N-containing dissolved organic matter promotes dissolved inorganic carbon supersaturation in the Yangtze River, China.

Dissolved inorganic carbon (DIC) represents a major global carbon pool and the flux from rivers to oceans has been observed to be increasing. The effect of weathering with respect to increasing DIC has been widely studied in recent decades; however, the influence of dissolved organic matter (DOM) on increasing DIC in large rivers remains unclear. This study employed stable carbon isotopes and Fourier transform ion cyclotron mass spectrometry (FT-ICR MS) to investigate the effect of the molecular composition of DOM on the DIC in the Yangtze River. The results showed that organic matter is an important source of DIC in the Yangtze River, accounting for 40.0 ± 12.1 % and 32.0 ± 7.2 % of DIC in wet and dry seasons, respectively, and increased along the river by approximately three times. Nitrogen (N)-containing DOM, an important composition in DOM with a percentage of ∼40 %, showed superior oxidation state than non N-containing DOM, suggesting that the presence of N could improve the degradable potential of DOM. Positive relationship between organic sourced DIC (DICOC) and N-containing DOM formulae indicated that N-containing DOM is crucial to facilitate the mineralization of DOM to DICOC. N-containg molecular formular with low H/C and O/C ratio were positively correlated with DICOC further verified these energy-rich and biolabile compounds are preferentially decomposed by bacteria to produce DIC. N-containing components significantly accelerated the degradation of DOM to DICOC, which is important for understanding the CO2 emission and carbon cycling in large rivers.

Short-term photodegradation of autochthonous and allochthonous dissolved organic matter in Lake Taihu, China.

Photochemistry is one of the key processes that shape the quality of dissolved organic matter (DOM) in aquatic systems, yet the photoreactivity of DOM from different sources remains largely unclear. In this study, DOM from 10 typical autochthonous and allochthonous sources in Lake Taihu basin were exposed to simulated sunlight, and quantitative and compositional changes of the DOM were explored by measuring its UV-Visable absorption and fluorescence spectroscopy. Photochemical release of nutrients was also explored during the incubations. Results showed that, although DOM from most sources experienced photobleaching effects with decreased absorption coefficients at 254 nm (a(254)) and fluorescence component intensities after light exposure, photochemical alterations of DOM linked to their original composition. Macrophyte-derived (Potamogeton malaianus) DOM, with the largest molecular size, showed increased a(254), humic- and protein-like fluorescence component (C1 and C2) abundances, and inorganic nutrient concentrations relative to dark controls, indicating photo-release of labile components. However, DOM with relatively higher aromaticity, e.g., from agricultural water and the lake, showed photobleaching effects and increased humification degree, probably due to the loss of aromatic components. Allochthonous anthropogenic DOM, e.g., from sewage, showed stronger photo-ammonification, likely relating to the fresh labile N-containing compositions. The form of inorganic nutrient releases during the DOM photolysis also varied with the original DOM sources. Macrophyte-derived DOM incubations showed larger photo-releases of NO3- and PO43-, while NO2- dominated inorganic nutrient releases during groundwater DOM light incubations. Thus, this study concludes that the photoreactivity of DOM closely relates to its original composition and sources.

Higher allochthonous organic carbon increases polycyclic aromatic hydrocarbon concentration whereas fossil fuel combustion alters the composition: Evidence from a eutrophic plateau lake in southwest China.

