Wenjuan Song

Complexation between Hg(II) and biofilm extracellular polymeric substances: An application of fluorescence spectroscopy

The three-dimensional excitation emission matrix (EEM) fluorescence spectroscopy was employed to investigate the interaction of extracellular polymeric substances (EPS) from natural biofilm with Hg(II). The EEM spectra demonstrated that EPS with molecular weight over 14 kDa had two protein-like fluorescence peaks. The fluorescence intensity at both peaks was strongly dependent on the solution pH in the absence and presence of Hg(II), with the maximal fluorescence intensity at neutral pH. Fluorescence of both protein-like peaks was significantly quenched by Hg(II). The values of conditional stability constants (log K(a)=3.28-4.48) derived from modified Stern-Volmer equation are approximate to those for humic substances and dissolved organic matter (DOM), indicating that fluorescent components in EPS have strong binding capacity for Hg(II). Our findings suggest that EPS from biofilm is a class of important organic ligands for complexation with Hg(II) and may significantly affect the chemical forms, mobility, bioavailability and ecotoxicity of heavy metals in the aquatic environment.

Binding of dicamba to soluble and bound extracellular polymeric substances (EPS) from aerobic activated sludge: A fluorescence quenching study

Binding of dicamba to soluble EPS (SEPS) and bound EPS (BEPS) from aerobic activated sludge was investigated using fluorescence spectroscopy. Two protein-like fluorescence peaks (peak A with Ex/Em=225 nm/342-344 nm and peak B with Ex/Em=275/340-344 nm) were identified in SEPS and BEPS. Humic-like fluorescence peak C (Ex/Em=270-275 nm/450-460 nm) was only found in BEPS. Fluorescence of the peaks A and B for SEPS and peak A for BEPS were markedly quenched by dicamba at all temperatures whereas fluorescence of peaks B and C for BEPS was quenched only at 298 K. A dynamic process dominated the fluorescence quenching of peak A of both SEPS and BEPS. Fluorescence quenching of peak B and C was governed a static process. The effective quenching constants (logK(a)) were 4.725-5.293 for protein-like fluorophores of SEPS and 4.23-5.190 for protein-like fluorophores of BEPS, respectively. LogK(a) for humic-like substances was 3.85. Generally, SEPS had greater binding capacity for dicamba than BEPS, and protein-like substances bound dicamba more strongly than humic-like substances. Binding of dicamba to SEPS and BEPS was spontaneous and exothermic. Electrostatic force and hydrophobic interaction forces play a crucial role in binding of dicamba to EPS.

Nitrogen recovery from wastewater using microbial fuel cells

Nitrogen is one of major contaminants in wastewater; however, nitrogen, as bio-elements for crop growth, is the indispensable fertilizer in agriculture. In this study, two-chamber microbial fuel cells (MFCs) were first operated with microorganisms in anode chamber and potassium ferricyanide as catholyte. After being successfully startup, the two-chamber MFCs were re-constructed to three-chamber MFCs which were used to recover the NO3−-N and NH4+ -N of synthetic wastewater into valueadded nitrogenous fertilizer from cathode chamber and anode chamber, respectively. Ferric nitrate was used as the sole electron acceptor in cathode, which also was used to evaluate the NO3− -N recover efficiency in the case major anion of NO3− in cathode. The output voltage of these MFCs was about 600–700 mVat an external load of 500 Ω. About 47% NH4+ -N in anode chamber and 83% NO3− -N in cathode chamber could be recovered. Higher current density can selectively improve the recovery efficiency of both NH4+ -N and NO3− — N. The study demonstrated a nitrogen recovery process from synthetic wastewater using three-chamber MFCs.

Earthworms (Eisenia foetida, Savigny) mucus as complexing ligand for imidacloprid

Earthworms can excrete copious amounts of mucus that may affect the fraction, transport fate, and bioavailability of contaminants in soil. However, interaction of mucus with organic contaminants is still not well-known. In the present study, complexation properties of surface mucus (from the earthworm species Eisenia foetida, Savigny) with imidacloprid were investigated using fluorescence excitation emission matrix (EEM) spectroscopy. It was found that carbohydrates and proteins are major components in mucus of this species. Two fluorescent peaks belonging to protein-like substances were identified in the EEM spectrum of mucus. The protein-like fluorescence was clearly quenched by imidacloprid, indicating that the protein-like substances reacted strongly with imidacloprid. The fluorescence quenching processes was governed by a static process. The values of effective quenching constant (logKa) for these two peaks were 11.46 and 7.96, respectively, indicating that there is a strong interaction between mucus and imidacloprid and mucus–imidacloprid complexes are formed. Higher binding constants (logKb = 25.6 and 14.0) than those for heavy metals binding to dissolved organic matter or organic pollutants binding to proteins confirm the strong complexation between mucus and imidacloprid. Our study implies that earthworm surface mucus may significantly affect the fraction, toxicity, and bioavailability of organic contaminants in the soil due to its high affinity for organic contaminants.

Simultaneous removal of tetracycline hydrochloride and As(III) using poorly-crystalline manganese dioxide.

Simultaneous removal of antibiotic tetracycline hydrochloride (TC) and As(III) by poorly-crystalline Mn dioxide was investigated. TC and As(III) can be effectively oxidized and removed by MnO2. High concentrations of TC and As(III) competed with each other for oxidation or adsorption sites on MnO2 and thus affected their removal efficiency. The intermediates and products of TC after reaction with poorly-crystalline manganese dioxide were identified by LC-ESI-MS (liquid chromatography-electrospray ionization-mass spectrometry), and the decomposition pathways of TC by MnO2 were proposed. This study is helpful for understanding the importance of environmental Mn dioxides in the decontamination of combined pollution by organic pollutants and metal(loid)s.

