Discovery and structural mechanism of DNA endonucleases guided by RAGATH-18-derived RNAs.

CRISPR-Cas systems and IS200/IS605 transposon-associated TnpBs have been utilized for the development of genome editing technologies. Using bioinformatics analysis and biochemical experiments, here we present a new family of RNA-guided DNA endonucleases. Our bioinformatics analysis initially identifies the stable co-occurrence of conserved RAGATH-18-derived RNAs (reRNAs) and their upstream IS607 TnpBs with an average length of 390 amino acids. IS607 TnpBs form programmable DNases through interaction with reRNAs. We discover the robust dsDNA interference activity of IS607 TnpB systems in bacteria and human cells. Further characterization of the Firmicutes bacteria IS607 TnpB system (ISFba1 TnpB) reveals that its dsDNA cleavage activity is remarkably sensitive to single mismatches between the guide and target sequences in human cells. Our findings demonstrate that a length of 20 nt in the guide sequence of reRNA achieves the highest DNA cleavage activity for ISFba1 TnpB. A cryo-EM structure of the ISFba1 TnpB effector protein bound by its cognate RAGATH-18 motif-containing reRNA and a dsDNA target reveals the mechanisms underlying reRNA recognition by ISFba1 TnpB, reRNA-guided dsDNA targeting, and the sensitivity of the ISFba1 TnpB system to base mismatches between the guide and target DNA. Collectively, this study identifies the IS607 TnpB family of compact and specific RNA-guided DNases with great potential for application in gene editing.

Epidemiological Survey of Congenital Heart Disease Among Children Aged from 2 to 18 in Suo County, Nagqu, Tibet.

Lin, Tian, Huaping Jia, Yunming Li, Yongxing Xu, Bei Zhao, Dong Zheng, Hongfeng Yan, Meihui Zhao, Yanlei Li, Liping Xia, Fengxia Zhou, Cuiping Liu, Ke Ma, Ma Mi, and Jianwen Gu. Epidemiological survey of congenital heart disease among children aged from 2 to 18 in Suo County, Nagqu, Tibet. High Alt Med Biol. 00:000-000, 2024. Background: Studies have reported the prevalence of congenital heart disease (CHD) in parts of Tibet, but relative epidemiological surveys are rare. We aimed to explore the prevalence of CHD in children and its relationship with family history in Suo County, Nagqu, Tibet, an altitude of 3,980 meters. Methods: We recruited 4,002 children aged 2-18 years. Subjects underwent a family history investigation, cardiac auscultation, and clinical manifestation examination and then received echocardiographic screening. Results: The prevalence of CHD among children in Suo County was 0.97% (39 cases), much higher than the prevalence at sea level. The most common subtype was atrial septal defect, accounting for 53.9% of CHD, followed by patent ductus arteriosus (33.3%) and ventricular septal defect (12.8%). We also found that children whose mothers had previously borne children with CHD had a higher risk of CHD than those without (p = 0.002); other factors related to CHD during pregnancy, such as smoking, drinking, drug use, and viral infection, showed no statistical differences between children with and without CHD. Conclusions: The prevalence of CHD in children in Suo County is much higher than at low altitude, consisting mostly of simple forms with left-to-right shunt, with rare complex CHD. These results support implementing diagnostic and treatment plans to prevent CHD in Suo County.

Relationship between chorioamnionitis or funisitis and lung injury among preterm infants: meta-analysis involved 16 observational studies with 68,397 participants.

