Mingxue Liu

Biosorption of Strontium from Simulated Nuclear Wastewater by Scenedesmus spinosus under Culture Conditions: Adsorption and Bioaccumulation Processes and Models

Algae biosorption is an ideal wastewater treatment method when coupled with algae growth and biosorption. The adsorption and bioaccumulation of strontium from simulated nuclear wastewater by Scenedesmus spinosus were investigated in this research. One hundred mL of cultured S. spinosus cells with a dry weight of 1.0 mg in simulated nuclear wastewater were used to analyze the effects on S. spinosus cell growth as well as the adsorption and bioaccumulation characters under conditions of 25 ± 1 °C with approximately 3,000 lux illumination. The results showed that S. spinosus had a highly selective biosorption capacity for strontium, with a maximum bioremoval ratio of 76%. The adsorbed strontium ion on cell walls was approximately 90% of the total adsorbed amount; the bioaccumulation in the cytoplasm varied by approximately10%. The adsorption quantity could be described with an equilibrium isotherm. The pseudo-second-order kinetic model suggested that adsorption was the rate-limiting step of the biosorption process. A new bioaccumulation model with three parameters was proposed and could give a good fit with the experiment data. The results suggested that S. spinosus may be a potential biosorbent for the treatment of nuclear wastewater in culture conditions.

Programmed gradient descent biosorption of strontium ions by Saccaromyces cerevisiae and ashing analysis: A decrement solution for nuclide and heavy metal disposal

One of the waste disposal principles is decrement. The programmed gradient descent biosorption of strontium ions by Saccaromyces cerevisiae regarding bioremoval and ashing process for decrement were studied in present research. The results indicated that S. cerevisiae cells showed valid biosorption for strontium ions with greater than 90% bioremoval efficiency for high concentration strontium ions under batch culture conditions. The S. cerevisiae cells bioaccumulated approximately 10% of strontium ions in the cytoplasm besides adsorbing 90% strontium ions on cell wall. The programmed gradient descent biosorption presented good performance with a nearly 100% bioremoval ratio for low concentration strontium ions after 3 cycles. The ashing process resulted in a huge volume and weight reduction ratio as well as enrichment for strontium in the ash. XRD results showed that SrSO4 existed in ash. Simulated experiments proved that sulfate could adjust the precipitation of strontium ions. Finally, we proposed a technological flow process that combined the programmed gradient descent biosorption and ashing, which could yield great decrement and allow the supernatant to meet discharge standard. This technological flow process may be beneficial for nuclides and heavy metal disposal treatment in many fields.

Nano-Scale Spatial Assessment of Calcium Distribution in Coccolithophores Using Synchrotron-Based Nano-CT and STXM-NEXAFS

Calcified coccolithophores generate calcium carbonate scales around their cell surface. In light of predicted climate change and the global carbon cycle, the biomineralization ability of coccoliths has received growing interest. However, the underlying biomineralization mechanism is not yet well understood; the lack of non-invasive characterizing tools to obtain molecular level information involving biogenic processes and biomineral components remain significant challenges. In the present study, synchrotron-based Nano-computed Tomography (Nano-CT) and Scanning Transmission X-ray Microscopy-Near-edge X-ray Absorption Fine Structure Spectromicroscopy (STXM-NEXAFS) techniques were employed to identify Ca spatial distribution and investigate the compositional chemistry and distinctive features of the association between biomacromolecules and mineral components of calcite present in coccoliths. The Nano-CT results show that the coccolith scale vesicle is similar as a continuous single channel. The mature coccoliths were intracellularly distributed and immediately ejected and located at the exterior surface to form a coccoshpere. The NEXAFS spectromicroscopy results of the Ca L edge clearly demonstrate the existence of two levels of gradients spatially, indicating two distinctive forms of Ca in coccoliths: a crystalline-poor layer surrounded by a relatively crystalline-rich layer. The results show that Sr is absorbed by the coccoliths and that Sr/Ca substitution is rather homogeneous within the coccoliths. Our findings indicate that synchrotron-based STXM-NEXAFS and Nano-CT are excellent tools for the study of biominerals and provide information to clarify biomineralization mechanism.

