5 pM-50 nM), low detection limit (0.0125 pM) and high stability. The design principle is applicable to the manufacture of other photoelectric sensing systems, which provides an avenue for the development of portable environmental analysis and field diagnostics equipment.

3D-Printed Complex Microstructures with a Self-Sacrificial Structure Enabled by Grayscale Polymerization and Ultrasonic Treatment.

Complex three-dimensional (3D) microstructures are attracting more and more attention in many applications such as microelectromechanical systems, biomedical engineering, new materials, new energy, environmental protection, and wearable electronics. However, fabricating complex 3D microstructures by 3D printing techniques, especially those with long suspended structures, needs to introduce additional supporting structures, which are difficult to be removed. Here, we propose a simple method in which the supporting structures can be easily removed by optimizing their size and the grayscale value working with ultrasonic treatment in ethanol solution. The 3D microstructures and the supporting structures made of the same insoluble materials are fabricated simultaneously by using a projection microstereolithography system with a dynamic mask. The results demonstrate that the supporting structures play a key role in the fabrication of the long suspended structures while they can be easily removed. The removal time decreases with the increase in the height of the supporting microstructures, and the breaking force and shearing force of the supporting structures increase with the increase in their grayscale and the diameter. In addition, theory and the multiphysics simulation validate that the stress concentration at the top and the bottom of the supporting structures due to the cavitation from ultrasonic vibration dominates the removal of the supporting structures. Finally, a tree-like structure is precisely fabricated by using our method. The present study provides a new way for the removal of the supporting structures for 3D printed suspended microstructures.

Heavy metal concentrations in tissues of marine fish and crab collected from the middle coast of Zhejiang Province, China.

Concentrations of the heavy metals As, Cd, Cu, Hg, Pb, and Zn in various tissues of five marine fish species and one crab species collected from the middle coast of Zhejiang Province of China were investigated in this study. The results indicated considerable variation in heavy metal concentrations in different tissues and species. Elevated concentrations of most heavy metals were identified in fish gills and crab gills and hepatopancreas, with some differences by heavy metal type. In addition, carnivorous and benthivorous fish species generally contained relatively high concentrations of heavy metals due to feeding habits and habitats. Geographical variations of heavy metal concentrations in muscle may be attributable to species-dependent differences and terrigenous contamination. The potential health risk assessment suggested that exposure doses of most heavy metals were safe for human consumption, with the exception of As.

Kelp cultivation effectively improves water quality and regulates phytoplankton community in a turbid, highly eutrophic bay.

Coastal eutrophication and its associated harmful algal blooms have emerged as one of the most severe environmental problems worldwide. Seaweed cultivation has been widely encouraged to control eutrophication and algal blooms. Among them, cultivated kelp (Saccharina japonica) dominates primarily by production and area. However, the responses of water quality and phytoplankton community to kelp farming remain unclear. Here, thirteen cruises were conducted in the kelp farms and control areas in the turbid, highly eutrophic Xiangshan Bay of the East China Sea from 2008 to 2015. Results indicated that kelp cultivation slightly increased dissolved oxygen and pH, but reduced dissolved inorganic nitrogen and phosphorus. We estimated that kelp harvesting would remove 297 t of nitrogen and 42 t of phosphorus from this bay annually. Because of decreased flow velocity, turbulence, and sediment resuspension, kelp farming greatly reduced suspended solids and increased transparency, resulting in increases in phytoplankton chlorophyll a and abundance. Additionally, kelp farming appreciably increased phytoplankton species number, Marglef richness, and Shannon-Wiener diversity indices by 51.6%, 40.1%, and 13.1%, respectively. Analysis of similarity and similarity percentages demonstrated that phytoplankton community composition differed significantly between the farm and control area, which was mostly attributed to long-chained diatoms and single-celled dinoflagellates. However, after the kelp harvesting, all measurements of water quality and phytoplankton biomass, diversity, and community composition exhibited no significant difference. Our study highlights that kelp cultivation alleviates eutrophication and acidification and enhances phytoplankton diversity, thus providing guidance for macroalgal aquaculture and remediation in eutrophic waters.

Effects of fish cage culture and suspended oyster culture on macrobenthic communities in Xiangshan Bay, a semi-enclosed subtropical bay in eastern China.