BACKGROUND: Chorioamnionitis (CA) can cause multiple organ injuries in premature neonates, particularly to the lungs. Different opinions exist regarding the impact of intrauterine inflammation on neonatal respiratory distress syndrome (NRDS) and bronchopulmonary dysplasia (BPD). We aim to systematically review the relationship between CA or Funisitis (FV) and lung injury among preterm infants. METHODS: We electronically searched PubMed, EMbase, the Cochrane library, CNKI, and CMB for cohort studies from their inception to March 15, 2023. Two reviewers independently screened literature, gathered data, and did NOS scale of included studies. The meta-analysis was performed using RevMan 5.3. RESULTS: Sixteen observational studies including 68,397 patients were collected. Meta-analysis showed CA or FV increased the lung injury risk (OR = 1.43, 95%CI: 1.06-1.92). Except for histological chorioamnionitis (HCA) (OR = 0.72, 95%CI: 0.57-0.90), neither clinical chorioamnionitis (CCA) (OR = 1.86, 95%CI: 0.93-3.72) nor FV (OR = 1.23, 95%CI: 0.48-3.15) nor HCA with FV (OR = 1.85, 95%CI: 0.15-22.63) had statistical significance in NRDS incidence. As a result of stratification by grade of HCA, HCA (II) has a significant association with decreased incidence of NRDS (OR = 0.48, 95%CI: 0.35-0.65). In terms of BPD, there is a positive correlation between BPD and CA/FV (CA: OR = 3.18, 95%CI: 1.68-6.03; FV: OR = 6.36, 95%CI: 2.45-16.52). Among CA, HCA was positively associated with BPD (OR = 2.70, 95%CI: 2.38-3.07), whereas CCA was not associated with BPD (OR = 2.77, 95%CI: 0.68-11.21). HCA and moderate to severe BPD (OR = 25.38, 95%CI: 7.13-90.32) showed a positive correlation, while mild BPD (OR = 2.29, 95%CI: 0.99-5.31) did not. CONCLUSION: Currently, evidence suggests that CA or FV increases the lung injury incidence in premature infants. For different types of CA and FV, HCA can increase the incidence of BPD while decreasing the incidence of NRDS. And this "protective effect" only applies to infants under 32 weeks of age. Regarding lung injury severity, only moderate to severe cases of BPD were positively correlated with CA.

CRISPRimmunity: an interactive web server for CRISPR-associated Important Molecular events and Modulators Used in geNome edIting Tool identifYing.

The CRISPR-Cas system is a highly adaptive and RNA-guided immune system found in bacteria and archaea, which has applications as a genome editing tool and is a valuable system for studying the co-evolutionary dynamics of bacteriophage interactions. Here introduces CRISPRimmunity, a new web server designed for Acr prediction, identification of novel class 2 CRISPR-Cas loci, and dissection of key CRISPR-associated molecular events. CRISPRimmunity is built on a suite of CRISPR-oriented databases providing a comprehensive co-evolutionary perspective of the CRISPR-Cas and anti-CRISPR systems. The platform achieved a high prediction accuracy of 0.997 for Acr prediction when tested on a dataset of 99 experimentally validated Acrs and 676 non-Acrs, outperforming other existing prediction tools. Some of the newly identified class 2 CRISPR-Cas loci using CRISPRimmunity have been experimentally validated for cleavage activity in vitro. CRISPRimmunity offers the catalogues of pre-identified CRISPR systems to browse and query, the collected resources or databases to download, a well-designed graphical interface, a detailed tutorial, multi-faceted information, and exportable results in machine-readable formats, making it easy to use and facilitating future experimental design and further data mining. The platform is available at http://www.microbiome-bigdata.com/CRISPRimmunity. Moreover, the source code for batch analysis are published on Github (https://github.com/HIT-ImmunologyLab/CRISPRimmunity).

PhageTailFinder: A tool for phage tail module detection and annotation.

