Excitation-emission Matrix Fluorescence Spectroscopy Analysis Research Articles

Promoting effects of ferric ions on Microcystis aeruginosa growth and arsenate accumulation and reduction at different phosphorus environments

The effects of different dissolved organic phosphorus (DOP) associated with distinct iron conditions (iron deficient (dFe), ferric ions (Fe3+), and colloidal iron (CFe)) on algal growth and arsenate (As(V)) metabolism were systematically evaluated and compared in Microcystis aeruginosa. Two chemical forms of DOP (D-glucose-6-phosphate (GP) and phytic acid (PA)), as well as dissolved inorganic phosphorus (DIP), were employed as distinct phosphorus environments. The results revealed that As(V) metabolism of M. aeruginosa was more influenced by different phosphorus forms than by different iron conditions. Conversely, the release of microcystins in the media was found to be significantly more affected by the different phosphorus forms than by the iron conditions. Moreover, DOP was observed to promote arsenic (As) biotransformation, particularly the efflux of methylated As from a single algal cell, whereas DIP was found to primarily facilitate As(V) accumulation in algae. The total As metabolism amount per algal cell under PA was observed to be five times that observed under DIP and GP. The influence of iron conditions on the synthesis of algal metabolites was notable, as evidenced by the metabolites identified in algae of aliphatic (δ 1.28-1.68), humic acid-like and aromatic protein-like substances through 1H-NMR spectra and three-dimensional excitation-emission matrix fluorescence spectroscopy analysis. This impact was particularly notable at Fe3+ conditions, due to the role of Fe3+ as a micronutrient with highly bioavailable forms, which enhanced the synthesis of organic compounds in algae and promoted algal growth. Consequently, Fe3+ could inhibit As accumulation under DIP but promote it under DOP. The results obtained facilitate a more comprehensive understanding of the combined role of different phosphorus forms and iron conditions in algal bloom outbreaks and As(V) metabolism.

Extracellular proteins enhance Cupriavidus pauculus nickel tolerance and cell aggregate formation

Heavy metal-resistant bacteria secrete extracellular proteins (e-PNs). However, the role of e-PNs in heavy metal resistance remains elusive. Here Fourier Transform Infrared Spectroscopy implied that N-H, C = O and NH2-R played a crucial role in the adsorption and resistance of Ni2+ in the model organism Cuprividus pauculus 1490 (C. pauculus). Proteinase K treatment reduced Ni2+ resistance of C. pauculus underlining the essential role of e-PNs. Further three-dimension excitation-emission matrix fluorescence spectroscopy analysis demonstrated that tryptophan proteins as part of the e-PNs increased significantly with Ni2+ treatment. Proteomic and quantitative real-time polymerase chain reaction data indicated that major changes were induced in the metabolism of C. pauculus in response to Ni2+. Among those lipopolysaccharide biosynthesis, general secretion pathways, Ni2+-affiliated transporters and multidrug efflux play an essential role in Ni2+ resistance. Altogether the results provide a conceptual model for comprehending how e-PNs contribute to bacterial resistance and adsorption of Ni2+.

Biodrying of biogas residue: Maturity and microbial diversity assessment

Anaerobic digestion has developed as a mainstream method for the treatment of municipal and agricultural solid waste, which is beneficial to long-term development. Simultaneously, a large amount of biogas residue (BR) has been produced. If not correctly processed, it will pollute the environment and waste resources. However, the high moisture content of BR makes transportation and future use difficult. Biodrying can be utilized to cure BR with high moisture content, however few research has been published. The effect of a microbial agent (MA) inoculation on the biodrying of BR was investigated in this work, with a particular focus on maturation performance, material balance computation and microbial community alterations. The inoculation of MA had a significant impact on BR biodrying performance. First, MA inoculation caused 81.0% water loss, which was 46.6% higher than the control group (i.e. without MA inoculation); second, excitation-emission matrix fluorescence spectroscopy analysis revealed that MA inoculation stimulated humic compound formation; third, MA inoculation increased microbial diversity and functional bacteria abundance (e.g. Proteobacteria and Thermotogota), which may be beneficial for nitrogen migration and organic matter maturation. Therefore, biodrying through MA inoculation has the potential to be exploited in the resource use of high-moisture-content BR.