Understanding the source of polycyclic aromatic hydrocarbons (PAHs) is crucial for determining their structural, degradational, and burial characteristics in lake sediments. Here, we used a sediment core to determine the changing sources and burial characteristics of 16 PAHs from Dianchi Lake, southwest China. The ∑16PAH concentrations ranged from 105.10 to 1248.05 ng g-1 (448.97 ± 351.25 ng g-1), exhibiting a sharp increase since 1976. Our results showed that the depositional flux of PAHs has increased by approximately 3.72 times over the past 114 years (1895-2009). The C/N ratio, stable isotopes (δ13Corg and δ15N), and n-alkanes data all indicated that allochthonous contributors of organic carbon have substantially increased since the 1970s, playing an important role in the increase in sedimentary PAHs. Positive matrix factorization indicated that petrogenic sources, coal and biomass combustion, and traffic emissions were the main sources of PAHs. The relationships between PAHs from different sources and total organic carbon (TOC) varied with the sorption characteristics. The effect of TOC on the absorption of high-molecular-weight aromatic PAHs from fossil fuels was significant. A higher risk of lake eutrophication is accompanied by higher allochthonous organic matter imports, which might stimulate an increase in sedimentary PAHs through algal biomass blooms.

Anthropogenic Activities Generate High-Refractory Black Carbon along the Yangtze River Continuum.

Combustion-driven particulate black carbon (PBC) is a crucial slow-cycling pool in the organic carbon flux from rivers to oceans. Since the refractoriness of PBC stems from the association of non-homologous char and soot, the composition and source of char and soot must be considered when investigating riverine PBC. Samples along the Yangtze River continuum during different hydrological periods were collected in this study to investigate the association and asynchronous combustion drive of char and soot in PBC. The results revealed that PBC in the Yangtze River, with higher refractory nature, accounts for 13.73 ± 6.89% of particulate organic carbon, and soot occupies 37.53 ± 11.00% of PBC. The preponderant contribution of fossil fuel combustion to soot (92.57 ± 3.20%) compared to char (27.55 ± 5.92%), suggested that fossil fuel combustion is a crucial driver for PBC with high soot percentage. Redundancy analysis and structural equation modeling confirmed that the fossil fuel energy used by anthropogenic activities promoting soot is the crucial reason for high-refractory PBC. We estimated that the Yangtze River transported 0.15-0.23 Tg of soot and 0.15-0.25 Tg of char to the ocean annually, and the export of large higher refractory PBC to the ocean can form a long-term sink and prolong the residence time of terrigenous carbon.

Hydrogenotrophic pathway dominates methanogenesis along the river-estuary continuum of the Yangtze River.

Rivers are considered as an important source of methane (CH4) to the atmosphere, but our understanding for the methanogenic pathway in rivers and its linkage with CH4 emission is very limited. Here, we investigated the diffusive flux of CH4 and its stable carbon isotope signature (δ13C-CH4) along the river-estuary continuum of the Yangtze River. The diffusive CH4 flux was estimated to 27.9 ± 11.4 µmol/m2/d and 36.5 ± 24.4 µmol/m2/d in wet season and dry season, respectively. The δ13C-CH4 values were generally lower than -60‰, with the fractionation factor (αc) higher than 1.055 and the isotope separation factor (εc) ranged from 55 to 100. In situ microbial composition showed that hydrogenotrophic methanogens accounts for over 70% of the total reads. Moreover, the incubation test showed that the headspace CH4 concentration by adding CO2/H2 to the sediment was orders of magnitude higher than that by adding trimethylamine and sodium acetate. These results jointly verified the river-estuary continuum is a minor CH4 source and dominated by hydrogenotrophic pathway. Based on the methanogenic pathway here and previous reported data in the same region, the historical variation of diffusive CH4 flux was calculated and results showed that CH4 emission has reduced 82.5% since the construction of Three Gorges Dam (TGD). Our study verified the dominant methanogenic pathway in river ecosystems and clarified the effect and mechanism of dam construction on riverine CH4 emission.

Sandwich Plate Structure Periodically Attached by S-Shaped Oscillators for Low Frequency Ship Vibration Isolation.

