A novel optical biosensor for in situ and small-scale monitoring of bacterial transport in saturated columns.

In situ monitoring techniques can provide new insight into bacterial transport after inoculating exogenous bacteria into contaminated soils for bioremediation. A real-time and non-destructive optical sensor (the optrode) was employed to monitor in situ transport of two fluorescently labelled bacteria - Green Fluorescent Protein (Gfp)-labelled, hydrophilic Pseudomonas putida and Tomato Fluorescent Protein (td)-labelled, hydrophobic Rhodococcus erythropolis, in a saturated sand column with and without rhamnolipid surfactant. In situ measurements were made at three sampling ports in the column with the optrode in two sets of column experiments. In Experiment 1, liquid samples were extracted for ex situ analyses (plate counts and fluorescence), while in Experiment 2 no liquid samples were extracted. Extracting liquid samples for ex situ analyses in Experiment 1 disturbed in situ measurements; in situ measured bacterial concentrations were lower, or a significant lag in breakthrough occurred relative to ex situ measurements. In Experiment 2, the optrode worked well in monitoring bacterial transport, which gave consistent transport parameters at each sampling port. Moreover, the optrode enabled the impact of bacterial hydrophobicity and rhamnolipid surfactant on bacterial transport to be observed. Specifically, hydrophilic P. putida was transported faster through the column than hydrophobic R. erythropolis; we infer from this result that fewer P. putida cells adsorb to sand particles than do R. erythropolis cells. The rhamnolipid surfactant enhanced the transport of both hydrophilic and hydrophobic bacteria. These two observations are consistent with Lifshitz-van der Waals forces and acid-base interactions between bacteria and sand.

Degradation of plastic waste using stimulated and naturally occurring microbial strains.

The capability of different strains derived from soil, activated sludge, farm sludge, and worms' excreta were investigated for biodegradation of high-density polyethylene, polystyrene foam, polypropylene and polyethylene terephthalate in unstimulated and stimulated conditions. Biodegradation using naturally occurring microbial strains examined in mixed (270 days) and individual (100 days) systems, while H2O2 stimulated strains were tested only in the mixed system (30 days). Penicillium raperi, Aspergillus flavus, Penicillium glaucoroseum and Pseudomonas sp. were isolated as the most plastic degrading microbes. Maximum weight loss was seen by incubation of polyethylene with Aspergillus flavus (5.5%) in unstimulated mix condition. Fourier Transform Infrared Spectroscopy (FT-IR) revealed formation of new functional groups as hydroxyl, carbonyl, alkene and alkoxy in the treated plastics. Visualisation of plastics by optical, atomic force (AFM) and electron microscopy (SEM) were also illustrated biodegradation. The derived by-products from microbial degradation was tested, and found no inhibition on microbial growth and performance.

Leachability of endocrine disrupting chemicals (EDCs) in municipal sewage sludge: Effects of EDCs interaction with dissolved organic matter.

In this study, experiments were performed to assess the significance of dissolved organic matter (DOM) on the leachability of four common EDCs, i.e., bisphenol A (BPA), 17α-ethinylestradiol (EE2), progesterone (PGT) and testosterone (TST), in municipal sewage sludge (MSS) under landfill conditions. The DOM was derived from two sources: MSS (MDOM), and natural soil represented by organic matter obtained from the Suwannee River (NDOM). Fluorescence excitation-emission matrix quenching combined with parallel factor analysis was adopted to characterize the interaction properties between the EDCs and DOM. The accumulative leachability of the target EDCs ranged from 0.09% (PGT) to 3.8% (TST). In particular, the leaching of BPA, EE2 and TST followed S-shaped curves, while PGT exhibited continuous leaching potential in untreated MSS. With the introduction of DOM, (i) the leachability of BPA and EE2 increased to 13.4% and 61.6%, respectively, whereas those of PGT and TST declined by 61.3% and 45.8%, respectively, and (ii) BPA, EE2 and PGT no longer reached leaching equilibrium but the S-shaped leaching property of TST persisted. The differential effects of MDOM and NDOM at identical concentrations on the EDCs leachability increased with curing time. BPA, EE2 and PGT quenched the MDOM fluorophores attributed to aromatic protein-like components. The fluorescence quenching of NDOM by BPA, EE2 and PGT was centered on soluble microbial by-product-like and humic-like substances. Compared with PGT, EE2 and BPA had greater capability for binding with DOM components largely via hydrophobic interactions, whereas PGT preferentially interacted with the DOM hydrophilic functionalities through specific interactions. TST had no binding capability but displayed potentials competing for sorption sites with DOM moieties. Our findings suggested that the management of MSS increased the risk of environmental contamination by EDCs for a long duration and that DOM was a useful indicator to predict the migration and transport properties of EDCs.

