Heterogeneity in metal binding by individual fluorescent components in a eutrophic algae-rich lake.

Dissolved organic matter (DOM) affects the toxicity, mobility and bioavailability of metals in aquatic environment. In this study, the interactions between two metals of environmental concern [Cu(II) and Fe(III)] with DOM in a euthrophic algae-rich lake (Lake Taihu, China), including dissolved natural organic matter (NOM) and algal extracellular polymeric substance (EPS), were studied using fluorescence excitation-emission matrix (EEM) quenching titration combined with parallel factor (PARAFAC) analysis. Obvious protein-like peaks were detected in algal EPS matrix, while both protein- and humic-like peaks can be found in NOM. PARAFAC analysis identified four fluorescent components, including one humic-, one tryptophan- and two tyrosine-like components, from 114 EEM samples. It was shown that fluorescent tyrosine- (log K(M) > 5.21) and humic-like substances (log K(M) > 4.84) in NOM fraction exhibited higher metal binding capacities than those in EPS matrix, while algal EPS was characterized with a high metal-tryptophan-like substances affinity (log K(M) > 5.08). Moreover, for the eutrophic algae-rich lakes, fluorescent tryptophan- and humic-like substances were responsible for Cu transportation, whereas the mobility of Fe would be related with the tyrosine-like substances. The results facilitate a further insight into the biogeochemical behaviors of metals in eutrophic algae-rich ecosystems as well as other related aquatic environments.

Multiple fluorescence labeling and two dimensional FTIR-13C NMR heterospectral correlation spectroscopy to characterize extracellular polymeric substances in biofilms produced during composting.

Knowledge on the structure and function of extracellular polymeric substances (EPS) in biofilms is essential for understanding biodegradation processes. Herein, a novel method based on multiple fluorescence labeling and two-dimensional (2D) FTIR-(13)C NMR heterospectral correlation spectroscopy was developed to gain insight on the composition, architecture, and function of EPS in biofilms during composting. Compared to other environmental biofilms, biofilms in the thermophilic (>55 °C) and cooling (mature) stage of composting have distinct characteristics. The results of multiple fluorescence labeling demonstrated that biofilms were distributed in clusters during the thermophilic stage (day 14), and dead cells were detected. In the mature stage (day 26), the biofilm formed a continuous layer with a thickness of approximately 20-100 µm around the compost, and recolonization of cells at the surface of the compost was easily observed. Through 2D FTIR-(13)C NMR correlation heterospectral spectroscopy, the following trend in the ease of the degradation of organic compounds was observed: heteropolysaccharides > cellulose > amide I in proteins. And proteins and cellulose showed significantly more degradation than heteropolysaccharides. In summary, the combination of multiple fluorescence labeling and 2D correlation spectroscopy is a promising approach for the characterization of EPS in biofilms.

Effects of ultrasonic pretreatment on sludge dewaterability and extracellular polymeric substances distribution in mesophilic anaerobic digestion.

Effect of ultrasonic pretreatment on sludge dewaterability was determined and the fate of extracellular polymeric substances (EPS) matrix in mesophilic anaerobic digestion after ultrasonic pretreatment was studied. Characteristics of proteins (PN), polysaccharides (PS), excitation-emission matrix (EEM) fluorescence spectroscopy and molecular weight (MW) distribution of dissolved organic matters (DOM) in different EPS fractions were evaluated. The results showed that after ultrasonic pretreatment, the normalized capillary suction time (CST) decreased from 44.4 to 11.1 (sec x L)/g total suspended solids (TSS) during anaerobic digestion, indicating that sludge dewaterability was greatly improved. The normalized CST was significantly correlated with PN concentration (R2 = 0.92, p < 0.01) and the PN/PS ratio (R2 = 0.84, p < 0.01) in the loosely bound EPS (LB-EPS) fraction. Meanwhile, the average MW of DOM in the LB-EPS and tightly bound EPS (TB-EPS) fractions also had a good correlation with the normalized CST (R2 > 0.66, p < 0.01). According to EEM fluorescence spectroscopy, tryptophan-like substances intensities in the slime, LB-EPS and TB-EPS fractions were correlated with the normalized CST. The organic matters in the EPS matrix played an important role in influencing sludge dewaterability.