Decades of overconsumption of antimicrobials in the treatment and prevention of bacterial infections have resulted in the increasing emergence of drug-resistant bacteria, which poses a significant challenge to public health, driving the urgent need to find alternatives to conventional antibiotics. Bacteriophages are viruses infecting specific bacterial hosts, often destroying the infected bacterial hosts. Phages attach to and enter their potential hosts using their tail proteins, with the composition of the tail determining the range of potentially infected bacteria. To aid the exploitation of bacteriophages for therapeutic purposes, we developed the PhageTailFinder algorithm to predict tail-related proteins and identify the putative tail module in previously uncharacterized phages. The PhageTailFinder relies on a two-state hidden Markov model (HMM) to predict the probability of a given protein being tail-related. The process takes into account the natural modularity of phage tail-related proteins, rather than simply considering amino acid properties or secondary structures for each protein in isolation. The PhageTailFinder exhibited robust predictive power for phage tail proteins in novel phages due to this sequence-independent operation. The performance of the prediction model was evaluated in 13 extensively studied phages and a sample of 992 complete phages from the NCBI database. The algorithm achieved a high true-positive prediction rate (>80%) in over half (571) of the studied phages, and the ROC value was 0.877 using general models and 0.968 using corresponding morphologic models. It is notable that the median ROC value of 992 complete phages is more than 0.75 even for novel phages, indicating the high accuracy and specificity of the PhageTailFinder. When applied to a dataset containing 189,680 viral genomes derived from 11,810 bulk metagenomic human stool samples, the ROC value was 0.895. In addition, tail protein clusters could be identified for further studies by density-based spatial clustering of applications with the noise algorithm (DBSCAN). The developed PhageTailFinder tool can be accessed either as a web server (http://www.microbiome-bigdata.com/PHISDetector/index/tools/PhageTailFinder) or as a stand-alone program on a standard desktop computer (https://github.com/HIT-ImmunologyLab/PhageTailFinder).

DBSCAN-SWA: An Integrated Tool for Rapid Prophage Detection and Annotation.

As an intracellular form of a bacteriophage in the bacterial host genome, a prophage usually integrates into bacterial DNA with high specificity and contributes to horizontal gene transfer (HGT). With the exponentially increasing number of microbial sequences uncovered in genomic or metagenomics studies, there is a massive demand for a tool that is capable of fast and accurate identification of prophages. Here, we introduce DBSCAN-SWA, a command line software tool developed to predict prophage regions in bacterial genomes. DBSCAN-SWA runs faster than any previous tools. Importantly, it has great detection power based on analysis using 184 manually curated prophages, with a recall of 85% compared with Phage_Finder (63%), VirSorter (74%), and PHASTER (82%) for (Multi-) FASTA sequences. Moreover, DBSCAN-SWA outperforms the existing standalone prophage prediction tools for high-throughput sequencing data based on the analysis of 19,989 contigs of 400 bacterial genomes collected from Human Microbiome Project (HMP) project. DBSCAN-SWA also provides user-friendly result visualizations including a circular prophage viewer and interactive DataTables. DBSCAN-SWA is implemented in Python3 and is available under an open source GPLv2 license from https://github.com/HIT-ImmunologyLab/DBSCAN-SWA/.

PHISDetector: A Tool to Detect Diverse In Silico Phage-host Interaction Signals for Virome Studies.

Phage-microbe interactions are appealing systems to study coevolution, and have also been increasingly emphasized due to their roles in human health, disease, and the development of novel therapeutics. Phage-microbe interactions leave diverse signals in bacterial and phage genomic sequences, defined as phage-host interaction signals (PHISs), which include clustered regularly interspaced short palindromic repeats (CRISPR) targeting, prophage, and protein-protein interaction signals. In the present study, we developed a novel tool phage-host interaction signal detector (PHISDetector) to predict phage-host interactions by detecting and integrating diverse in silico PHISs, and scoring the probability of phage-host interactions using machine learning models based on PHIS features. We evaluated the performance of PHISDetector on multiple benchmark datasets and application cases. When tested on a dataset of 758 annotated phage-host pairs, PHISDetector yields the prediction accuracies of 0.51 and 0.73 at the species and genus levels, respectively, outperforming other phage-host prediction tools. When applied to on 125,842 metagenomic viral contigs (mVCs) derived from 3042 geographically diverse samples, a detection rate of 54.54% could be achieved. Furthermore, PHISDetector could predict infecting phages for 85.6% of 368 multidrug-resistant (MDR) bacteria and 30% of 454 human gut bacteria obtained from the National Institutes of Health (NIH) Human Microbiome Project (HMP). The PHISDetector can be run either as a web server (http://www.microbiome-bigdata.com/PHISDetector/) for general users to study individual inputs or as a stand-alone version (https://github.com/HIT-ImmunologyLab/PHISDetector) to process massive phage contigs from virome studies.

