Molecular Level Characterization of Diatom-Associated Biopolymers that Bind 234Th, ²³³PA, ²¹°Pb, and 7Be in Seawater: A Case Study With Phaeodactylum tricornutum

In order to investigate the importance of biogenic silica associated biopolymers on the scavenging of radionuclides, the diatom Phaeodactylum tricornutum was incubated together with the radionuclides Th-234, Pa-233, Pb-210, and Be-7 during their growth phase. Normalized affinity coefficients were determined for the radionuclides bound with different organic compound classes (i.e., proteins, total carbohydrates, uronic acids) in extracellular (nonattached and attached exopolymeric substances), intracellular (ethylene diamine tetraacetic acid and sodium dodecyl sulfate extractable), and frustule embedded biopolymeric fractions (BF). Results indicated that radionuclides were mostly concentrated in frustule BF. Among three measured organic components, Uronic acids showed the strongest affinities to all tested radionuclides. Confirmed by spectrophotometry and two-dimensional heteronuclear single quantum coherence-nuclear magnetic resonance analyses, the frustule BF were mainly composed of carboxyl-rich, aliphatic-phosphoproteins, which were likely responsible for the strong binding of many of the radionuclides. Results from this study provide evidence for selective absorption of radionuclides with different kinds of diatom-associated biopolymers acting in concert rather than as a single compound. This clearly indicates the importance of these diatom-related biopolymers, especially frustule biopolymers, in the scavenging and fractionation of radionuclides used as particle tracers in the ocean

Effects of Engineered Nanoparticles on the Assembly of Exopolymeric Substances from Phytoplankton

The unique properties of engineered nanoparticles (ENs) that make their industrial applications so attractive simultaneously raise questions regarding their environmental safety. ENs exhibit behaviors different from bulk materials with identical chemical compositions. Though the nanotoxicity of ENs has been studied intensively, their unintended environmental impacts remain largely unknown. Herein we report experimental results of EN interactions with exopolymeric substances (EPS) from three marine phytoplankton species: Amphora sp., Ankistrodesmus angustus and Phaeodactylum tricornutum. EPS are polysaccharide-rich anionic colloid polymers released by various microorganisms that can assemble into microgels, possibly by means of hydrophobic and ionic mechanisms. Polystyrene nanoparticles (23 nm) were used in our study as model ENs. The effects of ENs on EPS assembly were monitored with dynamic laser scattering (DLS). We found that ENs can induce significant acceleration in Amphora sp. EPS assembly; after 72 hours EN-EPS aggregation reached equilibrium, forming microscopic gels of ∼4–6 µm in size. In contrast, ENs only cause moderate assembly kinetic acceleration for A. angustus and P. tricornutum EPS samples. Our results indicate that the effects of ENs on EPS assembly kinetics mainly depend on the hydrophobic interactions of ENs with EPS polymers. The cycling mechanism of EPS is complex. Nonetheless, the change of EPS assembly kinetics induced by ENs can be considered as one potential disturbance to the marine carbon cycle

Cell death, growth and physiological responses of a marine diatom to silicon and nitrogen starvation and resupply in the light and dark