Analysis of time varying response on uptake patterns of Cu and Zn ions under application of ethylene diamine disuccinic acid and gibberellic acid in Lolium perenne.

The present study explores the effect of ethylene diamine disuccinic acid (EDDS) and gibberellic acid (GA) application on the phytoextraction of copper and zinc ions by Lolium perenne. When Cu was individually applied, accumulation diminished over time with little translocation from roots to shoots. In contrast, Zn accumulation and damage to roots rapidly increased over 3 days with increase in Zn translocation to shoots. Co-application of Zn to Cu amended treatments enhanced Cu concentration in shoots. For the CuEDDS application, EDDS significantly increased Cu accumulation and the damage to root increased over time, while gibberellic acid applied with Cu and Zn generally lowered metal uptake and decreased cell membrane damage. The application of EDDS and GA-EDDS, by themselves or with Cu and Zn, lowered transpiration and increased translocation, while GA increased transpiration but decreased translocation. EDDS application typically increased metal ion uptake by causing more cell damage, while GA typically lowered the damage and decreased metal uptake even though the transpiration increased over time and plant growth occurred. Furthermore, the behaviour of metal uptake changed over time and, for some treatments, the short-term and long-term response differed greatly. These results show that EDDS can be successfully used in phytoextraction of both Cu and Zn ions by Lolium perenne while GA can resist damage and protect against plant stress.

Effect of rhamnolipid on the physicochemical properties and interaction of bacteria and fungi.

Bacterial adhesion on surfaces is an essential initial step in promoting bacterial mobilization for soil bioremediation process. Modification of the cell surface is required to improve the adhesion of bacteria. The modification of physicochemical properties by rhamnolipid to Pseudomonas putida KT2442, Rhodococcus erythropolis 3586 and Aspergillus brasiliensis ATCC 16404 strains was analysed using contact angle measurements. The surface energy and total free energy of adhesion were calculated to predict the adhesion of both bacteria strains on the A. brasiliensis surface. The study of bacterial adhesion was carried out to evaluate experimental value with the theoretical results. Bacteria and fungi physicochemical properties were modified significantly when treated with rhamnolipid. The adhesion rate of P. putida improved by 16% with the addition of rhamnolipid (below 1 CMC), while the increase of rhamnolipid concentration beyond 1 CMC did not further enhance the bacterial adhesion. The addition of rhamnolipid did not affect the adhesion of R. erythropolis. A good relationship has been obtained in which water contact angle and surface energy of fungal surfaces are the major factors contributing to the bacterial adhesion. The adhesion is mainly driven by acid-base interaction. This finding provides insight to the role of physicochemical properties in controlling the bacterial adhesion on the fungal surface to enhance bacteria transport in soil bioremediation.

Effect of O2, Ni0 coatings, and iron oxide phases on pentachlorophenol dechlorination by zero-valent iron.

