Targeting KDM4A epigenetically activates tumor-cell-intrinsic immunity by inducing DNA replication stress.

Developing strategies to activate tumor-cell-intrinsic immune response is critical for improving tumor immunotherapy by exploiting tumor vulnerability. KDM4A, as a histone H3 lysine 9 trimethylation (H3K9me3) demethylase, has been found to play a critical role in squamous cell carcinoma (SCC) growth and metastasis. Here we report that KDM4A inhibition promoted heterochromatin compaction and induced DNA replication stress, which elicited antitumor immunity in SCC. Mechanistically, KDM4A inhibition promoted the formation of liquid-like HP1γ puncta on heterochromatin and stall DNA replication, which activated tumor-cell-intrinsic cGAS-STING signaling through replication-stress-induced cytosolic DNA accumulation. Moreover, KDM4A inhibition collaborated with PD1 blockade to inhibit SCC growth and metastasis by recruiting and activating CD8+ T cells. In vivo lineage tracing demonstrated that KDM4A inhibition plus PD1 blockade efficiently eliminated cancer stem cells. Altogether, our results demonstrate that targeting KDM4A can activate anti-tumor immunity and enable PD1 blockade immunotherapy by aggravating replication stress in SCC cells.

Diatom bloom trigger notable variations in microzooplanktonic ciliate composition, body-size spectrum and biotic-abiotic interaction in the Arctic Ocean.

How microzooplanktonic ciliate adaptative strategies differ across diatom bloom and non-diatom bloom areas in the Arctic Ocean remains poorly documented. To address this gap, two different situations were categorized in the Arctic Ocean at summer 2023: diatom bloom stations (DBS) (genus Thalassiosira, chain-like) and non-diatom bloom stations (nDBS). Total abundance of ciliate at 3 m and 25 m in DBS was 2.8 and 1.8 folds higher than in nDBS, respectively. Aloricate ciliates were singled out in both DBS and nDBS, whilst their average abundance and biomass of large size-fraction (>50 µm) in former were 4.5-5.6 folds higher than in latter. Regarding tintinnids, high abundance of Ptychocylis acuta (Bering Strait species) mainly occurred at DBS, coupled with distribution of co-occurring Pacific-origin species Salpingella sp.1, collectively suggested a strong intrusion of Pacific Inflow during summer 2023. Additionally, presence of high abundance of Acanthostomella norvegica and genus Parafavella in nDBS might indicate the trajectory of the Transpolar Drift. Alternatively, tintinnids can serve as credible bioindicators for either monitoring currents or evaluating microzooplankton Borealization. Average abundance of total ciliate within 15-135 µm body-size spectrum in DBS was higher than nDBS. Moreover, spearman's rank correlation between biotic and abiotic analysis revealed that temperature and dissolved oxygen at DBS determined tintinnid species richness and ciliate total abundance, respectively. The results clearly demonstrate that remarkable divergences in large size-fraction of ciliate abundance between DBS and nDBS validate their irreplaceable role in controlling phytoplankton outbreak and associated biological processes in polar seas.

FADD amplification is associated with CD8+ T-cell exclusion and malignant progression in HNSCC.

OBJECTIVE: This study aimed to clarify the relationship between FADD amplification and overexpression and the tumor immune microenvironment. METHODS: Immunohistochemical staining and bioanalysis were used to analyze the association between FADD expression in tumor cells and cells in tumor microenvironment. RNA-seq analysis was used to detect the differences in gene expression upon FADD overexpression. Flow cytometry and multicolor immunofluorescence staining (mIHC) were used to detect the differences in CD8+ T-cell infiltration in FADD-overexpressed cells or tumor tissues. RESULTS: Overexpression of FADD significantly promoted tumor growth. Cells with high FADD expression presented high expression of CD276 and FGFBP1 and low expression of proinflammatory factors (such as IFIT1-3 and CXCL8), which reduced the percentage of CD8+ T cells and created a "cold tumor" immune microenvironment, thus promoting tumor progression. In vivo and in vitro experiment confirmed that tumor tissues with excessive FADD expression exhibited CD8+ T-cell exclusion in the microenvironment. CONCLUSION: Our preliminary investigation has discovered the association between FADD expression and the immunosuppressive microenvironment in HNSCC. Due to the high frequent amplification of the chromosomal region 11q13.3, where FADD is located, targeting FADD holds promise for improving the immune-inactive state of tumors, subsequently inhibiting HNSCC tumor progression.