The Role of Vasoactive Intestinal Peptide and Mast Cells in the Regulatory Effect of Lactobacillus casei ATCC 393 on Intestinal Mucosal Immune Barrier.

Vasoactive intestinal peptide (VIP) plays an important role in the neuro-endocrine-immune system. Mast cells (MCs) are important immune effector cells. This study was conducted to investigate the protective effect of L. casei ATCC 393 on Enterotoxigenic Escherichia coli (ETEC) K88-induced intestinal mucosal immune barrier injury and its association with VIP/MC signaling by in vitro experiments in cultures of porcine mucosal mast cells (PMMCs) and in vivo experiments using VIP receptor antagonist (aVIP) drug. The results showed that compared with the ETEC K88 and lipopolysaccharides (LPS)-induced model groups, VIP pretreatment significantly inhibited the activation of MCs and the release of ß-hexosaminidase (ß-hex), histamine and tryptase. Pretreatment with aVIP abolished the protective effect of L. casei ATCC 393 on ETEC K88-induced intestinal mucosal immune barrier dysfunction in C57BL/6 mice. Also, with the blocking of VIP signal transduction, the ETEC K88 infection increased serum inflammatory cytokines, and the numbers of degranulated MCs in ileum, which were decreased by administration of L. casei ATCC 393. In addition, VIP mediated the regulatory effect of L. casei ATCC 393 on intestinal microbiota in mice. These findings suggested that VIP may mediate the protective effect of L.casei ATCC 393 on intestinal mucosal immune barrier dysfunction via MCs.

Metagenomic analysis reveals oropharyngeal microbiota alterations in patients with COVID-19.

COVID-19 remains a serious emerging global health problem, and little is known about the role of oropharynx commensal microbes in infection susceptibility and severity. Here, we present the oropharyngeal microbiota characteristics identified by shotgun metagenomic sequencing analyses of oropharynx swab specimens from 31 COVID-19 patients, 29 influenza B patients, and 28 healthy controls. Our results revealed a distinct oropharyngeal microbiota composition in the COVID-19 patients, characterized by enrichment of opportunistic pathogens such as Veillonella and Megasphaera and depletion of Pseudopropionibacterium, Rothia, and Streptococcus. Based on the relative abundance of the oropharyngeal microbiome, we built a microbial classifier to distinguish COVID-19 patients from flu patients and healthy controls with an AUC of 0.889, in which Veillonella was identified as the most prominent biomarker for COVID-19 group. Several members of the genus Veillonella, especially Veillonella parvula which was highly enriched in the oropharynx of our COVID-19 patients, were also overrepresented in the BALF of COVID-19 patients, indicating that the oral cavity acts as a natural reservoir for pathogens to induce co-infections in the lungs of COVID-19 patients. We also found the increased ratios of Klebsiella sp., Acinetobacter sp., and Serratia sp. were correlated with both disease severity and elevated systemic inflammation markers (neutrophil-lymphocyte ratio, NLR), suggesting that these oropharynx microbiota alterations may impact COVID-19 severity by influencing the inflammatory response. Moreover, the oropharyngeal microbiome of COVID-19 patients exhibited a significant enrichment in amino acid metabolism and xenobiotic biodegradation and metabolism. In addition, all 26 drug classes of antimicrobial resistance genes were detected in the COVID-19 group, and were significantly enriched in critical cases. In conclusion, we found that oropharyngeal microbiota alterations and functional differences were associated with COVID-19 severity.

Spatiotemporal Distribution Characteristics of Nutrients in the Drowned Tidal Inlet under the Influence of Tides: A Case Study of Zhanjiang Bay, China.