This study explores the zero-valent iron (ZVI) dechlorination of pentachlorophenol (PCP) and its dependence on the dissolved oxygen (O2), presence/formation of iron oxides, and presence of nickel metal on the ZVI surface. Compared to the anoxic system, PCP dechlorination was slower in the presence of O2, which is a potential competitive electron acceptor. Despite O2 presence, Ni0 deposited on the ZVI surfaces catalyzed the hydrogenation reactions and enhanced the PCP dechlorination by Ni-coated ZVI bimetal (Nic/Fe). The presence of O2 led to the formation of passivating oxides (maghemite, hematite, lepidocrocite, ferrihydrite) on the ZVI and Nic/Fe bimetallic surfaces. These passive oxides resulted in greater PCP incorporation (sorption, co-precipitation, and/or physical entrapment with the oxides) and decreased PCP dechlorination in the oxic systems compared to the anoxic systems. As received ZVI comprised of a wustite film, and in the presence of O2, only ≈ 17% PCP dechlorination observed after 25 days of exposure with tetrachlorophenol being detected as the end product. Wustite remained as the predominant oxide on as received ZVI during the 25 days of reaction with PCP under oxic and anoxic conditions. ZVI acid-pretreatment resulted in the replacement of wustite with magnetite and enhanced PCP degradation (e.g. ≈ 52% of the initial PCP dechlorinated after 25 days under oxic condition) with accumulation of mixtures of tetra-, tri-, and dichlorophenols. When the acid-washed ZVI was rinsed in NiSO4/H2SO4 solution, Ni0 deposited on the ZVI surface and all the wustite were replaced with magnetite. After 25 days of exposure to the Nic/Fe, ≈ 78% and 97% PCP dechlorination occurred under oxic and anoxic conditions, respectively, producing predominantly phenol. Wustite and magnetite are respectively electrically insulating and conducting oxides and influenced the dechlorination and H2 production. In conclusion, this study clearly demonstrates that the dissolved oxygen present in the aqueous solution decreases the PCP dechlorination and increases the PCP incorporation when using ZVI and Nic/Fe bimetallic systems. The findings provide novel insights towards deciphering and optimizing the performance of complex ZVI and bimetallic systems for PCP dechlorination in the presence of O2.

Induction of Microbial Oxidative Stress as a New Strategy to Enhance the Enzymatic Degradation of Organic Micropollutants in Synthetic Wastewater.

Organic micropollutants (OMPs) are pervasive anthropogenic contaminants of receiving waters where they can induce various adverse effects to aquatic life. Their ubiquitous environmental occurrence is primarily attributed to discharge from wastewater treatment plants due to incomplete removal by common biological wastewater treatment processes. Here, we assess a new strategy for promoting the degradation of six representative OMPs (i.e., sulfamethoxazole, carbamazepine, tylosin, atrazine, naproxen, and ibuprofen) by intentionally stimulating the production of microbial oxidoreductases to counter oxidative stress caused by oxygen perturbations. Mixed microbial cultures from a dairy farm wastewater were subjected to cyclic perturbations of dissolved oxygen (DO). A distance-based redundancy analysis was used to show that DO perturbations correlate with the abundance of Pseudomonadaceae and Rhodocyclaceae families, activities of peroxidases and cytochromes, and the degradation of OMPs. DO perturbation of 0.25 and 0.5 cycles/h led to most abundance of Pseudomonadaceae and Rhodocyclaceae families, showed higher activity of peroxidase and cytochrome, and gave largest removal of OMPs (removal of 92 ± 3% for sulfamethoxazole, 84 ± 3% for naproxen, 82 ± 3% for ibuprofen, 66 ± 2% for carbamazepine, 57 ± 15% for tylosin, and 88 ± 1% for atrazine).

Using carbon substrate as a selection pressure to enhance the potential of aerobic granular sludge microbial communities for removing contaminants of emerging concern.