The impacts of fish cage culture and suspended oyster culture on macrobenthic communities were investigated in Xiangshan Bay, China, on a seasonal basis from January to October of 2015. Samples were collected from a fish cage farm, a suspended oyster farm, and two corresponding reference sites. Two-way ANOVA results showed that species richness, abundance, biomass, and Shannon-Wiener diversity differed significantly between the four different investigated areas, and different seasons as well. Cluster analysis showed that macrobenthic community composition in the fish and oyster culture areas significantly differed from that in the reference sites, respectively. Trophic structure of macrobenthos in the fish and oyster culture areas mostly clustered together owing to higher abundance and biomass of surface-deposit feeders and carnivores. The macrobenthic communities and feeding guilds correlated highly with environmental factors, such as bottom water chlorophyll a and nutrients, as well as sediment total organic carbon. Although integrated multi-trophic aquaculture is regarded as a suitable approach to coordinate desirable economic, social, and environmentally sustainable outcomes, coastal ecosystems may suffer from large-scale nutrient enrichment due to aquaculture and other human activities, which should not be considered in isolation.

Oyster farming control on phytoplankton bloom promoted by thermal discharge from a power plant in a eutrophic, semi-enclosed bay.

Temperature increase caused by thermal discharge from power plants promotes phytoplankton growth and frequent bloom in eutrophic subtropical waters, particularly in cold seasons. Suspension filter-feeding bivalves show size-selective grazing on phytoplankton. Thus, we hypothesized that algal bloom under thermal stimulation could be controlled and that phytoplankton community was structured by oyster farming. Here, ten cruises were conducted in two oyster farms (OFs) and control areas (CAs) adjacent to the Ninghai Power Plant in the upper section of Xiangshan Bay during 2009-2015. We found that thermal discharge induced severe winter algal blooms. Phytoplankton abundance and chlorophyll a (chla) were significantly lower (46.3% and 28.3%, respectively) in OF than in CA, indicating a high filtration efficiency by oysters and the associated biofouling assemblages. In addition, oyster farming significantly increased species richness (by 26.3%), Shannon-Wiener diversity (by 38.3%), and Pielou's evenness indices (by 28.8%) and reduced suspended solids (by 12.2%), total organic carbon (by 18.4%), dissolved inorganic nitrogen (by 1.5%), and phosphorus (by 3.7%). Furthermore, oyster farming considerably reduced (increased) micro-chla contribution (pheophytin/chla) by 34.8% (71.1%), suggesting a strong size-selective grazing on phytoplankton. Analysis of similarity revealed a significant difference in phytoplankton community composition between OF and CA. However, after the removal of culture rafts, all the abundance, chla, species diversity, dominant species, size structure, and community composition of phytoplankton showed no significant difference. Our study demonstrated that oyster farming effectively alleviated eutrophication and algal bloom and enhanced phytoplankton diversity, which provides guidance for aquaculture and ecological restoration in subtropical coastal eutrophic waters.

Improved Efficiency of the Desulfurization of Oil Sulfur Compounds in Escherichia coli Using a Combination of Desensitization Engineering and DszC Overexpression.

The 4S pathway of biodesulfurization, which can specifically desulfurize aromatic S-heterocyclic compounds without destroying their combustion value, is a low-cost and environmentally friendly technology that is complementary to hydrodesulfurization. The four Dsz enzymes convert the model compound dibenzothiophene (DBT) into the sulfur-free compound 2-hydroxybiphenyl (HBP). Of these four enzymes, DszC, the first enzyme in the 4S pathway, is the most severely affected by the feedback inhibition caused by HBP. This study is the first attempt to directly modify DszC to decrease its inhibition by HBP, with the results showing that the modified protein is insensitive to HBP. On the basis of the principle that the final HBP product could show a blue color with Gibbs reagent, a high-throughput screening method for its rapid detection was established. The screening method and the combinatorial mutagenesis generated the mutant AKWC (A101K/W327C) of DszC. After the IC50 was calculated, the feedback inhibition of the AKWC mutant was observed to have been substantially reduced. Interestingly, the substrate inhibition of DszC had also been reduced as a result of directed evolution. Finally, the recombinant BL21(DE3)/BADC*+C* (C* represents AKWC) strain exhibited a specific conversion rate of 214.84 µmolHBP/gDCW/h, which was 13.8-fold greater than that of the wild-type strain. Desensitization engineering and the overexpression of the desensitized DszC protein resulted in the elimination of the feedback inhibition bottleneck in the 4S pathway, which is practical and effective progress toward the production of sulfur-free fuel oil. The results of this study demonstrate the utility of desensitization of feedback inhibition regulation in metabolic pathways by protein engineering.