Enhanced resolution of marine viruses with violet side scatter.

Marine viruses make up an essential compartment of the marine ecosystem. They are the most abundant organisms and represent one of the biggest sources of unknown biodiversity. Viruses also have an important impact on bacterial and algal mortality in the ocean, and as such have a major influence on microbial diversity and biogeochemical cycling. However, little is known about the abundance and distribution patterns of viruses across the oceans and seas. Over the last 20 years, flow cytometry has been the technique of choice to detect and count the viral particles in natural samples. Nevertheless, due to their small size, the detection of marine viruses is still extremely challenging. In this article we describe how a new generation of flow cytometer which uses the side scatter (SSC) of violet photons from a 405 nm laser beam helps to improve the resolution for detecting marine viruses. To the best of our knowledge, this is the first report where virioplankton has been detected in aquatic samples using flow cytometry with a 405 nm violet SSC instead of a 488 nm blue SSC.

Palbociclib-based high-throughput combination drug screening identifies synergistic therapeutic options in HPV-negative head and neck squamous cell carcinoma.

BACKGROUND: Deregulation of cell-cycle pathway is ubiquitously observed in human papillomavirus negative (HPVneg) head and neck squamous cell carcinoma (HNSCC). Despite being an attractive target, CDK4/6 inhibition using palbociclib showed modest or conflicting results as monotherapy or in combination with platinum-based chemotherapy or cetuximab in HPVneg HNSCC. Thus, innovative agents to augment the efficacy of palbociclib in HPVneg HNSCC would be welcomed. METHODS: A collection of 162 FDA-approved and investigational agents was screened in combinatorial matrix format, and top combinations were validated in a broader panel of HPVneg HNSCC cell lines. Transcriptional profiling was conducted to explore the molecular mechanisms of drug synergy. Finally, the most potent palbociclib-based drug combination was evaluated and compared with palbociclib plus cetuximab or cisplatin in a panel of genetically diverse HPVneg HNSCC cell lines and patient-derived xenograft models. RESULTS: Palbociclib displayed limited efficacy in HPVneg HNSCC as monotherapy. The high-throughput combination drug screening provided a comprehensive palbociclib-based drug-drug interaction dataset, whereas significant synergistic effects were observed when palbociclib was combined with multiple agents, including inhibitors of the PI3K, EGFR, and MEK pathways. PI3K pathway inhibitors significantly reduced cell proliferation and induced cell-cycle arrest in HPVneg HNSCC cell lines when combined with palbociclib, and alpelisib (a PI3Kα inhibitor) was demonstrated to show the most potent synergy with particularly higher efficacy in HNSCCs bearing PIK3CA alterations. Notably, when compared with cisplatin and cetuximab, alpelisib exerted stronger synergism in a broader panel of cell lines. Mechanistically, RRM2-dependent epithelial mesenchymal transition (EMT) induced by palbociclib, was attenuated by alpelisib and cetuximab rather than cisplatin. Subsequently, PDX models with distinct genetic background further validated that palbociclib plus alpelisib had significant synergistic effects in models harboring PIK3CA amplification. CONCLUSIONS: This study provides insights into the systematic combinatory effect associated with CDK4/6 inhibition and supports further initiation of clinical trials using the palbociclib plus alpelisib combination in HPVneg HNSCC with PIK3CA alterations.

Mineralocorticoid receptor negatively regulates angiogenesis through repression of STAT3 activity in endothelial cells.