The ability of aerobic granular sludge (AGS) technology to biotransform contaminants of emerging concern (CECs) is largely unknown. AGS supplemented with either acetate, 2-propanol, glycerol, or a 1:1:1 mixture of all three, were cultivated to investigate the link between carbon supplements and biotransformation of six CECs. Carbon substrate had a significant effect on the microbial community composition, as assessed by 16S rRNA gene sequence analyses. Substrate degradation requiring a larger number of catabolic reactions (i.e., glycerol and the mix) was associated with greater microbial richness. The biotransformation of CECs was 45.9% greater in communities supplemented with glycerol (60.3 ±â€¯30.2 µg L-1 VSS-1) compared to acetate (20.9 ±â€¯29.7 µg L-1 VSS-1). Database surveys of metabolic reactions indicate that microbial communities supplemented with glycerol have the greatest capacity for the degradation of aromatic compounds, while those supplemented with acetate community have the lowest.

Amendment of municipal sewage sludge with lime and mussel shell: Effects on fate of organic matter and pharmaceutically active compounds.

The deterioration in its strength from long-term degradation of organic matter and release of pharmaceutically active compounds (PhACs) have caused adverse environmental effects in municipal sewage sludge (MSS) landfill. Lime and a mixture of lime and mussel shell were employed as potential stabilization agents for MSS in this work. Their efficacy was assessed by investigating the effects on transformation of organic matter, as well as the occurrence and fate of four PhACs (fluoxetine, gemfibrozil, triclosan and carbamazepine) over 42 days. The addition of the selected agents: (i) prevented the microbial degradation of organic matter; (ii) modified the predominant functional groups of amide groups (amide I and II) and polysaccharides to deprotonated carboxylic groups and destruction of amide groups; and (iii) shifted the abundance of organic constituents from microbial by-products to humic acid-like organics with conformational changes. The measurement method provided reliable and precise results for determining PhAC concentrations in MSS with and without amendment, although matrix effects and process effects were found to affect measurement sensitivity. Available fractions of the PhACs increased in MSS with lime addition, but decreased in the presence of the mixture of lime and mussel shell due to the strong adsorption effects of the shells. The mixture of lime and mussel shell would be recommended for stabilizing MSS prior to being landfilled. However, longer term and larger scale investigation may be needed to better evaluate the applicability of lime and mussel shell for reducing the hazards and facilitating the management of MSS.

Mobility of pharmaceutical and personal care products in lime amended wastewater biosolids.

Lime amendment of biosolids can produce large quantities of hydroxyl ions and increase biosolids pH. The mobility of some pharmaceutical and personal care products (PPCPs) is closely correlated with the pH of biosolids. In this study the mobility of six PPCPs: erythromycin, fluoxetine, carbamazepine, naproxen, gemfibrozil and triclosan, was measured in unamended and lime-amended biosolids over 63days. Biosolids were equilibrated either a at pH range of 5.5-11.5 or cured over a time period up to 63days. The mobility was calculated as the proportion of PPCPs associated with the soluble phase after a given equilibrium time or a curing period. In unamended biosolids the mobility of erythromycin, fluoxetine, gemfibrozil and triclosan decreased, the mobility of naproxen increased and the mobility of carbamazepine was almost unchanged over 63days of curing. Compared to unamended biosolids, lime addition increased the mobility of erythromycin and naproxen by 21.7% and 33.8% respectively, but suppressed the mobility of carbamazepine, fluoxetine, gemfibrozil and triclosan by up to 100% after 63days. The pH influence on hydrophobicity and speciation of PPCPs correlated well with the mobility of erythromycin and fluoxetine, but only partially correlated with the mobility of the other 4 compounds over the pH of 5.5-11.5. Attenuated total reflectance Fourier transformed infrared (ATR-FTIR) and emission-excitation matrices (EEMs) provided spectroscopic evidences showing that the increases in amide and carboxylic groups, the decrease in polysaccharides, and the increases in humic substances in dissolved organic matter (DOM) may be responsible for the changes in the PPCPs' mobility. The effects of lime amendment lasted for approximately a month. The results of this work suggest that lime amendment prevents some PPCPs from being dissolved in biosolids soluble phases, but may not "lock" all PPCPs into biosolids.