The importance of phytoplankton in oceanic ecosystems and biogeochemical cycles is well recognized, but the ecological role of phytoplankton cell death, the causes, biochemistry, and the quantitative significance of cell death in the ecology of phytoplankton populations and biogeochemical cycles are not well understood. The main objective of this thesis was to determine whether nutrients (N or Si) starvation, silicate resupply and darkness promote cell death in the marine diatom, Thalassiosira weissflogii, and to quantify phytoplankton cell death by using a combination of physiological, biochemical and molecular techniques. Si deficiency has been identified as an important factor that is able to cause phytoplankton cell death and cessation of growth. This work shows that silicate resupply to a Si-starved diatom may also cause cell death which depends on the duration of Si starvation and the concentration of silicate that was resupplied. Short term (24 h) and long term (12 days) recovery from the silicate starvation in stationary or senescent phases was investigated. Both the specific algal cell death ( δb ) and growth ( μb ) rates increased and were positively correlated with concentrations of silicate resupply 24 h or two weeks after silicate was added in the stationary phase, while prolonged Si starvation resulted in a loss of cellular physiological capacity to respond to silicate resupply as there were few differences between cultures with and without silicate resupply in the senescent phase. The resupply of 100 μM silicate showed a significant increase in δb compared to that with no Si supply and the other lower Si additions (p<0.05, one-way ANOVA), which indicated that a resupply of a high silicate concentration might be detrimental or “toxic” to the cell's metabolism due to enhanced protease activities. The effect of darkness on phytoplankton cell growth and death was also addressed, with silicate resupply in the dark during stationary or senescent phases. In this study, the hypothesis that darkness and silicate resupply are important factors in determining the survival and succession of diatoms, and may protect Si-starved cells from cell death and prevent the degradation of various cellular components was experimentally examined. δb of the cultures with the 20 and 120 μM silicate resupply in the stationary phase were ~3-fold higher than those cultures with no silicate supply. However, when silicate was added in the senescent phase, δb showed no obvious difference from the no silicate supply cultures. Cultures with silicate resupply showed a higher level of the caspase-1 and -3 activities in the senescent phase than in the stationary phase. Additionally, cell death that was induced by darkness was also examined when T. weissflogii was under N or Si starvation and silicate resupply. N starvation was a more severe stress than Si starvation for the survival of diatoms. Si-starved diatom cells resulted in a higher cellular capacity for organic carbon and nitrogen, a more gradual decline in Fv/Fm, higher LAP activities and lower caspase-1 activities than N-starved cells. In darkness, nutrient-sufficient cultures showed a 3.8-fold increase in LAP activity, and a 4.2- and 1.6-fold increase in caspase-1 and -3 like activities, respectively. Darkness under the N or Si starvation enabled diatoms to prolong their viability during nutrient stress, but darkness also induced higher caspase activities

Machine learning models for fast selection of amino acids as green thermodynamic inhibitors for natural gas hydrate

Natural amino acids are non-toxic thermodynamic hydrate inhibitors without negative environmental impact, but it is difficult to accurately select the appropriate amino acid as a quick response to the operational conditions changes in the natural gas pipeline. The objective of this study was to develop mathematical models to predict the hydrate formation temperature (HFT) in presence of amino acids, capture the relationship between amino acid structure properties and their hydrate inhibition strength, and determine the optimal type and concentration to use. The HFT prediction was evaluated using multiple linear regression (MLR) and three machine learning methods including random forest (RF), M5 Rule (M5R) and support vector machine (SVM). After parameter optimization using the trial-and-error method, the coefficient of determination (R2) of the four models were 0.9328, 0.9793, 0.9795 and 0.9980, respectively. The SVM prediction of HFT outperformed other models as the root mean square error (RMSE) was 83%, 76% and 69% lower than that of the MLR, RF and M5R, respectively. Results also demonstrated that the relative importance of the amino acid concentration to the hydrate phase equilibrium was 5-fold higher than that of the intrinsic properties of the amino acid molecular. The SVM model proposed in this study served an easy-to-use tool for reliable prediction of HFT by just providing a new set of input data. This made it possible to accurately determine the minimum concentration of amino acids to be used during the gas pipeline transportation

Development and psychometric testing of the Knowledge, Attitudes and Practices (KAP) questionnaire among student Tuberculosis (TB) Patients (STBP-KAPQ) in China

Abstract Background TB outbreaking in schools is extremely complex, and presents a major challenge for public health. Understanding the knowledge, attitudes and practices among student TB patients in such settings is fundamental when it comes to decreasing future TB cases. The objective of this study was to develop a Knowledge, Attitudes and Practices Questionnaire among Student Tuberculosis Patients (STBP-KAPQ), and evaluate its psychometric properties. Methods This study was conducted in three stages: item construction, pilot testing in 10 student TB patients and psychometric testing, including reliability and validity. The item pool for the questionnaire was compiled from literature review and early individual interviews. The questionnaire items were evaluated by the Delphi method based on 12 experts. Reliability and validity were assessed using student TB patients (n = 416) and healthy students (n = 208). Reliability was examined with internal consistency reliability and test-retest reliability. Content validity was calculated by content validity index (CVI); Construct validity was examined using exploratory factor analysis (EFA) and confirmatory factor analysis (CFA); The Public Tuberculosis Knowledge, Attitudes and Practices Questionnaire (PTB-KAPQ) was applied to evaluate criterion validity; As concerning discriminant validity, T-test was performed. Results The final STBP-KAPQ consisted of three dimensions and 25 items. Cronbach’s α coefficient and intraclass correlation coefficient (ICC) was 0.817 and 0.765, respectively. Content validity index (CVI) was 0.962. Seven common factors were extracted by principal factor analysis and varimax rotation, with a cumulative contribution of 66.253%. The resulting CFA model of the STBP-KAPQ exhibited an appropriate model fit (χ2/df = 1.74, RMSEA = 0.082, CFI = 0.923, NNFI = 0.962). STBP-KAPQ and PTB-KAPQ had a strong correlation in the knowledge part, and the correlation coefficient was 0.606 (p < 0.05). Discriminant validity was supported through a significant difference between student TB patients and healthy students across all domains (p < 0.05). Conclusions An instrument, “Knowledge, Attitudes and Practices Questionnaire among Student Tuberculosis Patients (STBP-KAPQ)” was developed. Psychometric testing indicated that it had adequate validity and reliability for use in KAP researches with student TB patients in China. The new tool might help public health researchers evaluate the level of KAP in student TB patients, and it could also be used to examine the effects of TB health education