Manganese oxidation and prokaryotic community analysis in a polycaprolactone-packed aerated biofilm reactor operated under seawater conditions.

Biogenic manganese oxides (BioMnOx) have been receiving increasing attention for the removal of environmental contaminants and recovery of minor metals from water environments. However, the enrichment of heterotrophic Mn(II)-oxidizing microorganisms for BioMnOx production in the presence of fast-growing coexisting heterotrophs is challenging. In our previous work, we revealed that polycaprolactone (PCL), a biodegradable aliphatic polyester, can serve as an effective solid organic substrate to enrich Mn-oxidizing microbial communities under seawater conditions. However, marine BioMnOx-producing bioreactor systems utilizing PCL have not yet been established. Therefore, a laboratory-scale continuous-flow PCL-packed aerated biofilm (PAB) reactor was operated for 238days to evaluate its feasibility for BioMnOx production under seawater conditions. After the start-up of the reactor, the average dissolved Mn removal rates of 0.4-2.3mg/L/day, likely caused by Mn(II) oxidation, were confirmed under different influent dissolved Mn concentrations (2.5-14.0mg/L on average) and theoretical hydraulic retention time (0.19-0.77day) conditions. The 16S rRNA gene amplicon sequencing analysis suggested the presence of putative Mn(II)-oxidizing and PCL-degrading bacterial lineages in the reactor. Two highly dominant operational units (OTUs) in the packed PCL-associated biofilm were assigned to the genera Marinobacter and Pseudohoeflea, whereas the genus Lewinella and unclassified Alphaproteobacteria OTUs were highly dominant in the MnOx-containing black/dark brown precipitate-associated biofilm formed in the reactor. Excitation-emission matrix fluorescence spectroscopy analysis revealed the production of tyrosine- and tryptophane-like components, which may serve as soluble heterotrophic organic substrates in the reactor. Our findings indicate that PAB reactors are potentially applicable to BioMnOx production under seawater conditions.

Microbial electrochemistry enhanced electron transfer in lactic acid anaerobic digestion for methane production

To address the severe inhibition effect of propionic acid derived from lactic acid degradation on methane production, microbial electrodes were used to enhance electron transfer in lactic acid anaerobic digestion system. Excitation-emission matrix fluorescence spectroscopy analysis revealed that electrochemical treatment reduced the content of humic acids , which implied that intercellular electron transfer pathway changed from extracellular polymer transfer to more efficient microbial electrode transfer. The electron-producing bacteria Firmicutes with increased abundance from 51.5% to 59.7% provided more electrons on anode by degrading acetates for methanogenesis , while hydrogenotrophic methanogens Methanoculleus with increased abundance from 66.5% to 77.2% produced more methane on cathode from H 2 and CO 2 . The microorganisms formed stable biofilms on anode and cathode surfaces at 0.8 V, resulting in a 27.4% increase in methane yield to 477.1 mL CH 4 /g total volatile solids. • Electrochemistry increased methane yield from lactic acid anaerobic digestion by 27.4%. • Electron extracellular polymer transfer converted to direct electrode transfer. • Electron-producing bacteria Firmicutes boosted along with enhanced electron transfer. • Microbes formed stable biofilm on the electrode at 0.8 V to promote electron transfer.

Effect of bamboo sphere amendment on the organic matter decomposition and humification of food waste composting

The aim of this study is to examine the effect of bamboo sphere on the organic matter decomposition and humification of food waste composting. Food waste composting were carried out on four treatments, namely control (CK), 3% (T1), 6% (T2) and 9% (T3) (w/w) bamboo sphere treatments. Results showed that adding bamboo sphere facilitated the organic matter decomposition and increased the seed germination index. The number of cells in T2 treatment was always the highest during the composting process. Furthermore, the final humic substances and humic acid contents increased by 41.08% and 68.3%, respectively, in 6% bamboo sphere treatment. Fourier transform infrared and excitation-emission matrix fluorescence spectroscopy analysis revealed that adding bamboo sphere accelerated the humification of composting with more aromatic structures and humic acid-like substances. GC-MS studies revealed that the compost products of 6% bamboo sphere treatment had more ring structures, and thus enhanced the humification.