The mineralocorticoid receptor (MR) plays important roles in cardiovascular pathogenesis. The function of MR in angiogenesis is still controversial. This study aimed to explore the role of endothelial MR in angiogenesis and to delineate the underlying mechanism. Endothelial-hematopoietic MR knockout (EMRKO) mice were generated and subjected to hindlimb ischemia and injection of melanoma cells. Laser Doppler measurements showed that EMRKO mice had improved blood flow recovery and increased vessel density in ischemic limbs. In addition, EMRKO accelerated growth and increased the vessel density of tumors. Matrigel implantation, aortic ring assays, and tube formation assays demonstrated that MRKO endothelial cells (ECs) manifested increased angiogenic potential. MRKO ECs also displayed increased migration ability and proliferation. MRKO and MR knockdown both upregulated gene expression, protein level, and phosphorylation of signal transducer and activator of transcription 3 (STAT3). Stattic, a selective STAT3 inhibitor, attenuated the effects of MRKO on tube formation, migration, and proliferation of ECs. At the molecular level, MR interacted with CCAAT enhancer-binding protein beta (C/EBPß) to suppress the transcription of STAT3. Furthermore, interactions between MR and STAT3 blocked the phosphorylation of STAT3. Finally, stattic abolished the pro-angiogenic phenotype of EMRKO mice. Taken together, endothelial MR is a negative regulator of angiogenesis, likely in a ligand-independent manner. Mechanistically, MR downregulates STAT3 that mediates the impacts of MR deficiency on the angiogenic activity of ECs and angiogenesis. Targeting endothelial MR may be a potential pro-angiogenic strategy for ischemic diseases. © 2019 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Elevated sodium chloride drives type I interferon signaling in macrophages and increases antiviral resistance.

Type I IFN production and signaling in macrophages play critical roles in innate immune responses. High salt (i.e. high concentrations of NaCl) has been proposed to be an important environmental factor that influences immune responses in multiple ways. However, it remains unknown whether high salt regulates type I IFN production and signaling in macrophages. Here, we demonstrated that high salt promoted IFNß production and its signaling in both human and mouse macrophages, and consequentially primed macrophages for strengthened immune sensing and signaling when challenged with viruses or viral nucleic acid analogues. Using both pharmacological inhibitors and RNA interference we showed that these effects of high salt on IFNß signaling were mediated by the p38 MAPK/ATF2/AP1 signaling pathway. Consistently, high salt increased resistance to vesicle stomatitis virus (VSV) infection in vitro. In vivo data indicated that a high-salt diet protected mice from lethal VSV infection. Taken together, these results identify high salt as a crucial regulator of type I IFN production and signaling, shedding important new light on the regulation of innate immune responses.

T-Cell Mineralocorticoid Receptor Controls Blood Pressure by Regulating Interferon-Gamma.

RATIONALE: Hypertension remains to be a global public health burden and demands novel intervention strategies such as targeting T cells and T-cell-derived cytokines. Mineralocorticoid receptor (MR) antagonists have been clinically used to treat hypertension. However, the function of T-cell MR in blood pressure (BP) regulation has not been elucidated. OBJECTIVE: We aim to determine the role of T-cell MR in BP regulation and to explore the mechanism. METHODS AND RESULTS: Using T-cell MR knockout mouse in combination with angiotensin II-induced hypertensive mouse model, we demonstrated that MR deficiency in T cells strikingly decreased both systolic and diastolic BP and attenuated renal and vascular damage. Flow cytometric analysis showed that T-cell MR knockout mitigated angiotensin II-induced accumulation of interferon-gamma (IFN-γ)-producing T cells, particularly CD8+ population, in both kidneys and aortas. Similarly, eplerenone attenuated angiotensin II-induced elevation of BP and accumulation of IFN-γ-producing T cells in wild-type mice. In cultured CD8+ T cells, T-cell MR knockout suppressed IFN-γ expression whereas T-cell MR overexpression and aldosterone both enhanced IFN-γ expression. At the molecular level, MR interacted with NFAT1 (nuclear factor of activated T-cells 1) and activator protein-1 in T cells. Finally, T-cell MR overexpressing mice manifested more elevated BP compared with control mice after angiotensin II infusion and such difference was abolished by IFN-γ-neutralizing antibodies. CONCLUSIONS: MR may interact with NFAT1 and activator protein-1 to control IFN-γ in T cells and to regulate target organ damage and ultimately BP. Targeting MR in T cells specifically may be an effective novel approach for hypertension treatment.

Mineralocorticoid Receptor Deficiency in Macrophages Inhibits Atherosclerosis by Affecting Foam Cell Formation and Efferocytosis.

