Biogeographical and Biodiversity Patterns of Marine Planktonic Bacteria Spanning from the South China Sea across the Gulf of Bengal to the Northern Arabian Sea.

Understanding the biogeographical and biodiversity patterns of bacterial communities is essential in unraveling their responses to future environmental changes. However, the relationships between marine planktonic bacterial biodiversity and seawater chlorophyll a are largely understudied. Here, we used high-throughput sequencing to study the biodiversity patterns of marine planktonic bacteria across a broad chlorophyll a gradient spanning from the South China Sea across the Gulf of Bengal to the northern Arabian Sea. We found that the biogeographical patterns of marine planktonic bacteria complied with the scenario of homogeneous selection, with chlorophyll a concentration being the key environmental selecting variable of bacteria taxa. The relative abundance of Prochlorococcus, the SAR11 clade, the SAR116 clade, and the SAR86 clade significantly decreased in habitats with high chlorophyll a concentrations (>0.5 µg/L). Free-living bacteria (FLB) and particle-associated bacteria (PAB) displayed contrasting alpha diversity and chlorophyll a relationships with a positive linear correlation for FLB but a negative correlation for PAB. We further found that PAB had a narrower niche breadth of chlorophyll a than did FLB, with far fewer bacterial taxa being favored at higher chlorophyll a concentrations. Higher chlorophyll a concentrations were linked to the enhanced stochastic drift and reduced beta diversity of PAB but to the weakened homogeneous selection, enhanced dispersal limitation, and increased beta diversity of FLB. Taken together, our findings might broaden our knowledge about the biogeography of marine planktonic bacteria and advance the understanding of bacterial roles in predicting ecosystem functioning under future environmental changes that are derived from eutrophication. IMPORTANCE One of the long-standing interests of biogeography is to explore diversity patterns and uncover their underlying mechanisms. Despite intensive studies on the responses of eukaryotic communities to chlorophyll a concentrations, we know little about how changes in seawater chlorophyll a concentrations affect free-living bacteria (FLB) and particle-associated bacteria (PAB) diversity patterns in natural systems. Our biogeography study demonstrated that marine FLB and PAB displayed contrasting diversity and chlorophyll a relationships and exhibited completely different assembly mechanisms. Our findings broaden our knowledge about the biogeographical and biodiversity patterns of marine planktonic bacteria in nature systems and suggest that PAB and FLB should be considered independently in predicting marine ecosystem functioning under future frequent eutrophication.

Role of jellyfish in mesozooplankton community stability in a subtropical bay under the long-term impacts of temperature changes.

To understand zooplankton community changes in the context of climate change and anthropogenic disturbances, we analyzed mesozooplankton samples from four seasons in the subtropical Daya Bay, which is susceptible to perceived disturbances in the South China Sea. The zooplankton community was found to be divided into two clusters, namely the Outer-bay Cluster (OC) comprising Noctiluca scintillans, Temora turbinata, and Paracalanus spp., and the Inner-bay Cluster (IC) which was dominated by Pseudevadne tergestina, Oikopleura rufescens, and Paracalanus spp. The OC was recorded in waters with low Chl a concentrations and high salinity, coinciding with open seawater intrusion. The IC occurred in waters with high Chl a concentrations, low salinity, with terrestrial inputs from the Dan'ao River. The dominant cladoceran species has changed in spring from Penilia avirostris to Pseudevadne tergestina owing to suitable temperature conditions and the low wind speed in this region. Most of the keystone species recorded during all seasons were found to be copepods based on co-occurrence network analysis. Numbers of keystone jellyfish (cnidaria) species, such as Geryonia proboscidalis, Chelophyes contorta, and Aeginura grimaldi were significantly higher in summer than in other seasons due to a low-temperature seawater intrusion, which can result in the highest stability of community structures and affect coastal food webs and fishery resources. Our results highlight that zooplankton community succession may occur with long-term temperature changes in the subtropical Daya Bay under global climate change conditions.

Microzooplankton grazing and its key group composition in subtropical eutrophic coast of Southern China: in relation to environmental changes.

Microzooplanton play a crucial role in marine ecosystems, as they transfer matter and energy from pico- and nano-phytoplankton to mesozooplankton. In this study, we explored the seasonal variations of microzooplankton grazing derived from dilution experiments in a typical eutrophic coast of Southern China, as well as the abundance and biodiversity of its key group (ciliate), to further understand its function in the subtropical coastal food web associated with potential regulation factors. A total of 29 ciliate species belonging to 18 genera were identified, with the dominating species of Mesodinium rubrum, Strombidium globosaneum and Strombidium conicum. The spatial difference of ciliates abundance was attributed by the changes of temperature and salinity. Phytoplankton growth rate (µ) and microzooplankton grazing rate (m) ranged from 0.03 to 1.36 d-1 and 0.10 to 1.57 d-1, respectively, and both µ and m showed the highest values in summer and the lowest in winter. Moreover, microzooplankton grazing pressure on the phytoplankton standing stocks and potential primary production ranged from 10% to 79% and 58% to 471%, respectively. Our results indicated that temperature is the main environmental driving force for the seasonal changes of µ and m, and that the impacts of run-offs from the Pearl River and offshore seawater intrusion from the South China Sea are responsible for the spatial-temporal variations of phytoplankton growth and microzooplankton grazing.