The tidal dynamics and the characteristics of pollutant migration in the drowned-valley tidal inlet, a typical unit of coastal tidal inlets, are strongly influenced by geomorphological features. Along with the development of society and the economy, the hydrodynamic and water quality environment of the tidal inlet is also becoming more disturbed by human activities, such as reclamation of the sea and the construction of large bridges. In this study, a typical drowned-valley tidal inlet, Zhanjiang Bay (ZJB), was selected for the establishment of a model via coupling of a tidal hydrodynamic model and water quality numerical model. This model can be used to simulate the migration and diffusion of pollutants in ZJB. The spatial and temporal variation processes of water quality factors of the bay under the influence of special geomorphic units was simulated at the tidal-inlet entrance, the flood/ebb tidal delta, and the tidal basin. The results show that ZJB has strong tidal currents that are significantly affected by the terrain. Under the influence of the terrain and tidal currents, the phosphorus and nitrogen concentration at the flood-tide and ebb-tide moments showed obvious temporal and spatial differences in the ebb-tide delta, tidal-inlet entrance, flood-tide delta, and tidal basin. In this study, we analyzed the response mechanism of the water quality environment to the drowned-valley tidal inlet, and this can provide theoretical guidance and a basis for decision-making toward protecting the ecology and water security of ZJB.

Phosphate distribution and sources in the waters of Huangbai River, China: using oxygen isotope composition of phosphate as a tracer.

We investigated the distributions of phosphate (PO4-P) and used the oxygen isotope composition of phosphate (δ18OP) to quantify PO4-P sources in the waters of Huangbai River. According to the environmental characteristics of Huangbai River basin, the sampling stations in the Huangbai River were divided into three groups: sampling stations in the phosphate mining area, in the outcrop area of phosphate rock, and in the residential/agricultural area. The average PO4-P concentration was highest (2.34 ± 1.00 µmol/L) in the outcrop area of phosphate ore, intermediate in the residential/agricultural area (1.06 ± 1.21 µmol/L), and lowest in the phosphate mining area (0.58 ± 0.31 µmol/L). The δ18OP measured in the Huangbai River waters ranged from 6.0 to 20.9‰, with the highest average value in the outcrop area of phosphate rock (average: 14.6‰ ± 3.1‰). The majority of the measured δ18OP values in the Huangbai River deviated greatly from the expected equilibrium values, indicating that δ18OP in this area could be used to trace PO4-P sources. We used two end-member mixing models to quantify the contribution of PO4-P from different sources. In the phosphate mining area, the average fractions of PO4-P from phosphate ore and sewage were 49.5% ± 23.8% and 50.5% ± 23.8%, respectively. In the outcrop area of phosphate rock, the average fractions of PO4-P from phosphate ore and sewage were 60.1% ± 21.7% and 39.9% ± 21.7%, respectively. In the residential/agricultural area, the average fractions of PO4-P from fertilizer and sewage were 49.2% ± 23.2% and 50.8% ± 23.2%, respectively. These results indicate that phosphate mining activities was not an important source for PO4-P in the waters of Huangbai River. The natural weathering of phosphate rock, fertilization, and domestic sewage contributed more to the high PO4-P concentrations in the Huangbai River waters.

Distribution, source and pollution assessment of heavy metals in the surface sediments of the Yangtze River Estuary and its adjacent East China Sea.

The geochemical characteristics of heavy metals (Cd, Co, Cr, Cu, Ti, Zn) in 61 surface sediments from the Yangtze River Estuary and its adjacent East China Sea were studied. The high values of Cu, Co and Zn are distributed near the mouth of Hangzhou Bay. The high values of Cr appear near Zhoushan Archipelago. The high values of Cd appear in the Yangtze River Estuary, while Ti and Cd have high values in the open sea eastward. The order of pollution degree is Cr > Cd > Co > Zn > Ti > Cu. The enrichment degree is Cd > Cr > Zn > Co > Ti > Cu. Except for some sites, Cd is moderately enriched, but there is no severe enrichment. The main sources of human activities of the six metals include industry and shipping. Agricultural production may be another important source of human activities for Cd.