Mineralocorticoid receptor (MR) has been considered as a potential target for treating atherosclerosis. However, the cellular and molecular mechanisms are not completely understood. We aim to explore the functions and mechanisms of macrophage MR in atherosclerosis. Atherosclerosis-susceptible LDLRKO chimeric mice with bone marrow cells from floxed control mice or from myeloid MR knock-out (MRKO) mice were generated and fed with high cholesterol diet. Oil red O staining showed that MRKO decreased atherosclerotic lesion area in LDLRKO mice. In another mouse model of atherosclerosis, MRKO/APOEKO mice and floxed control/APOEKO mice were generated and treated with angiotensin II. Similarly, MRKO inhibited the atherosclerotic lesion area in APOEKO mice. Histological analysis showed that MRKO increased collagen coverage and decreased necrosis and macrophage accumulation in the lesions. In vitro results demonstrated that MRKO suppressed macrophage foam cell formation and up-regulated the expression of genes involved in cholesterol efflux. Furthermore, MRKO decreased accumulation of apoptotic cells and increased effective efferocytosis in atherosclerotic lesions. In vitro study further revealed that MRKO increased the phagocytic index of macrophages without affecting their apoptosis. In conclusion, MRKO reduces high cholesterol- or angiotensin II-induced atherosclerosis and favorably changes plaque composition, likely improving plaque stability. Mechanistically, MR deficiency suppresses macrophage foam cell formation and up-regulates expression of genes related to cholesterol efflux, as well as increases effective efferocytosis and phagocytic capacity of macrophages.

Three rDNA Loci-Based Phylogenies of Tintinnid Ciliates (Ciliophora, Spirotrichea, Choreotrichida).

To improve understanding of diversity, phylogeny and evolution in tintinnid ciliates, it is essential to link multiple molecular markers with properly identified and documented morphospecies. Accordingly, 54 tintinnid morphospecies/isolates mainly from the Yellow and East China Seas were collected and analysed. Using single-cell approaches, sequences were obtained for three rDNA loci (18S, ITS1-5.8S-ITS2, D1-D5 region of 28S). Twenty-six tintinnid morphospecies (29 isolates) are documented by micrographs, measurements, morphologically described, and compared with the original species description. Three rDNA loci-based phylogenetic analyses were then performed for these identified isolates. Sequences from 25 unidentified species/isolates were also included in the comparison of the three rDNA loci. Ribosomal DNA genes of the genus Leprotintinnus were analysed for the first time, showing that Leprotintinnus was closely related to Tintinnopsis radix and branched distinctly apart from the family Tintinnidiidae. Four novel clades (VI to IX) of the Tintinnopsis complex emerged in the 18S genealogies. Analyses of the relative variability in the ITS and 28S regions vs. the 18S rDNA showed that the ITS1-5.8S-ITS2 and ITS2 regions well co-varied with the 18S rDNA when the variations of the latter were less than 3%, whereas at difference of less than 1%, no correlation was found between the compared loci. These findings highlight the difficulties in using variable locus-based cut-off divergences in circumscribing tintinnid morphospecies.

Mineralocorticoid Receptor Deficiency in Macrophages Inhibits Neointimal Hyperplasia and Suppresses Macrophage Inflammation Through SGK1-AP1/NF-κB Pathways.

OBJECTIVE: Restenosis after percutaneous coronary intervention remains to be a serious medical problem. Although mineralocorticoid receptor (MR) has been implicated as a potential target for treating restenosis, the cellular and molecular mechanisms are largely unknown. This study aims to explore the functions of macrophage MR in neointimal hyperplasia and to delineate the molecular mechanisms. APPROACH AND RESULTS: Myeloid MR knockout (MMRKO) mice and controls were subjected to femoral artery injury. MMRKO reduced intima area and intima/media ratio, Ki67- and BrdU-positive vascular smooth muscle cells, expression of proinflammatory molecules, and macrophage accumulation in injured arteries. MMRKO macrophages migrated less in culture. MMRKO decreased Ki67- and BrdU-positive macrophages in injured arteries. MMRKO macrophages were less Ki67-positive in culture. Conditioned media from MMRKO macrophages induced less migration, Ki67 positivity, and proinflammatory gene expression of vascular smooth muscle cells. After lipopolysaccharide treatment, MMRKO macrophages had decreased p-cFos and p-cJun compared with control macrophages, suggesting suppressed activation of activator protein-1 (AP1). Nuclear factor-κB (NF-κB) pathway was also inhibited by MMRKO, manifested by decreased p-IκB kinase-ß and p-IκBα, increased IκBα expression, decreased nuclear translocation of p65 and p50, as welll as decreased phosphorylation and expression of p65. Finally, overexpression of serum-and-glucocorticoid-inducible-kinase-1 (SGK1) attenuated the effects of MR deficiency in macrophages. CONCLUSIONS: Selective deletion of MR in myeloid cells limits macrophage accumulation and vascular inflammation and, therefore, inhibits neointimal hyperplasia and vascular remodeling. Mechanistically, MR deficiency suppresses migration and proliferation of macrophages and leads to less vascular smooth muscle cell activation. At the molecular level, MR deficiency suppresses macrophage inflammatory response via SGK1-AP1/NF-κB pathways.