Effects of terrestrial inputs and seawater intrusion on zooplankton community structure in Daya Bay, South China Sea.

Daya Bay is a eutrophic coastal region with dynamic physico-chemical conditions influenced by terrestrial inputs and seawater intrusion. Zooplankton is a crucial trophic intermediary for energy transfer and fishery resources. In this study, we assessed the distribution and composition of zooplankton in Daya Bay during summer and winter of 2015. We found that zooplankton diversity was the lowest and dominated by small copepods (Acartia spp. and Paracalanus spp.) and gelatinous Oikopleura spp. under terrestrial inputs in the Dan'ao River estuary and Aotou barbour. The highest zooplankton diversity was observed at the bay mouth that influenced by salty intruded seawater, and the dominant oceanic species (such as Euchaeta concinna and Subeucalanus subcrassus invaded into the top of the bay in winter. The dominant species in the estuary shift from Penilia avirostris to Acartia spp. compared with historical researches, indicating the effect of human activities on the succession of dominant species.

Long-term changes in summer phytoplankton communities and their influencing factors in Daya Bay, China (1991-2017).

Spatial variations in summertime phytoplankton community structure from 1991 to 2017 in Daya Bay, China were investigated in this research. The abundance of total phytoplankton and diatoms significantly increased during the study period in all regions of the bay while an increase in dinoflagellates abundance was only significant in the inner and middle bay areas. Pseudo-nitzschia spp. were overwhelmingly dominant followed by Skeletonema costatum. Ceratium furca was the dominant dinoflagellate. Overall, species diversity and evenness indices showed downward trends during the study period. Moreover, the bloom frequency of Scrippsiella trochoidea (associated with red tides) has increased rapidly since the 2000s in the inner bay. These temporal dynamics are largely explained by enhanced dissolved inorganic nitrogen (DIN) concentrations, which increased by 64.58% during 2005-2017 relative to 1991-2004, induced by human activities, along with temperature reductions and salinity increases resulting from open oceanic seawater intrusion.

The key to dinoflagellate (Noctiluca scintillans) blooming and outcompeting diatoms in winter off Pakistan, northern Arabian Sea.

The Arabian Sea is prone to large-scale algal blooms during winter monsoon annually. However, it is unclear why dinoflagellate, especially Noctiluca scintillans, replaced diatoms as the main bloom species. Based on in situ, remote sensing and numerical-model data off Pakistan, we found a stratified water with less salty, suitable temperature (~24 °C) and low-light conditions at the subsurface, as well as the organic nutrient accumulation and silicate limitation, were crucial for the growth of N. scintillans and outcompeting diatoms. The superposition of cyclonic eddy promoted N. scintillans pumping to surface and forming large-scale bloom. Subsequently, the shading effect of surface bloom caused the disappearance of subsurface chlorophyll maximum layer. This result suggests that the combined effects of nutrient structure and hydrodynamics play an important role in the prevalence of N. scintillans.

Significantly depleted 15N in suspended particulate organic matter indicating a strong influence of sewage loading in Daya Bay, China.

The influence of anthropogenic nutrient loading on the stable isotopic signatures (δ13C and δ15N) in the suspended particulate organic matter (SPOM) is still not fully understood. Water quality and the values of δ13C and δ15N in the SPOM were investigated in the surface water of Daya Bay during the spring of 2016 and 2017. The results indicated that the Dan'ao River is the main point source of nutrient pollution in Daya Bay. The δ15NPOM was very low in the Dan'ao River. The distribution pattern for this parameter in Daya Bay was determined chiefly by Dan'ao River discharge. Variations in δ15NPOM were ascribed mostly to the input of 15N-depleted DIN assimilated by the estuarine phytoplankton in Daya Bay. Extremely high NH4+ level in the river discharge should be responsible for the low δ15NPOM in the river water. The distribution of δ13CPOM in Daya Bay was regulated mainly by the input of 13C-depleted riverine SPOM. In the present study, the influence of phytoplankton growth on the δ13CPOM was not significant. Moreover, episodic rain events significantly influenced the temporal and spatial variations in water quality and isotopic signature in Daya Bay. The relatively depleted SPOM 15N in 2016 may have been correlated with the strong El Niño events of 2015-2016. Increases in the frequency and volume of rainfall associated with El Niño may have enhanced nutrient loading and the risk of algal red tide in the Daya Bay. In general, significant 15N depletion in SPOM could be the characteristic of hypereutrophic riverine waters. This study suggested that δ15NPOM may be an effective indicator of the strength of riverine nutrient loading in Daya Bay.