Pentachlorophenol dechlorination with zero valent iron: a Raman and GCMS study of the complex role of surficial iron oxides.

The dechlorination of chlorinated organic pollutants by zero valent iron (ZVI) is an important water treatment process with a complex dependence on many variables. This complexity means that there are reported inconsistencies in terms of dechlorination with ZVI and the effect of ZVI acid treatment, which are significant and are as yet unexplained. This study aims to decipher some of this complexity by combining Raman spectroscopy with gas chromatography-mass spectrometry (GC-MS) to investigate the influence of the mineralogy of the iron oxide phases on the surface of ZVI on the reductive dechlorination of pentachlorophenol (PCP). Two electrolytic iron samples (ZVI-T and ZVI-H) were found to have quite different PCP dechlorination reactivity in batch reactors under anoxic conditions. Raman analysis of the "as-received" ZVI-T indicated the iron was mainly covered with the ferrous oxide (FeO) wustite, which is non-conducting and led to a low rate of PCP dechlorination. In contrast, the dominant oxide on the "as-received" ZVI-H was magnetite which is conducting and, compared to ZVI-T, the ZVI-H rate of PCP dechlorination was four times faster. Treating the ZVI-H sample with 1 N H2SO4 made small change to the composition of the oxide layers and also minute change to the rate of PCP dechlorination. However, treating the ZVI-T sample with H2SO4 led to the loss of wustite so that magnetite became the dominant oxide and the rate of PCP dechlorination increased to that of the ZVI-H material. In conclusion, this study clearly shows that iron oxide mineralogy can be a contributing factor to apparent inconsistencies in the literature related to ZVI performance towards dechlorination and the effect of acid treatment on ZVI reactivity.

Changes in estrogenicity and micropollutant concentrations across unit processes in a biological wastewater treatment system.

The behavior of 10 micropollutants, i.e. four estrogens (estrone, 17ß-estradiol, estriol, 17α-ethynylestradiol), carbamazepine (CBZ), sulfamethoxazole (SMX), triclosan, oxybenzone, 4-nonylphenol, and bisphenol A, was investigated in a typical domestic wastewater treatment plant. LC-MS and yeast estrogen screen bioassay were used to study the changes in micropollutants and estrogenicity across unit processes in the treatment system. Primary treatment via sedimentation showed that only 4-nonylphenol was removed, but led to no significant change in estrogenicity. Secondary treatment by the biological nitrification-dentrification process showed complete removal of oxybenzone and partial removal of the estrogens, which led to a decrease in estrogenic activity from 80 to 48 ng/L as estradiol equivalent (EEq). Ultraviolet treatment completely degraded the estrogens and triclosan, but failed to lower the concentrations of bisphenol A, SMX, and CBZ; a decrease in estrogenic activity from 48 to 5 ng/L EEq across the unit, a value that was only slightly larger than the observed EEq of 1 ng/L for the deionized control. Similarly, the anaerobic digestion of sludge completely degraded estrogens, oxybenzone, and SMX, but had no impact on bisphenol A, triclosan, and CBZ. The study emphasises the need to complement chemical analyses with estrogenic bioassays to evaluate the efficacy of waste water treatment plants.

Estrogenic activity of cylindrospermopsin and anatoxin-a and their oxidative products by FeIII-B*/H2O2.