Biosorption of Hg(II) onto goethite with extracellular polymeric substances

This study characterized the interactions of goethite, EPS from cyanobacterium Chroococcus sp. and Hg(II) using excitation emission matrix (EEM) spectra and adsorption isotherms. Three protein-like fluorescence peaks were noted to quench in the presence of Hg(II). The estimated conditional stability constant (logKa) and the binding constant (logKb) of the studied EPS-Hg(II) systems ranged 3.84-4.24 and 6.99-7.69, respectively. The proteins in EPS formed stable complex with Hg(II). The presence of proteins of Chroococcus sp. enhanced the adsorption capacity of Hg(II) on goethite; therefore, the goethite-EPS soil is a larger Hg(II) sink than goethite alone soil. Biosorption significantly affects the mobility of Hg(II) in goethite soils.

Effects of irradiation and pH on fluorescence properties and flocculation of extracellular polymeric substances from the cyanobacterium Chroococcus minutus.

Microbial extracellular polymeric substances (EPS) may flocculate or be decomposed when environmental factors change, which significantly influences nutrient cycling and transport of heavy metals. However, little information is available on the stability of EPS in natural environments. Fluorescence and flocculation properties of EPS from Chroococcus minutus under different irradiation and pH conditions were studied. Two aromatic protein-like fluorescence peaks and one tyrosine protein-like peak were identified from the excitation-emission-matrix (EEM) fluorescence spectra of EPS. UVB (ultraviolet B) and solar irradiation increased the fluorescence intensity of all the three peaks while UVC (ultraviolet C) irradiation had little effect. EPS formed unstable flocs after exposure to UV (ultraviolet) irradiation and formed stable flocs under solar irradiation. EPS were prone to flocculation under highly acidic conditions and minimal fluorescence of peaks was observed. The fluorophores in EPS were relatively stable under neutral and alkaline conditions. These findings are helpful for understanding the behavior of EPS in aquatic environments and their role in biogeochemical cycles of the elements.

Biosorption of Cu（II） to extracellular polymeric substances （EPS） from Synechoeystis sp.： a fluorescence quenching study

Biosorption of extracellular polymeric substances (EPS) from Synechocystis sp. (cyanobacterium) with Cu(II) was investigated using fluorescence spectroscopy. Three fluorescence peaks were found in the excitation-emission matrix (EEM) fluorescence spectra of EPS. Fluorescence of peak A (Ex/Em = 275/452 nm) and peak C (Ex/Em = 350/452 nm) were originated from humic-like substances and fluorescence of peak B (Ex/ Em = 275/338 nm) was attributed to protein-like substances. Fluorescence of peaks A, B, and C could be quenched by Cu(II). The effective quenching constants (lg Ka) were 2.8–5.84 for peak A, 6.4–9.24 for peak B, and 3.48–6.68 for peak C, respectively. The values of lg Ka showed a decreasing trend with increasing temperature, indicating that the quenching processes were static in nature. The binding constants (lg Kb) followed the order of peak A>peak B>peak C, implying that the humic-like substances in EPS have greater Cu(II) binding capacity than the protein-like substances. The binding site number, n, in EPS-Cu(II) complexes for peaks A, B, and C was less than 1. This suggests the negative cooperativity between multiple binding sites and the presence of more than one Cu binding site.

Biostabilization of Desert Sands Using Bacterially Induced Calcite Precipitation

ABSTRACT Sand storms have become a growing global environmental issue and there is an urgent need to explore cost-effective green technologies to stabilize the sands of desert regions. In this study, the performance of a ureolytic Bacillus sp. for stabilization of sands was evaluated. The Bacillus sp. could efficiently consolidate sand particles by hydrolysis of urea and the subsequent production of calcite and aragonite minerals. The biostabilized sands had a high resistance to erosion by a 33 m s−1 wind speed even after 12-d exposure to freeze-thaw cycles. The compressive strength of biostabilized sands was dependent on the applied cell density and concentrations of Ca2+ and urea. High cell densities, urea and Ca2+ concentrations reduced the compressive strength. The optimal cell density, Ca2+ and urea concentrations were OD600 0.4, 15 mM and 20 g L−1, respectively, when performance and cost were considered. This study shows that biostabilization of sand based on microbially induced carbonate precipitation (MICP) has potential for the prevention of sand storms and wind erosion of soil.

Different Resistance to UV-B Radiation of Extracellular Polymeric Substances of Two Cyanobacteria from Contrasting Habitats.

The effects of UV-B radiation (UVBR) on photosynthetic activity (Fv/Fm) of aquatic Synechocystis sp. and desert Chroococcus minutus and effects on composition and fluorescence property of extracellular polymeric substances (EPSs) from Synechocystis sp. and C. minutus were comparatively investigated. The desert cyanobacterium species C. minutus showed higher tolerance of PSII activity (Fv/Fm) to UVBR than the aquatic Synechocystis sp., and the inhibited PSII activity of C. minutus could be fully recovered while that of Synechocystis sp. could be partly recovered. UVBR had significant effect on the yield and biochemical composition of EPS of both species. Protein-like and humic acid-like substances were detected in EPS from Synechocystis sp., and protein-like and phenol-like fluorescent compounds were detected in EPS from C. minutus. Proteins in EPS of desert and aquatic species were significantly decomposed under UVBR, and the latter was more easily decomposed. The polysaccharides were much more resistant to UVBR than the proteins for both species. Polysaccharides of Synechocystis sp. was degraded slightly but those of C. minutus was little decomposed. The higher tolerance to UVBR of the desert cyanobacterium can be attributed to the higher resistance of its EPS to photodegradation induced by UVBR in comparison with the aquatic species.