Locally resonant phononic crystals are a kind of artificial periodic composite material/structure with an elastic wave band gap that show attractive application potential in low-frequency vibration control. For low-frequency vibration control problems of ship power systems, this paper proposes a phononic crystal board structure, and based on the Bloch theorem of periodic structure, it uses a finite element method to calculate the band structure and the displacement fields corresponding to the characteristic mode and vibration transmission curve of the corresponding finite periodic sandwich plate structure, and the band gap characteristics are studied. The mechanism of band gap formation is mainly attributed to the mode coupling of the phononic crystal plate structure. Numerical results show that the sandwich plate structure has a double periodicity, so it has a multi-stage elastic wave band gap, which can fully inhibit the transmission of flexural waves and isolate the low-frequency flexural vibration. The experimental measurements of flexural vibration transmission spectra were conducted to validate the accuracy and reliability of the numerical calculation method. On this basis, the potential application of the proposed vibration isolation method in a marine power system is discussed. A vibration isolation platform mounted on a steel plate is studied by numerical simulation, which can isolate low-frequency vibration to protect electronic equipment and precision instruments.

Internal loop sustains cyanobacterial blooms in eutrophic lakes: Evidence from organic nitrogen and ammonium regeneration.

Algal bloom species can live upon internal regenerated ammonium (NH4+) for growth during the nitrogen-limited period. However, the linkages between NH4+ regeneration and phytoplankton biomass and community composition dynamics remain largely unknown. To unravel the interactions between NH4+ regeneration and phytoplankton community, we measured water column NH4+ regeneration rates (REGs) during a continuous phytoplankton growing period and a contrast summer/winter turnover in eutrophic Lake Taihu. Measured REGs were higher in summer than in winter and significantly correlated to total phytoplankton biomass, Cyanophyta biomass and its biomass proportions, and the concentrations of particulate nitrogen and dissolved organic carbon as well as the relative abundance of labile components (proteins and lipids). Random forest regression analyses displayed that variation of REGs were mainly controlled by water temperature and algal-related parameters (including chlorophyll a, total phytoplankton biomass, and Cyanophyta biomass). Partial least squares path model further revealed that algal-related parameters were the direct and significant factors regulating REGs, and contributed to the largest effect of the variance in REGs. Of the algal community, Cyanophyta was the dominant phylum to accelerate REGs. Correspondingly, rapid internal NH4+ turnover may strongly support the persistence of cyanobacterial blooms, thus forming a positive feedback between cyanobacterial blooms and REGs during the nitrogen-limited summer months. We therefore deduced that the internal loop between cyanobacterial blooms and REGs during summer may be a key self-maintenance mechanism of continuous cyanobacterial blooms.

Emerging role of dissolved organic nitrogen in supporting algal bloom persistence in Lake Taihu, China: Emphasis on internal transformations.

Dissolved organic nitrogen (DON) accounts for a significant fraction of the dissolved nitrogen (N) pool in eutrophic lakes, and substantial components of DON are available for phytoplankton. However, long-term changes in DON concentrations in eutrophic lakes have been poorly documented, and the particulate-related internal cycling of DON at the molecular level remains unclear. In this study, changes in the concentration of DON during the past 14 years of Lake Taihu, China were analyzed. Algae and sediment suspensions were incubated under summer sunlight to examine transformations of DON (e.g., photodissolution) at the bulk concentration and molecular level. Concentrations of DON in Lake Taihu ranged from 0 to 4.59 mg L-1, with a mean of 0.82 ± 0.60 mg L-1 (n = 3360). Although annual averages of the concentration of DON (n = 240) showed no significant linear variation from 2005 to 2018, the percentage of DON in total dissolved nitrogen (TDN) increased linearly (p < .05) and was maintained at >50% after 2015. Seasonally, DON concentrations were highest in spring (1.10 ± 0.56 mg L-1), followed by winter (0.87 ± 0.58 mg L-1) and summer (0.54 ± 0.37 mg L-1) concentrations, and lowest in autumn (0.44 ± 0.38 mg L-1). Outdoor incubation experiments suggest that both algae and sediment suspensions contribute to significant increases of DON concentrations but contribute to decreases of inorganic N concentrations at the end of incubations. Moreover, the production of DON by algae suspensions differed from that of sediment suspensions, with more labile components released from algae (e.g., proteins and amino acids), while more refractory components were released from sediment suspensions (e.g., lignin with low H/C and O/C). Taken together, these results emphasize the increasing percentage of DON in TDN during 2009-2018 and the different patterns of algae- and sediment-dominated internal DON transformations in Lake Taihu.