The cyanotoxins released into waters during cyanobacterial blooms can pose serious hazards to humans and animals. Apart from their toxicological mechanisms, cyanotoxins have been shown to be involved in estrogenic activity by in vivo and in vitro assays; however, there is limited information on the change in estrogenicity of cyanotoxins following chemical oxidation. In this study, the estrogenic activity of cylindrospermopsin (CYL) and anatoxin-a (ANA) at concentrations ranging from 2.4 × 10-7 M to 2.4 × 10-12 M (CYL) and 7.1 × 10-6 M to 7.1 × 10-11 M (ANA), and after treatment by the FeIII-B*/H2O2 catalyst system, was investigated by the yeast estrogen screen (YES) assay. The results indicate that CYL and ANA acted as agonists in the YES assay (CYL logEC50 = -8.901; ANA logEC50 = -6.789), their binding affinity to estrogen receptors is associated with their intrinsic properties, including ring structures and toxicant properties. CYL and ANA were shown to simulate endocrine disrupting chemicals (EDCs) to modulate the 17ß-estradiol-induced estrogenic activity, resulting in non-monotonic dose responses. The treated CYL showed a significantly altered estrogenicity compared to the untreated CYL (T(2) = 8.168, p ≤ .05), while the estrogenicity of the treated ANA was not significantly different to the untreated ANA (T(2) = 1.295, p > .05). Intermediate products generated from CYL and ANA oxidized by FeIII-B*/H2O2 were identified using Q-Exactive Tandem Mass Spectrometry (LC-MS/MS). Treatment with FeIII-B*/H2O2 yielded open-ring by-products which likely resulted in CYL's reduced binding affinity to estrogen receptors. The insignificant change in the estrogenicity of treated ANA was possibly a result of its multiple ring structure products, which were likely able to bind to estrogen receptors. The comparisons for the estrogenicity of these cyanotoxins before and after FeIII-B*/H2O2 treatment suggest that the reductions in estrogenicity achieved by oxidation were dependent on the levels of cyanotoxins removed, as well as the estrogenicity of the degradation products. This is the first study on the change in the estrogenicity of CYL and ANA upon oxidation by FeIII-B*/H2O2, a high activity catalyst system.

Modulation of Nitrous Oxide (N2O) Accumulation by Primary Metabolites in Denitrifying Cultures Adapting to Changes in Environmental C and N.

Metabolomics provides insights into the actual physiology of cells rather than their mere "potential", as provided by genomic and transcriptomic analysis. We investigate the modulation of nitrous oxide (N2O) accumulation by intracellular metabolites in denitrifying bacteria using metabolomics and genome-based metabolic network modeling. Profiles of metabolites and their rates of production/consumption were obtained for denitrifying batch cultures under four conditions: initial COD:N ratios of 11:1 and 4:1 with and without nitrite spiking (28 mg-N L-1). Only the nitrite-spiked cultures accumulated N2O. The NO2- spiked cultures with an initial COD:N = 11:1 accumulated 3.3 ± 0.57% of the total nitrogen added as N2O and large pools of tricarboxylic acid cycle intermediates and amino acids. In comparison, the NO2- spiked cultures with COD:N = 4:1 showed significantly higher (p = 0.028) N2O accumulation (8.5.3 ± 0.9% of the total nitrogen added), which was linked to the depletion of C11-C20 fatty acids. Metabolic modeling analysis shows that at COD:N of 4:1 the denitrifying cells slowly generate electron equivalents as FADH2 through ß-oxidation of saturated fatty acids, while COD:N of 11:1 do it through the TCA cycle. When combined with NO2- shock, this prolonged the duration over which insufficient electron equivalents were available to completely reduce NOx to N2, resulting in increased N2O accumulation. Results extend the understanding of how organic carbon and nitrite loads modulate N2O accumulation in denitrification, which may contribute to further design strategies to control greenhouse gas emissions from agricultural soils or wastewater treatment systems.

Degradation of 17α-ethinylestradiol by nano zero valent iron under different pH and dissolved oxygen levels.