Identification of factors constraining nitrate assimilation in Lake Superior, Laurentian Great Lakes

Despite a well-documented rise in nitrate concentration over the past century, Lake Superior has retained an oligotrophic character. In part, this status results from physical attributes of the lake including low temperatures and prolonged isothermy, resulting in deep-mixing and light limitation which constrain primary production. Lake Superior is also phosphorus deficient which limits phytoplankton growth. We conducted large (20 l) volume factorial bioassay experiments to assess the influence of light and nutrients (P, Fe) on nitrate assimilation by a Lake Superior chlorophyte alga. Bioassays seeded with the chlorophyte yielded a strong response to light resulting in the rapid depletion of nitrate. High light resulted in higher activities of the key N-assimilation enzyme nitrate reductase (NR) and increased algal biomass compared to low light treatments. NR activity was highly correlated with rates of nitrate incorporation in bioassays and field surveys suggesting that NR occupies a critical place in nitrate metabolism. In bioassays, the addition of nutrients (P, Fe) only slightly increased the rate at which nitrate became depleted. Parallel trials using a luminescent cyanobacterial bioreporter confirmed the lack of response by added nutrients supporting light as an important factor in constraining nitrate assimilation by phytoplankton in the lake. © 2013 Springer Science+Business Media Dordrecht

Location optimization of silicon carbide foam packings in the unstirred packing trays reactor for the enhancement of solidified natural gas storage

Solidified natural gas technology shows significant potential for storing safely multi-fold volumes of natural gas in clathrate hydrates, but the main concern is the stochastic and slow process of hydrate nucleation making it unstable and unpredictable in practice. To overcome this limitation, methane hydrate was synthesized in a silicon carbide (SiC) ceramic foam packing trays reactor without stirring. Results suggested that the packing trays should be located near the gas-water interface instead of immersed in the aqueous phase, which decreased the induction time by about 98%. Results also highlighted the synergistic effects between the capillary wicking from the porous packings and the water suction from the initially formed hydrate clusters, which pumped water from the aqueous phase into the packings’ pores to provide an unsaturated porous environment for hydrate nucleation. It demonstrated that these two driving forces might also compete for water which became adverse to hydrate formation

Influence of pipeline steel surface on the thermal stability of methane hydrate

The thermal stability and surface adhesion of natural gas hydrate are critical for the safety of oil and gas pipelines. The roughness and hydrophobicity of the pipe surface often vary during long-distance transportation, but it remains unclear about how these variances influence the hydrate stability. In this study, twelve molecular models of solid steel pipeline surfaces with random morphology were evaluated and molecular dynamics simulations were performed to gain insights into the kinetics of methane hydrate dissociation, the nucleation and growth of gas bubbles during hydrate decomposition, and the free energy of hydrate adhesion to the solid steel surface. Results demonstrated that the stability of methane hydrate could be decreased by up to 85% by increasing the hydrophobicity of the pipe surface by 52%. The bubble nucleation site of the gas released from hydrate decomposition shifted from bulk water to the solid surface by increasing the surface hydrophobicity (: 3.73–5.74 kJ mol−1), but a highly hydrophobic surface (: 2.73 kJ mol−1) made it hard to form gas bubble on either smooth or rough surface. Moreover, the free energy of hydrate adhesion also depended on the roughness and hydrophobicity of the solid surface, while the largest energy barrier for the adhesion of methane hydrate was found on the hydrophobic surface with high roughness. The findings from this study provided theoretical support for better understanding the methane hydrate evolution principles when the surface properties of the pipe wall changed from naturally occurred events (e.g., metal corrosion) or artificial treatment (e.g. chemical coating)