In situ visualisation and characterisation of the capacity of highly reactive minerals to preserve soil organic matter (SOM) in colloids at submicron scale.

Mineral-organo associations (MOAs) are a mixture of identifiable biopolymers associated with highly reactive minerals and microorganisms. However, the in situ characterization and correlation between soil organic matter (SOM) and highly reactive Al and Fe minerals are still unclear for the lack of technologies, particularly in the long-term agricultural soil colloids at submicron scale. We combined several novel techniques, including nano-scale secondary ion mass spectrometry (NanoSIMS), X-ray absorption near edge structure (XANES) and confocal laser scanning microscopy (CLSM) to characterise the capacity of highly reactive Al and Fe minerals to preserve SOM in Ferralic Cambisol in south China. Our results demonstrated that: (1) highly reactive minerals were strongly related to SOM preservation, while SOM had a more significant line correlation with the highly reactive Al minerals than the highly reactive Fe minerals, according to the regions of interest correlation analyses using NanoSIMS; (2) allophane and ferrihydrite were the potential mineral species to determine the SOM preservation capability, which was evaluated by the X-ray photoelectron spectroscopy (XPS) and Fe K-edge XANES spectroscopy techniques; and (3) soil organic biopolymers with dominant compounds, such as proteins, polysaccharides and lipids, were distributed at the rough and clustered surface of MOAs with high chemical and spatial heterogeneity according to the CLSM observation. Our results also promoted the understanding of the roles played by the highly reactive Al and Fe minerals in the spatial distribution of soil organic biopolymers and SOM sequestration.

Towards understanding the role of extracellular polymeric substances in cyanobacterial Microcystis aggregation and mucilaginous bloom formation.

The development of mucilaginous cyanobacterial Microcystis blooms is a serious environmental and ecological problem, and information on the bloom-formation mechanism has been lacking until now. The aggregation of microbial cells was attributed to the matrix of extracellular polymeric substances (EPS). In this study, the quantitative role of EPS matrix in Microcystis aggregation and mucilaginous bloom formation was investigated. The results showed that when EPS matrix was extracted, the aggregation abilities decreased by 27.6% and 57.4% for the lab-cultured Microcystis suspension and the field-sampled Microcystis aggregates, respectively. The extended DLVO theory revealed that EPS extraction increased the energy barrier and the values of the second energy minimum, which accounted for the deteriorated aggregation. Further analysis showed an increasing attraction energy of EPS matrix during the Microcystis bloom development, whereas the predominant contribution originated from tightly bound EPS (TB-EPS) and loosely bound EPS (LB-EPS) for the lab-cultured and field-sampled Microcystis samples. The heterogeneous energy contribution of EPS subfractions was found to be associated with the variations in organic contents. Specifically, Microcystis aggregates exhibited a higher organic content of TB-EPS than of LB-EPS compared with the lab-cultured Microcystis suspension, whereas organic content in only the LB-EPS fraction for the bloom samples was significantly higher (p < 0.01) than that of the Microcystis aggregates. Based on these results, a conceptual model of EPS function was proposed in which TB-EPS plays an important role in the formation of Microcystis aggregates, after which LB-EPS contributed to the subsequent development from Microcystis aggregates to mucilaginous bloom formation.

CLAVATA3 dodecapeptide modified CdTe nanoparticles: a biocompatible quantum dot probe for in vivo labeling of plant stem cells.