The roles of extracellular polymeric substances of Pandoraea sp. XY-2 in the removal of tetracycline.

In this study, the roles of extracellular polymeric substances (EPSs) excreted by Pandoraea sp. XY-2 in the removal of tetracycline (TC) were investigated. In the early stage, TC in the solution was mainly removed by the adsorption of EPSs, which accounted for 20% of TC. Thereafter, large amount of TC was transported into the intracellular and biodegraded. EPSs was extracted and the contents of polyprotein and polysaccharides reached their maximum values (30.84mg/g and 11.15mg/g) in the first four days. Fourier transform infrared spectroscopy analysis revealed that hydroxyl, methylidyne, methylene and amide I groups in EPSs participated in the adsorption of TC. Furthermore, three-dimensional excitation-emission matrix fluorescence spectroscopy analysis revealed that TC caused the quenching of EPSs fluorescent groups. The quenching mechanism was attributed to static quenching and protein-like substances in EPSs from Pandoraea sp. XY-2 dominated the TC adsorption process. Bioinformatic analysis of Pandoraea sp. XY-2 genome identified multiple genes involved in exopolysaccharide synthesis and EPSs formation. The insights gained in this study might provide a better understanding about the adsorption process of EPSs in tetracycline-contaminated environment.

Characteristics and sources of dissolved organic matter in a glacier in the northern Tibetan Plateau: differences between different snow categories

AbstractDissolved organic matter (DOM) in mountain glaciers is an important source of carbon for downstream aquatic systems, and its impact is expected to increase due to the increased melting rate of glaciers. We present a comprehensive study of Laohugou glacier no. 12 (LHG) at the northern edge of the Tibetan Plateau to characterize the DOM composition and sources by analyzing surface fresh snow, granular ice samples, and snow pit samples which covered a whole year cycle of 2014/15. Excitation–emission matrix fluorescence spectroscopy analysis of the DOM with parallel factor analysis (EEM-PARAFAC) identified four components, including a microbially humic-like component (C1), two protein-like components (C2 and C3) and a terrestrial humic-like component (C4). The use of Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) showed that DOM from all these samples was dominated by CHO and CHON molecular formulas, mainly corresponding to lipids and aliphatic/proteins compounds, reflecting the presence of significant amounts of microbially derived and/or deposited biogenic DOM. The molecular compositions of DOM showed more CHON compounds in granular ice than in fresh snow, likely suggesting newly formed DOM from microbes during snowmelting.

A new classification paradigm of extracellular polymeric substances (EPS) in activated sludge: Separation and characterization of exopolymers between floc level and microcolony level

Extracellular polymeric substances (EPS) play a crucial role in the formation of activated sludge flocs. However, until now, the EPS are rather classified by the method used for extraction than by a theoretical consideration of their function and composition. In this paper, a new classification paradigm of EPS was proposed, which offered a novel approach to identify the role of EPS in the formation of activated sludge flocs. The current study gave an exploration to distinguish the EPS in the floc level (extra-microcolony polymers, EMPS) and in the microcolony level (extra-cellular polymers, ECPS). It was found that cation exchange resin treatment is efficient to disintegrate the flocs for EMPS extraction, however, inefficient to disaggregate the microcolonies for ECPS harvesting. A two-steps extraction strategy (cation exchange resin treatment followed by ultrasonication-high speed centrifugation treatment) was suggested to separate these two types of EPS in activated sludge flocs and the physicochemical characteristics of EMPS and ECPS were compared. The protein/polysaccharide ratio of ECPS was higher than that of EMPS and the molecular weight of proteins in EMPS and ECPS were found to be different. The ECPS contained higher molecular weight proteins and more hydrophobic substances than the EMPS contained. The result of excitation-emission matrix fluorescence spectroscopy analysis also showed that the EMPS and the ECPS have different fluorescent expressions and the components of EMPS were more diverse than that of ECPS. All results reported herein demonstrated that two different types of exopolymers exist in the activated sludge flocs and the inter-particle forces for aggregation of activated sludge flocs are not identical between the floc level and the microcolony level. It suggested that cation bridging interactions are more crucial in floc level flocculation, while the entanglement and hydrophobic interactions are more important in microcolony level cohesion.