Prediction of Biochemical Recurrence Following Radiotherapy among Patients with Persistent PSA after Radical Prostatectomy: A Single-Center Experience.

Radiotherapy (RT) is applied in prostate cancer patients with a biochemical recurrence (BcR) after radical prostatectomy (RP). However, for the patients with persistent PSA but not undergoing the process of BcR, it remains unknown whether the application of RT can exempt them from the upcoming BcR. In this study, we identified 104 patients treated with RP who had persistent PSA level >0.1 but ≤0.2 ng/mL at 6-8 weeks after RP, of which 52 were treated with postoperative RT. Overall, 51 patients experienced BcR, among which 20 patients were treated with postoperative RT. The 5-year BCR-free survival rate of patients treated with or without postoperative RT was 96.2 and 50.0% respectively. Subgroup analysis showed that statistical differences in BcR-free survival were observed regarding to applying RT on patients with Gleason score ≤7 (p = 0.0365), with pathological tumor stage T2 or T3 (p = 0.0210 and p = 0.0073, respectively), without or with lymph node invasion (p = 0.0118 and p = 0.0303, respectively), with positive surgical margins (p < 0.0001), and with Pre-RT PSA ≤0.5 ng/mL (p < 0.0001). In multivariate analyses, PSA after surgery, Gleason score, pathological tumor stage, immediate androgen deprivation therapy after RP, and postoperative RT were significant predictors of BcR for patients with persistently elevated PSA (all p < 0.05). Finally, a coefficient-based nomogram was constructed with an excellent C-index for 5-year BCR prediction (0.76, 95% CI 0.73-0.79). These findings suggested that postoperative RT affords excellent control in BcR for patients with persistent PSA after surgery.

Characteristics of picoplankton abundances during a Thalassiosira diporocyclus bloom in the Taiwan Bank in late winter.

To understand the variations of picoplankton (Prochlorococcus, Synechococcus, picoeukaryotes, and heterotrophic bacteria) abundances during diatom bloom, the distribution of picoplankton in the Taiwan Bank, South China Sea was investigated using flow cytometry during a Thalassiosira diporocyclus bloom in March 2016. The results indicated an abrupt abundance decrease for Prochlorococcus, Synechococcus, and picoeukaryotes within the bloom area while the abundance of heterotrophic bacteria showed no significant difference between the bloom and non-bloom areas. We found two sub-groups of heterotrophic bacteria: high- and low-nucleic acid content (HNA and LNA) bacteria with HNA dominated in the bloom area whereas LNA dominated in the non-bloom area. Among the picoplankton components, HNA represented the highest (61.1%) carbon biomass in the bloom area while picoeukaryotes represented the highest (37.6%) in the non-bloom area. Our findings implied that heterotrophic bacteria, especially HNA, played an essential role during the diatom bloom.

Role of GATA-6 and Bone Morphogenetic Protein-2 in Dexamethasone-Induced Cleft Palate Formation in Institute of Cancer Research Mice.

The mechanism of cleft palate induction by dexamethasone is not fully known. Bone morphogenetic protein-2 (BMP-2) has been associated with dexamethasone-induced osteoporosis. In this study, the authors induced cleft palate models in Institute of Cancer Research mice by dexamethasone to investigate the role of BMP-2 and its transcriptional element GATA-6. The authors injected different doses of dexamethasone into pregnant mice (E13), and assessed the histology of the palatal shelf and the expression levels of BMP-2, GATA-6, and specific apoptosis-related proteins. The results showed that cleft palate formation was dependent on dexamethasone dosage, with high incidence (50.55%) at high concentration (50 mg/kg) compared with the low doses (6 mg/kg, 38.10%). Transmission electron microscopy revealed significant cellular changes of the cleft palate shelf, including loose cell connection, cellular swelling, as well as reduced extracellular matrix and mitochondria. Following exposure to dexamethasone, the apoptotic rate in the palate increased with elevated dosage. Western blotting analysis indicated that the expression levels of GATA-6 and BMP-2 were reduced, while the levels of apoptotic proteins bax and caspase-3 were increased. The results of authors' study suggested that dexamethasone-induced cleft palate formation involved apoptosis occurred in a dose-dependent manner. BMP-2 and GATA-6 mediated dexamethasone-induced cleft palate formation.