Adaptive immune responses to SARS-CoV-2 infection in severe versus mild individuals.

The global Coronavirus disease 2019 (COVID-19) pandemic caused by SARS-CoV-2 has affected more than eight million people. There is an urgent need to investigate how the adaptive immunity is established in COVID-19 patients. In this study, we profiled adaptive immune cells of PBMCs from recovered COVID-19 patients with varying disease severity using single-cell RNA and TCR/BCR V(D)J sequencing. The sequencing data revealed SARS-CoV-2-specific shuffling of adaptive immune repertories and COVID-19-induced remodeling of peripheral lymphocytes. Characterization of variations in the peripheral T and B cells from the COVID-19 patients revealed a positive correlation of humoral immune response and T-cell immune memory with disease severity. Sequencing and functional data revealed SARS-CoV-2-specific T-cell immune memory in the convalescent COVID-19 patients. Furthermore, we also identified novel antigens that are responsive in the convalescent patients. Altogether, our study reveals adaptive immune repertories underlying pathogenesis and recovery in severe versus mild COVID-19 patients, providing valuable information for potential vaccine and therapeutic development against SARS-CoV-2 infection.

Spatial and Seasonal Variations of Sedimentary Organic Matter in a Subtropical Bay: Implication for Human Interventions.

Elemental (total organic carbon (TOC) and total nitrogen (TN)) and stable carbon and nitrogen isotope compositions (δ13C and δ15N, respectively) in the surface sediment of Zhanjiang Bay (ZJB) in spring and summer were measured to study the spatial and seasonal changes of organic matter (OM) and assess the human-induced and environment-induced changes in the area. The OM in the surface sediment of ZJB was a mixture of terrestrial and marine sources, and was dominated by marine OM (54.9% ± 15.2%). Compared to the central ZJB, the channel and coastal ZJB areas had higher δ13C and δ15N values, higher TOC and TN concentrations, and lower TOC/TN ratios, indicating higher primary productivity and higher percentages of marine OM in the latter two subregions. Mariculture activities, sewage inputs, and dredging were responsible for these phenomena. Clear seasonal variations in OM were observed in ZJB. The average proportions of terrestrial OM in summer increased by 10.2% in the ZJB channel and 26.0% in the coastal ZJB area compared with those in spring. Heavy rainfall brought a large amount of terrestrial OM into the channel and coastal ZJB areas, leading to the increase of the terrestrial OM fraction in these two subregions in summer. In summary, anthropogenic influences had a significant influence on the spatial and seasonal variations of sedimentary OM in ZJB.

An anti-CRISPR protein disables type V Cas12a by acetylation.

Phages use anti-CRISPR proteins to deactivate the CRISPR-Cas system. The mechanisms for the inhibition of type I and type II systems by anti-CRISPRs have been elucidated. However, it has remained unknown how the type V CRISPR-Cas12a (Cpf1) system is inhibited by anti-CRISPRs. Here we identify the anti-CRISPR protein AcrVA5 and report the mechanisms by which it inhibits CRISPR-Cas12a. Our structural and biochemical data show that AcrVA5 functions as an acetyltransferase to modify Moraxella bovoculi (Mb) Cas12a at Lys635, a residue that is required for recognition of the protospacer-adjacent motif. The AcrVA5-mediated modification of MbCas12a results in complete loss of double-stranded DNA (dsDNA)-cleavage activity. In contrast, the Lys635Arg mutation renders MbCas12a completely insensitive to inhibition by AcrVA5. A cryo-EM structure of the AcrVA5-acetylated MbCas12a reveals that Lys635 acetylation provides sufficient steric hindrance to prevent dsDNA substrates from binding to the Cas protein. Our study reveals an unprecedented mechanism of CRISPR-Cas inhibition and suggests an evolutionary arms race between phages and bacteria.