The catalytic properties of nanoparticles (e.g., nano zero valent iron, nZVI) have been used to effectively treat a wide range of environmental contaminants. Emerging contaminants such as endocrine disrupting chemicals (EDCs) are susceptible to degradation by nanoparticles. Despite extensive investigations, questions remain on the transformation mechanism on the nZVI surface under different environmental conditions (redox and pH). Furthermore, in terms of the large-scale requirement for nanomaterials in field applications, the effect of polymer-stabilization used by commercial vendors on the above processes is unclear. To address these factors, we investigated the degradation of a model EDC, the steroidal estrogen 17α-ethinylestradiol (EE2), by commercially sourced nZVI at pH 3, 5 and 7 under different oxygen conditions. Following the use of radical scavengers, an assessment of the EE2 transformation products shows that under nitrogen purging direct reduction of EE2 by nZVI occurred at all pHs. The radicals transforming EE2 in the absence of purging and upon air purging were similar for a given pH, but the dominant radical varied with pH. Upon air purging, EE2 was transformed by the same radical species as the non-purged system at the same respective pH, but the degradation rate was lower with more oxygen - most likely due to faster nZVI oxidation upon aeration, coupled with radical scavenging. The dominant radicals were OH at pH 3 and O2- at pH 5, and while neither radical was involved at pH 7, no conclusive inferences could be made on the actual radical involved at pH 7. Similar transformation products were observed without purging and upon air purging.

Post-denitrification using alginate beads containing organic carbon and activated sludge microorganisms.

Nitrate concentration in the final effluent is a key issue in pre-denitrification biological treatment systems. This study investigated post-denitrification with alginate beads containing immobilized activated sludge microorganisms and organic carbon source. A batch study was first performed to identify suitable carbon sources among acetate, glucose, calcium tartrate, starch and canola oil on the basis of nitrate removal and bead stability. Canola oil and starch beads exhibited significantly higher denitrification rates, greater bead stability and lower nitrite accumulation (6 mg/L and 10 mg/L, respectively). Glucose and acetate beads showed longer acclimation phases and degraded faster whereas tartrate beads had higher nitrite build-up (39 mg/L) and degraded due to brittleness. Post-denitrification with canola oil and starch beads was investigated in the final clarifier of a coupled upflow bioreactor and aerobic system treating synthetic dairy farm wastewater, and showed a denitrification efficiency of >90%. Beads faded in 12 days due to alginate degradation. Therefore, enhancement in bead strength or use of more stable nontoxic gel would be required to further prolong the treatment. Moreover, this study was conducted at laboratory scale and further research is needed for application in real systems.

Metabolic Network Modeling of Microbial Interactions in Natural and Engineered Environmental Systems.

We review approaches to characterize metabolic interactions within microbial communities using Stoichiometric Metabolic Network (SMN) models for applications in environmental and industrial biotechnology. SMN models are computational tools used to evaluate the metabolic engineering potential of various organisms. They have successfully been applied to design and optimize the microbial production of antibiotics, alcohols and amino acids by single strains. To date however, such models have been rarely applied to analyze and control the metabolism of more complex microbial communities. This is largely attributed to the diversity of microbial community functions, metabolisms, and interactions. Here, we firstly review different types of microbial interaction and describe their relevance for natural and engineered environmental processes. Next, we provide a general description of the essential methods of the SMN modeling workflow including the steps of network reconstruction, simulation through Flux Balance Analysis (FBA), experimental data gathering, and model calibration. Then we broadly describe and compare four approaches to model microbial interactions using metabolic networks, i.e., (i) lumped networks, (ii) compartment per guild networks, (iii) bi-level optimization simulations, and (iv) dynamic-SMN methods. These approaches can be used to integrate and analyze diverse microbial physiology, ecology and molecular community data. All of them (except the lumped approach) are suitable for incorporating species abundance data but so far they have been used only to model simple communities of two to eight different species. Interactions based on substrate exchange and competition can be directly modeled using the above approaches. However, interactions based on metabolic feedbacks, such as product inhibition and synthropy require extensions to current models, incorporating gene regulation and compounding accumulation mechanisms. SMN models of microbial interactions can be used to analyze complex "omics" data and to infer and optimize metabolic processes. Thereby, SMN models are suitable to capitalize on advances in high-throughput molecular and metabolic data generation. SMN models are starting to be applied to describe microbial interactions during wastewater treatment, in-situ bioremediation, microalgae blooms methanogenic fermentation, and bioplastic production. Despite their current challenges, we envisage that SMN models have future potential for the design and development of novel growth media, biochemical pathways and synthetic microbial associations.