Composition, diel dynamic and biotic-abiotic interaction of marine neustonic zooplankton in the oligotrophic South China Sea.

Neuston, situated at the air-sea interface, stands as a crucial frontier in the realm of the global warming. Despite its unique habitat, there remains a need to substantiate the composition, diel dynamic and biotic-abiotic interaction of neustonic zooplankton in the tropical seas. In this study, we present rare observational data on neustonic zooplankton (0-20 cm) in the oligotrophic tropical South China Sea (SCS) during the summer of 2022. A total of eighteen samples were collected and analyzed, revealing the presence of fourteen taxa from eight phyla. The most prevalent group was Cypridina, accounting for 33.7% of the total abundance, followed by copepods (29.0%) and jellyfish (10.9%). Within copepods, the genus Pontella exhibited the highest relative abundance (38.0%). Additionally, each neuston taxon displayed unique diel distribution patterns. Cypridina was the most abundant taxon during the night (40.4%), while it shifted to copepod dominance during the day (50.4%). Among copepods, genus Pontella and larvae were dominant groups at night (44.7%) and during the day (30.0%), respectively. Moreover, a multivariate biota-environment analysis demonstrated that temperature, pH, dissolved oxygen and Si(OH)4 significantly impacted neuston composition. Notably, both jellyfish and sea snails showed a significant positive correlation with temperature, suggesting their potential dominance in the neuston community in response to future global warming in the oligotrophic tropical seas. This study lays a robust foundation for recognizing the neuston community in the oceanic SCS, and helps evaluate the long-term risks to neuston habitats under climate changes.

Stabilization of EREG via STT3B-mediated N-glycosylation is critical for PDL1 upregulation and immune evasion in head and neck squamous cell carcinoma.

Dysregulated Epiregulin (EREG) can activate epidermal growth factor receptor (EGFR) and promote tumor progression in head and neck squamous cell carcinoma (HNSCC). However, the mechanisms underlying EREG dysregulation remain largely unknown. Here, we showed that dysregulated EREG was highly associated with enhanced PDL1 in HNSCC tissues. Treatment of HNSCC cells with EREG resulted in upregulated PDL1 via the c-myc pathway. Of note, we found that N-glycosylation of EREG was essential for its stability, membrane location, biological function, and upregulation of its downstream target PDL1 in HNSCC. EREG was glycosylated at N47 via STT3B glycosyltransferases, whereas mutations at N47 site abrogated N-glycosylation and destabilized EREG. Consistently, knockdown of STT3B suppressed glycosylated EREG and inhibited PDL1 in HNSCC cells. Moreover, treatment of HNSCC cells with NGI-1, an inhibitor of STT3B, blocked STT3B-mediated glycosylation of EREG, leading to its degradation and suppression of PDL1. Finally, combination of NGI-1 treatment with anti-PDLl therapy synergistically enhanced the efficacy of immunotherapy of HNSCC in vivo. Taken together, STT3B-mediated N-glycosylation is essential for stabilization of EREG, which mediates PDL1 upregulation and immune evasion in HNSCC.

Latitudinal pronounced variations in tintinnid (Ciliophora) community at surface waters from the South China Sea to the Yellow Sea: Oceanic-to-neritic species shift, biotic-abiotic interaction and future prediction.

The oceanic-to-neritic species shift of microzooplanktonic tintinnids and their interaction with relevant abiotic variables are two crucial processes in the marine ecosystem. However, these processes remain poorly documented in China's marginal seas. In the summer of 2022, we investigated the community structure of pelagic tintinnids in surface waters from the South China Sea (SCS) to the Yellow Sea (YS), passing through the East China Sea (ECS). A number of 58 species from 23 genera were identified, with 36 and 22 species belonging to oceanic and neritic genera, respectively. The abundance proportion of oceanic and neritic genera exhibited a decreasing and increasing trend, respectively, from the SCS to YS. Furthermore, four distinctive tintinnid community groups were classified based on cluster analysis using tintinnid species and abundance data, and the position of southern Taiwan Strait was identified as the "Shift Point" for oceanic-to-neritic species dominance. The top two tintinnid species in each group showed distinct variations in body size. Additionally, multivariate biotic-abiotic statistical analyses revealed that temperature determined tintinnid species richness, while temperature, salinity, Si(OH)4, and Chl a determined tintinnid abundance. Our study provides a substantial foundation for recognizing the oceanic-to-neritic species shift of tintinnids in the China's marginal seas, and highlights the role of biotic-abiotic factors in driving biogeochemical fluxes and the potential response of microzooplankton to future climate change.