Metabolic Influence of Psychrophilic Diatoms on Travertines at the Huanglong Natural Scenic District of China

Diatoms are a highly diversified group of algae that are widely distributed in aquatic ecosystems, and various species have different nutrient and temperature requirements for optimal growth. Here, we describe unusual psychrophilic diatoms of Cymbella in a travertine deposition environment in southwestern China in winter season. Travertine surfaces are colonized by these psychrophilic diatoms, which form biofilms of extracellular polysaccharide substances (EPS) with active metabolic activities in extremely cold conditions. The travertine in Huanglong, is a typical single crystalline calcite with anisotropic lattice distortions of unit cell parameters along axes of a and c, and this structure is suggestive of some level of metabolic mediation on mineralization. Near-edge X-ray absorption fine structure spectroscopy (NEXAFS) results further confirmed the occurrence of biogenic distortion of the crystal lattice of travertine calcite. Overall, our results imply that the metabolic influence of psychrophilic diatoms may be particularly important for promoting formation and dissolution of travertine in extremely cold environments of Huanglong. The EPS of psychrophilic diatoms will protect travertine from HCO3− etching and provide template for forming travertine when water re-flowing, in warm season.

A histone-like protein induces plasmid DNA to form liquid crystals in vitro and gene compaction in vivo.

The liquid crystalline state is a universal phenomenon involving the formation of an ordered structure via a self-assembly process that has attracted attention from numerous scientists. In this study, the dinoflagellate histone-like protein HCcp3 is shown to induce super-coiled pUC18 plasmid DNA to enter a liquid crystalline state in vitro, and the role of HCcp3 in gene condensation in vivo is also presented. The plasmid DNA (pDNA)-HCcp3 complex formed birefringent spherical particles with a semi-crystalline selected area electronic diffraction (SAED) pattern. Circular dichroism (CD) titrations of pDNA and HCcp3 were performed. Without HCcp3, pUC18 showed the characteristic B conformation. As the HCcp3 concentration increased, the 273 nm band sharply shifted to 282 nm. When the HCcp3 concentration became high, the base pair (bp)/dimer ratio fell below 42/1, and the CD spectra of the pDNA-HCcp3 complexes became similar to that of dehydrated A-form DNA. Microscopy results showed that HCcp3 compacted the super-coiled gene into a condensed state and that inclusion bodies were formed. Our results indicated that HCcp3 has significant roles in gene condensation both in vitro and in histone-less eukaryotes in vivo. The present study indicates that HCcp3 has great potential for applications in non-viral gene delivery systems, where HCcp3 may compact genetic material to form liquid crystals.

Counterion-Mediated Decompaction of Liquid Crystalline Chromosomes

Liquid crystalline phases of DNA and nucleosome core particles can be formed in vitro, indicating the crucial roles of these phases in the maintenance and compaction of genomes in vivo. In the present study, sequential levels of liquid crystalline decompaction were identified in highly purified nuclei of Karenia papilionacea in response to the gradual chelation of divalent counterions by ethylenediaminetetraacetic acid (EDTA); the decompaction was observed using polarizing light microscopy, confocal laser scanning microscopy, and transmission electron microscopy and further confirmed utilizing microcalorimetry. Nested fibrous coils in 150 nm arc-like bands of chromatin were observed in the early stages of chromosomal decompaction. The microcalorimetry spectra of isolated nuclei revealed that the dynamic processes of nuclear decompaction occurred in a nonlinear manner; in addition, an EDTA-sensitive thermal transition between 60°C-70°C, corresponding to a liquid-crystalline-phase transition of chromosomes, was found. The results suggested that nested coils of fibrous chromatin filaments are responsible for the establishment and stabilization of the liquid crystalline and birefringence features of the chromosomes of dinoflagellates. The results also indicated that positively charged divalent counterions play significant roles in modulating liquid crystalline phases to compact the chromosomes of dinoflagellates.

A high-efficiency photocatalyst, flaky anatase@natural rutile composite using one-step microwave hydrothermal synthesis

A flaky photocatalytic composite of anatase@natural rutile(A@NR) was obtained using one-step microwave hydrothermal synthesis, which was designed to overcome the low photocatalytic efficiency stemming from high electron-hole recombination and a narrow photoresponse range. The characterizations were completely elucidated using X-ray diffraction, field emission scanning electron microscopy, Brunauer Emmett Teller surface area, ultraviolet–visible diffuse reflectance spectroscopy, and photoluminescence spectra. The efficiency of A@NR in photocatalytic degradation of methyl orange was determined to be close to that of P25 under UV light and superior to that of P25 under visible light. The excellent photocatalytic activity results from the synergistic effects of substituting Fe ions, which alter the band structure, and the isomerism of anatase and natural rutile, which separates the photogenerated electron holes. The calculated apparent quantum efficiencies of 32.8 and 12.9% for A@NR, under UV and visible light irradiation, respectively, show a higher catalytic activity and a more effective photoinduced electron-hole separation in A@NR than in P25.