CLAVATA3 (CLV3) dodecapeptides function in plant stem cell maintenance, but CLV3 function in cell-cell communication remains less clear. Here, we coupled CLV3 dodecapeptides to synthesized CdTe nanoparticles to track their bioactivity on stem cells in the root apical meristem. To achieve this, we first synthesized CdTe quantum dots (QDs) using a one-pot method, and then evaluated the cytotoxicity of the QDs in BY-2 cells. The results showed that QDs in plant cells must be used at low concentrations and for short treatment time. To make biocompatible probes to track stem cell fate, we conjugated CLV3 dodecapeptides to the QDs by the zero-coupling method; this modification greatly reduced the cytotoxicity of the QDs. Furthermore, we detected CLV3-QDs localized on the cell membrane, consistent with the known localization of CLV3. Our results indicate that using surface-modified QDs at low concentrations and for short time treatment can improve their utility for plant cell imaging.

Further insights into metal-DOM interaction: consideration of both fluorescent and non-fluorescent substances.

Information on metal binding with fluorescent substances has been widely studied. By contrast, information on metal binding with non-fluorescent substances remains lacking despite the dominance of these substances in aquatic systems. In this study, the metal binding properties of both fluorescent and non-fluorescent substances were investigated by using metal titration combined with two-dimensional correlation spectroscopy (2D-COS) analysis. The organic matters in the eutrophic algae-rich lake, including natural organic matters (NOM) and algae-induced extracellular polymeric substances (EPS), both contained fluorescent and non-fluorescent substances. The peaks in the one-dimensional spectra strongly overlapped, while 2D-COS can decompose the overlapped peaks and thus enhanced the spectral resolution. Moreover, 2D FTIR COS demonstrated that the binding susceptibility of organic ligands in both NOM and algal EPS matrices followed the order: 3400>1380>1650 cm-1, indicative the significant contribution of non-fluorescent ligands in metal binding. The modified Stern-Volmer equation also revealed a substantial metal binding potential for the non-fluorescent substances (logKM: 3.57∼4.92). As for the effects of organic ligands on metal binding, EPS was characterized with higher binding ability than NOM for both fluorescent and non-fluorescent ligands. Algae-induced EPS and the non-fluorescent substances in eutrophic algae-rich lakes should not be overlooked because of their high metal binding potential.

Investigation on extracellular polymeric substances from mucilaginous cyanobacterial blooms in eutrophic freshwater lakes.

Enhanced knowledge on extracellular polymeric substances (EPSs) of mucilaginous cyanobacterial blooms could improve our understanding of its ecological significance. This study for the first time investigated the extraction and fractionation of EPS matrix from cyanobacterial blooms in a eutrophic freshwater lake, and the changes in chemical compositions in EPS matrix during extraction were systematically investigated by two-dimensional correlation spectroscopy (2D-COS). The analyses demonstrated that organic matters were unevenly distributed among the EPS matrix, with most of organic matters being tightly bound to cyanobacterial cells. In addition, the soluble and loosely bound EPS fractions mainly consisted of proteins, while polysaccharides became the predominant compounds in the tightly bound EPS fraction. Heating extraction at 60°C for 30min led to a high EPS yield and low cell lysis when compared with other extraction methods. The 2D-COS results revealed a preferential release of OH in polysaccharides versus amide I in proteins in the initial heating; whereas further extension of heating resulted in EPS degradation, with degradation rates arranging in a decreased order from amide I, amide II, polysaccharides-like substances to polysaccharides. These results obtained would help enhance our insights into EPS characterization from cyanobacterial blooms in eutrophic lakes.

Insights into extracellular polymeric substances of cyanobacterium Microcystis aeruginosa using fractionation procedure and parallel factor analysis.