Alterations of oral and gut viromes in hypertension and/or periodontitis.

The microbiota plays an important role in both hypertension (HTN) and periodontitis (PD), and PD exacerbates the development of HTN by oral and gut microbiota. Previous studies have focused on exploring the importance of the bacteriome in HTN and PD but overlooked the impact of the virome, which is also a member of the microbiota. We collected 180 samples of subgingival plaques, saliva, and feces from a cohort of healthy subjects (nHTNnPD), subjects with HTN (HTNnPD) or PD (PDnHTN), and subjects with both HTN and PD (HTNPD). We performed metagenomic sequencing to assess the roles of the oral and gut viromes in HTN and PD. The HTNnPD, PDnHTN, and HTNPD groups all showed significantly distinct beta diversity from the nHTNnPD group in saliva. We analyzed alterations in oral and gut viral composition in HTN and/or PD and identified significantly changed viruses in each group. Many viruses across three sites were significantly associated with blood pressure and other clinical parameters. Combined with these clinical associations, we found that Gillianvirus in subgingival plaques was negatively associated with HTN and that Torbevirus in saliva was positively associated with HTN. We found that Pepyhexavirus from subgingival plaques was indicated to be transferred to the gut. We finally evaluated viral-bacterial transkingdom interactions and found that viruses and bacteria may cooperate to affect HTN and PD. Correspondingly, HTN and PD may synergize to improve communications between viruses and bacteria.IMPORTANCEPeriodontitis (PD) and hypertension (HTN) are both highly prevalent worldwide and cause serious adverse outcomes. Increasing studies have shown that PD exacerbates HTN by oral and gut microbiota. Previous studies have focused on exploring the importance of the bacteriome in HTN and PD but overlooked the impact of the virome, even though viruses are common inhabitants in humans. Alterations in oral and gut viral diversity and composition contribute to diseases. The present study, for the first time, profiled the oral and gut viromes in HTN and/or PD. We identified key indicator viruses and their clinical implications in HTN and/or PD. We also investigated interactions between viruses and bacteria. This work improved the overall understanding of the viromes in HTN and PD, providing vital insights into the role of the virome in the development of HTN and PD.

Periodontitis exacerbates pulmonary hypertension by promoting IFNγ+ T cell infiltration in mice.

Uncovering the risk factors of pulmonary hypertension and its mechanisms is crucial for the prevention and treatment of the disease. In the current study, we showed that experimental periodontitis, which was established by ligation of molars followed by orally smearing subgingival plaques from patients with periodontitis, exacerbated hypoxia-induced pulmonary hypertension in mice. Mechanistically, periodontitis dysregulated the pulmonary microbiota by promoting ectopic colonization and enrichment of oral bacteria in the lungs, contributing to pulmonary infiltration of interferon gamma positive (IFNγ+) T cells and aggravating the progression of pulmonary hypertension. In addition, we identified Prevotella zoogleoformans as the critical periodontitis-associated bacterium driving the exacerbation of pulmonary hypertension by periodontitis, and the exacerbation was potently ameliorated by both cervical lymph node excision and IFNγ neutralizing antibodies. Our study suggests a proof of concept that the combined prevention and treatment of periodontitis and pulmonary hypertension are necessary.

Diversity of bacterial community during spring phytoplankton blooms in the central Yellow Sea.