Contribution of surface functional groups and interface interaction to biosorption of strontium ions by Saccharomyces cerevisiae under culture conditions

Contribution of surface functional groups and detailed interface interaction for biosorption of strontium ions by Saccharomyces cerevisiae under culture conditions was investigated through chemical modification, in addition to spectroscopic and mesoscopic methods. The results showed that the biosorption ratio decreased approximately 10%, 60%, and 70% for ester group, carboxyl group, and amino group modified yeast cells, respectively. Fourier transform infrared spectroscopy and surface functional group potentiometric titration results revealed that –NH2, –COOH, and –OH were the major binding groups. The amino group displayed the greatest contribution to biosorption of strontium ions, followed by the carboxyl group and, finally, the ester group. Electrostatic interaction was the initial role and establishment of a coordination complex was the most common mechanism of interface interaction between strontium ions and the yeast cell surface. Mesoscopic analysis suggested that strontium ions may be first adsorbed on the cell surface and then transported into the cytoplasm. Transmembrane transport and the bioaccumulation model revealed that yeast cells may regulate the distribution of strontium ions through a transportation mechanism. A detailed interface interaction was discussed for S. cerevisiae biosorption of low concentration strontium ions under culture conditions. The results suggested that optimal biosorption for a microorganism relies upon enrichment of proteins and polysaccharides on the cell surface.

Calcification response of Pleurochrysis carterae to iron concentrations in batch incubations: implication for the marine biogeochemical cycle

Calcified coccolithophores, a diverse and widely distributed group of marine microalgae, produce biogenic calcite in the form of coccoliths located on the cell surface. Using batch incubations of the coccolithophorid Pleurochrysis carterae, we investigated the responses of this calcification process to iron concentrations by changing the iron supply in the initial culture media from a normal concentration to 1 ppm (parts per million), 5 ppm, and 10 ppm. Time-dependent measurements of cell population, production of inorganic carbon (coccoliths), and organic carbon (organic cellular components) showed that elevated iron supply in the growth medium of P. carterae stimulates carbon sequestration by increasing growth along enhanced photosynthetic activity and calcification. In addition, the acquired time-dependent UV-Vis and FT-IR spectra revealed that iron fertilization-enhanced coccolith calcification is accompanied by a crystalline phase transition from calcite to aragonite or amorphous phase. Our results suggest that iron concentration has a significant influence on the marine carbon cycle of coccolithophores.

Effects of riboflavin and AQS as electron shuttles on U(VI) reduction and precipitation by Shewanella putrefaciens

Understanding the mechanisms for electron shuttles (ESs) in microbial extracellular electron transfer (EET) is important in biogeochemical cycles, bioremediation applications, as well as bioenergy strategies. In this work, we adapted electrochemical techniques to probe electrochemically active and redox-active Shewanella putrefaciens. This approach detected flavins and humic-like substances of Shewanella putrefaciens, which were involved in electron transfer to the electrode. A combination of three-dimensional excitation-emission (EEM) florescence spectroscopy methods identified a mixture of riboflavin and humic-like substances in supernatants during sustained incubations. The reductive behaviour of U(VI) by Shewanella putrefaciens in the presence of riboflavin (RF) and anthraquinone-2-sulfonate (AQS) was also investigated in this study. The results indicated that RF and AQS significantly accelerated electron transfer from cells to U(VI), thus enhancing reductive U(VI). The precipitate was further evidenced by SEM, FTIR, XPS and XRD, which demonstrated that chernikovite [H2(UO2)2(PO4)2·8H2O] became the main product on the cell surface of S. putrefaciens. In a contrast, U(IV) mainly existed amorphously on the cell surface of S. putrefaciens with added RF and AQS. This work has significant implications in elucidating RF and AQS as electron shuttles that are efficient in reduction of uranium in geological environments.