Bio-enhanced powder-activated carbon dynamic membrane reactor for municipal wastewater treatment

This research investigated the characteristics of bio-enhanced powder-activated carbon dynamic membrane (BPDM) reactor for municipal wastewater treatment in the laboratory-scale continuous-flow mode. The BPDM was amenable to continuous operation at high filtration fluxes in the range of 100–235L/m2h. Mean particle sizes of the BPDM increased from the top cake layer to the middle cake layer, with the largest mean particle sizes found in the bottom cake layer. The quantity of polysaccharides was greater than the quantity of proteins in the extracellular polymeric substances in the bio-enhanced powder-activated carbon mixed liquor, and the quantity of polysaccharides attached to the threads was much greater than the quantity of proteins attached to the threads of both the surface support mesh and the inner support mesh. The polysaccharides might be primarily responsible for the attachment of the BPDM to the stainless steel support mesh. Experimental results obtained via three-dimensional excitation–emission matrix fluorescence spectroscopy analysis showed that the main protein-like substances fouling the BPDM and stainless steel mesh could be identified as simple aromatic proteins, soluble microbial by-product-like materials. The amino acids in a hydrolyzed sample from the BPDM were present in larger quantities than those in the influent or the bio-enhanced powder-activated carbon mixed liquor. The BPDM was found to effectively retain the proteins.

Fouling behaviours of two membranes in a submerged membrane bioreactor for municipal wastewater treatment

Filtration performances and fouling behaviours of polyacrylonitrile (PAN) and polyvinylidene fluoride (PVDF) membranes were studied in a pilot-scale membrane bioreactor. Results showed that removable fouling was dominant for both membranes while irremovable fouling of the PVDF membrane was severer than that of the PAN membrane. The PAN membrane could reject more soluble microbial products (SMP) than the PVDF membrane due to different pore sizes. The PVDF membrane rejected more carbohydrates and fewer proteins than the PAN membrane. The mean particle size of surface foulants on the PAN membrane was smaller than that on the PVDF membrane. Gel filtration chromatography analysis indicated that the surface foulants of the PVDF membrane were comprised of larger molecular weight molecules than those of the PAN membrane. Three-dimensional excitation–emission matrix fluorescence spectroscopy analysis showed that soluble microbial by-product-like substances were the key factor causing membrane fouling of the two membranes. Hydrophobic humic-like substances played a more important role in forming irremovable fouling of the PAN membrane whereas protein-like substances were the main contributor to the irremovable fouling of the PVDF membrane. Hydrophobic fraction had the largest fouling propensity for the PAN membrane, while neutral hydrophilic fraction demonstrated the strongest fouling potential for the PVDF membrane.

Electricity generation from glucose by a Klebsiella sp. in microbial fuel cells

As electrochemically active bacteria play an important role in microbial fuel cells (MFCs), it is necessary to get a comprehensive understanding of their electrogenesis mechanisms. In this study, a new electrochemically active bacterium, Klebsiella sp. ME17, was employed into an "H" typed MFC for electrogenesis, with glucose as the electron donor. The maximum power density was 1,209 mW/m2 at a resistance of 340 Omega and the maximum current was 1.47 mA. Given the original anode medium, fresh medium, and the supernatant of the anode medium in the same MFC, respectively, the polarization curves illustrated that the strain produced mediators to promote extracellular electron transfer. The anode medium supernatant was electrochemically active, based on cyclic voltammogram, and the supernatant was very likely to contain quinone-like substances, as indicated by spectrophotometric and excitation-emission matrix fluorescence spectroscopy analysis. Further investigation on the color and ultraviolet absorbance at 254 nm of the filtered anode medium showed that the redox states of mediators strongly associated with the electricity generation states in MFCs.