Investigations on the extracellular polymeric substances (EPS) are crucial for better understanding the growth and proliferation of cyanobacterium Microcystis aeruginosa. In this study, a combined approach of fractionation procedure and parallel factor (PARAFAC) analysis were applied to characterize the EPS of M. aeruginosa. Physicochemical analysis showed that the contents of polysaccharides in EPS matrix were higher than those of proteins, regardless of the differences in growth phases and nutritional levels in medium. Organic matters were mainly distributed in the tightly bound EPS (TB-EPS) fraction during the exponential growth phase, whereas they sharply released to the soluble EPS (SL-EPS) and loosely bound EPS (LB-EPS) fractions at the decay period. Fluorescence excitation-emission matrix (EEM) was applied to characterize the specific compositions in EPS matrix, and all the fluorescence EEM spectra collected could be successfully decomposed into a four-component model by PARAFAC analysis. Component 1 [excitation/emission (Ex/Em) = 220/340], component 2 (Ex/Em = 280/340) and component 3 [Ex/Em = (200, 220, 270)/296] were attributed to protein-like substances, while component 4 [Ex/Em = (250, 340)/438] belonged to humic-like substances. Pearson correlation analysis demonstrated that tryptophan-like substances in the LB-EPS and TB-EPS fractions were positively correlated with Microcystis growth, whereas in the SL-EPS fraction, tryptophan-like as well as humic-like substances were associated with the growth of M. aeruginosa. The scientific implication for Microcystis growth and proliferation, based on the results of fractionation procedure and EEM-PARAFAC analysis, was also presented.

Fate of biopolymers during rapeseed meal and wheat bran composting as studied by two-dimensional correlation spectroscopy in combination with multiple fluorescence labeling techniques.

Detailed knowledge of the molecular events during composting is important in improving the efficiency of this process. By combining two-dimensional Fourier transform infrared (FTIR) correlation spectroscopy and multiple fluorescent labeling, it was possible to study the degradation of biopolymers during rapeseed meal and wheat bran composting. Two-dimensional FTIR correlation spectroscopy provided structural information and was used to deconvolute overlapping bands found in the compost FTIR spectra. The degradation of biopolymers in rapeseed meal and wheat bran composts followed the sequence: cellulose, heteropolysaccharides, and proteins. Fluorescent labeling suggested that cellulose formed an intact network-like structure and the other biopolymers were embedded in the core of this structure. The sequence of degradation of biopolymers during composting was related to their distribution patterns.

Characteristics of extracellular polymeric substances (EPS) fractions from excess sludges and their effects on bioflocculability.

Extracellular polymeric substances (EPS) of biological origin are ubiquitous in excess sludges and can be applied as an underlying bioflocculant, owing to their high content of macromolecules and cations. However, low flocculating activity limits the feasibility of their practical applications. This study provides a novel EPS fractionation approach to improve their flocculability by extracting an active EPS fraction and removing the others with low flocculability. The results showed that for two excess sludges (called sludge A and sludge B), the tightly bound EPS (TB-EPS) fraction possessed a high flocculating rate to kaolin suspension compared with the other EPS fractions [i.e., supernatant, slime, and loosely bound EPS (LB-EPS) fraction] (>54.1+/-1.4% vs <7.8+/-1.6%). High bioflocculability of TB-EPS fraction could be attributable to high contents of macromolecules (330-1200 kDa) and trivalent cations (Fe(3+) and Al(3+)). Further investigation reveals that the TB-EPS fraction caused aggregation of particles by bridging and sweep flocculation.

Enhanced aerobic granulation with extracellular polymeric substances (EPS)-free pellets.

Extracellular polymeric substances (EPSs) were secreted by cells after they agglomerated into a compact aggregate. This study shows that the EPS initially embedded in seed sludge before granulation may sterically slow subsequent microbe-microbe contact, thereby delaying aerobic granulation. Three identical bioreactors were used in this study using glucose as the sole carbon and energy source. Reactor 1 (R1) was seeded with EPS-free pellets and operated in sequencing batch reactor (SBR) mode. Reactor 2 (R2) was seeded with the original sludge flocs and operated in SBR mode. Reactor 3 (R3) was seeded with EPS-free pellets and operated in continuously stirred tank reactor (CSTR) mode. Granulation occurred in R1 earlier than in R2; the granules that formed in R1 were larger and more compact than those in R2 at the same cultivation time. The few mature granules in R3 suggest that aerobic granulation can occur in a CSTR when a reactor is seeded with EPS-free pellets.