In-Depth Characterization of a Pro-Antibody-Drug Conjugate by LC-MS.

Pro-antibody-drug conjugate (PDC) is a hybrid structural format of immunoconjugate, where the structural complexity of pro-antibody and intrinsic heterogeneity of ADCs impose a prominent analytical challenge to the in-depth characterization of PDCs. In the present study, we successfully prepared and characterized PanP-DM1 as a model of PDCs, which is an anti-EGFR pro-antibody following conjugation with DM1 at lysine residues. The drug-to-antibody ratio (DAR) of PanP-DM1 was determined by LC-MS after deglycosylation, and verified by UV/vis spectroscopy. Following reduction or IdeS digestion, the pro-antibody fragments linked with DM1 were investigated by middle-down mass spectrometry. Furthermore, more than 20 modified lysine conjugation sites were determined by peptide mapping after trypsin digestion. Additionally, more than ten glycoforms of PanP-DM1 were also identified and quantified. In summary, critical quality attributes (CQAs) of PDCs including DAR, drug load distribution, and conjugation sites were fully characterized, which would contribute to the development of other PDCs for cancer treatment.

Preparation and characterization of recombinant protein ScFv(CD11c)-TRP2 for tumor therapy from inclusion bodies in Escherichia coli.

Dendritic cells (DCs)-based immunotherapy represents an approach to the prevention and treatment of cancers. Targeting antigens to receptors on DCs can be expected to enhance immune response. We have constructed an expression vector pET32a(+)-ScFv(CD11c)-TRP2 based on a single-chain antibody fragment (ScFv) that targets the high affinity receptor CD11c which is expressed on murine DCs. The 3'-terminal end of the ScFv was ligated to the gene for MHC class I molecule-recognized peptide from mouse tyrosine-related protein 2 (TRP2). Using this vector, we have expressed and purified ScFv(CD11c)-TRP2, a fusion protein that could target TRP2 peptide to CD11c on DCs in vivo to elicit anti-tumor responses. This fusion protein was expressed in inclusion bodies in Escherichia coli BL21(DE3) and was refolded and purified on-column effectively by immobilized metal affinity chromatography using His-tag. Flow cytometry assays showed the specific binding ability of ScFv(CD11c)-TRP2 to DCs, which could be blocked by a hamster anti-mouse CD11c produced by N418 hybridoma. Further studies demonstrated that ScFv(CD11c)-targeted TRP2 peptide processed by DCs was capable of stimulating T cells proliferation. Thus, this fusion protein provides a basis for further research in cancer therapy in vivo.

Preparation and characterization of fusion protein truncated Pseudomonas Exotoxin A (PE38KDEL) in Escherichia coli.

Pseudomonas Exotoxin A (PE) and truncated PE have been used to prepare immunotoxin with monoclonal antibodies. Truncated Pseudomonas Exotoxin A (PE38KDEL) was expressed with the pET-32a(+) vector in Escherichia coli under control of a T7 promoter. The recombinant protein was purified by His-Ni(2+) metal affinity chromatography and gel filtration. The biological activity of PE38KDEL was evaluated by the inhibition assay of protein synthesis in rabbit reticulocyte lysate system, and the cytotoxicity was tested in Hut 102 and hepatocellular cell lines by the MTS assay. PE38KDEL can significantly inhibit luciferase synthesis in cell-free protein synthesis assay and was slightly cytotoxic in the Hut 102 and hepatocellular cell lines. The results suggest that PE38KDEL would be useful for the preparation of more potent immunotoxins.