Bacterial community diversity and the effects of environmental factors on bacterial community composition during 2 spring phytoplankton blooms in the central Yellow Sea were investigated by using denaturing gradient gel electrophoresis (DGGE) and multivariate statistical analysis. The Shannon-Weaver indices (H') of bacterial diversity from samples at station B23 were higher than those at station B20. Cluster analysis based on DGGE band patterns indicated temporal variations of bacterial community at the 2 bloom stations but a vertical distribution pattern only at station B20. The predominant bacterial groups were affiliated with Alphaproteobacteria, Gammaproteobacteria, Cytophaga-Flavobacterium-Bacteroides, Deltaproteobacteria, and Actinobacteria. The effects of environmental factors on bacterial community were analyzed by canonical correspondence analysis. Bacterial community structures were significantly affected by silicate at station B20 and by Paralia sulcata and Heterocapsa spp. at station B23. From the results, phytoplankton species composition had a significant effect on bacterial community structure during phytoplankton blooms in the central Yellow Sea.

Diel variations in planktonic ciliate community structure in the northern South China Sea and tropical Western Pacific.

Though diel variations are geographically widespread phenomena among phytoplankton and zooplankton, knowledge is limited regarding diel variations in planktonic ciliate (microzooplankton) community structure. In this study, we analyzed diel variations in community structure of planktonic ciliates in the northern South China Sea (nSCS) and tropical Western Pacific (tWP). Hydrological characteristics during day and night were slightly different over both the nSCS and tWP, while ciliate average abundance at night was clearly higher than in the day in the upper 200 m. In both the nSCS and tWP, abundance proportions of large size-fraction (> 30 µm) aloricate ciliates at night were higher than in the day. While for tintinnids, abundance proportion of large lorica oral diameter at night were lower than in the day. The relationship between environmental factors and ciliate abundance pointed out that depth and temperature were main factors influencing aloricate ciliate and tintinnid in both day and night. For some dominant tintinnid species, chlorophyll a was another important factor influencing their diel vertical distribution. Our results provide fundamental data for better understanding the mechanisms of planktonic ciliate community diel variation in the tropical Western Pacific Ocean.

Insights into the structure of the pelagic microbial food web in the oligotrophic tropical Western Pacific: Examining trophic interactions and relationship with abiotic variables.

Microbial food webs (MFW) play an indispensable role in marine pelagic ecosystem, yet their composition and response to abiotic variables were poorly documented in the oligotrophic tropical Western Pacific. During winter of 2015, we conducted a survey to examine key components of MFW, including Synechococcus, Prochlorococcus, picoeukaryotes, heterotrophic prokaryotes (HP), heterotrophic/pigmented nanoflagellates and ciliates, across water column from surface to 2000 m. Each MFW component exhibited unique vertical distribution pattern, with abundance ratio varying over six and three orders of magnitude across Pico/Microplankton (1.6 ± 1.0 × 106) and Nano/Microplankton (3.2 ± 2.8 × 103), respectively. Furthermore, HP was main component for MFW in the bathypelagic (>1000 m) zone. Multivariate biota-environment analysis demonstrated that environmental variables, particularly temperature, significantly impacted MFW composition, suggesting that bottom-up control (resource availability) dominated the water column. Our study provides benchmark information for future environmental dynamics forcing on MFW in the oligotrophic tropical seas.

Seasonal and spatial variations of Synechococcus in abundance, pigment types, and genetic diversity in a temperate semi-enclosed bay.

Synechococcus is abundant and globally widespread in various marine environments. Seasonal and spatial variations in Synechococcus abundance, pigment types, and genetic diversity were investigated based on flow cytometric analysis and high-throughput sequencing of cpcBA operon (encoding phycocyanin) and rpoC1 gene (encoding RNA polymerase) in a temperate semi-enclosed bay. Synechococcus abundance exhibited seasonal variations with the highest value in summer and the lowest value in winter, which was consistent with temperature variation. Three pigment types of Synechococcus type 1, type 2, and type 3 were distinguished based on cpcBA operon, which displayed obvious variations spatially between the inner and the outer bay. Freshwater discharge and water turbidity played important roles in regulating Synechococcus pigment types. Synechococcus assemblages were phylogenetically diverse (12 different lineages) based on rpoC1 gene and dominated by three core lineages S5.1-I, S5.1-IX, and S5.2-CB5 in different seasons. Our study demonstrated that Synechococcus abundance, pigment types, and genetic diversity displayed variations seasonally and spatially by different techniques, which were mainly driven by temperature, salinity, nutrients, and turbidity. The combination of more technical means provides more information for studying Synechococcus distribution. In this study, three pigment types of Synechococcus were discriminated simultaneously by dual lasers flow cytometer for the first time.