CRISPRminer is a knowledge base for exploring CRISPR-Cas systems in microbe and phage interactions.

CRISPR-Cas systems not only play key roles in prokaryotic acquired immunity, but can also be adapted as powerful genome editing tools. Understanding the native role of CRISPR-Cas systems in providing adaptive immunity can lead to new CRISPR-based technologies. Here, we develop CRISPRminer, a knowledge base and web server to comprehensively collect and investigate the knowledge of CRISPR-Cas systems and generate instructive annotations, including CRISPR arrays and Cas protein annotation, CRISPR-Cas system classification, self-targeting events detection, microbe-phage interaction inference, and anti-CRISPR annotation. CRISPRminer is user-friendly and freely available at http://www.microbiome-bigdata.com/CRISPRminer.

Spatial distribution and correlation characteristics of heavy metals in the seawater, suspended particulate matter and sediments in Zhanjiang Bay, China.

Concentrations of eight heavy metals (i.e., Fe, Mn, Cr, Ni, Cu, Zn, Cd and Pb) in the seawater, suspended particulate matter (SPM) and sediments of the Zhanjiang Bay were investigated in 2014. The concentrations of metals were generally low in the seawater and sediments of the Zhanjiang Bay in winter and summer, indicating good environmental quality in the bay. The distribution patterns of Fe and Mn in three phases indicated the influence of terrestrial inputs. The partition coefficients log(Kd) between the dissolved and particulate phases showed a general decrease in the order of Pb≈Cd>Fe≈Mn>Ni≈Cr>Zn>Cu. The concentrations of some metals in the dissolved and particulate phases showed seasonal variations. Phytoplankton production and complexation reactions may contribute to this phenomenon. The relationships among metals in different phases were different, and there were few close relationships among metals in the dissolved phase, many close relationships in the particulate phase, and more close relationships in the sedimentary phase. This finding may be related to the different mobility levels of metals in different phases.

The distribution and seasonal variations of sedimentary organic matter in the East China Sea shelf.

We sampled the surface sediments of the East China Sea shelf (ECSS) in spring and autumn, 2014, and analyzed the biogenic element concentrations and stable carbon (δ13C) and nitrogen (δ15N) isotopic compositions to study the distribution and seasonal variations of sedimentary organic matter (OM). The average concentrations of TOC, TN and OP in autumn decreased obviously compared with those in spring. The increase of δ15N values in autumn indicated the priority utilization of 14N by bacterial decomposition activity. The values of δ13C were used to trace organic matter sources. The estimated percentages for terrestrial OM were in the range of 0-34.6%. They generally decreased seaward in nearshore areas, indicating the decrease of terrigenous influence. There was an obvious tongue-shaped region with relatively low percentages of terrestrial OM (<12%) in the northern part of the ECSS, which may be a reflection of the intrusion pathway of the outer seawater.

Potential mobility of inorganic nutrients and its controls at the sediment-water interface in the main path of Kuroshio Current off eastern Taiwan.

Surface sediments were collected from the main path of Kuroshio Current (KC) off eastern Taiwan (ETW), and laboratory incubation was conducted for the study of the nutrient exchange at the sediment-water interface. Exchange fluxes of NO3--N, NO2--N, NH4+-N, PO43--P and SiO32--Si under simulated site condition were -0.0866, 0.00146, 0.0634, -0.00812 and -0.181mmolm-2d-1, respectively. This indicated that sediments in the studied area might act as a source of NO2--N and NH4+-N and a sink of NO3--N, PO43--P and SiO32--Si. Factors affecting nutrient exchange fluxes were studied by changing incubation conditions. Compared with some coastal areas in China, the main path of KC off ETW showed relatively low nutrient exchange fluxes at the sediment-water interface. It could be inferred that the sediment-water exchange of nutrients in the main path of KC off ETW had little influence on the downstream nutrient transportation by KC year-round based on the results of this research.