Assessment of nitric oxide (NO) redox reactions contribution to nitrous oxide (N2 O) formation during nitrification using a multispecies metabolic network model.

Over the coming decades nitrous oxide (N2O) is expected to become a dominant greenhouse gas and atmospheric ozone depleting substance. In wastewater treatment systems, N2O is majorly produced by nitrifying microbes through biochemical reduction of nitrite (NO2(-)) and nitric oxide (NO). However it is unknown if the amount of N2O formed is affected by alternative NO redox reactions catalyzed by oxidative nitrite oxidoreductase (NirK), cytochromes (i.e., P460 [CytP460] and 554 [Cyt554 ]) and flavohemoglobins (Hmp) in ammonia- and nitrite-oxidizing bacteria (AOB and NOB, respectively). In this study, a mathematical model is developed to assess how N2O formation is affected by such alternative nitrogen redox transformations. The developed multispecies metabolic network model captures the nitrogen respiratory pathways inferred from genomes of eight AOB and NOB species. The performance of model variants, obtained as different combinations of active NO redox reactions, was assessed against nine experimental datasets for nitrifying cultures producing N2O at different concentration of electron donor and acceptor. Model predicted metabolic fluxes show that only variants that included NO oxidation to NO2(-) by CytP460 and Hmp in AOB gave statistically similar estimates to observed production rates of N2O, NO, NO2(-) and nitrate (NO3(-)), together with fractions of AOB and NOB species in biomass. Simulations showed that NO oxidation to NO2(-) decreased N2O formation by 60% without changing culture's NO2(-) production rate. Model variants including NO reduction to N2O by Cyt554 and cNor in NOB did not improve the accuracy of experimental datasets estimates, suggesting null N2O production by NOB during nitrification. Finally, the analysis shows that in nitrifying cultures transitioning from dissolved oxygen levels above 3.8 ± 0.38 to <1.5 ± 0.8 mg/L, NOB cells can oxidize the NO produced by AOB through reactions catalyzed by oxidative NirK.

Increased Uptake of Chelated Copper Ions by Lolium perenne Attributed to Amplified Membrane and Endodermal Damage.

The contributions of mechanisms by which chelators influence metal translocation to plant shoot tissues are analyzed using a combination of numerical modelling and physical experiments. The model distinguishes between apoplastic and symplastic pathways of water and solute movement. It also includes the barrier effects of the endodermis and plasma membrane. Simulations are used to assess transport pathways for free and chelated metals, identifying mechanisms involved in chelate-enhanced phytoextraction. Hypothesized transport mechanisms and parameters specific to amendment treatments are estimated, with simulated results compared to experimental data. Parameter values for each amendment treatment are estimated based on literature and experimental values, and used for model calibration and simulation of amendment influences on solute transport pathways and mechanisms. Modeling indicates that chelation alters the pathways for Cu transport. For free ions, Cu transport to leaf tissue can be described using purely apoplastic or transcellular pathways. For strong chelators (ethylenediaminetetraacetic acid (EDTA) and diethylenetriaminepentaacetic acid (DTPA)), transport by the purely apoplastic pathway is insufficient to represent measured Cu transport to leaf tissue. Consistent with experimental observations, increased membrane permeability is required for simulating translocation in EDTA and DTPA treatments. Increasing the membrane permeability is key to enhancing phytoextraction efficiency.

Lithium sorption properties of HMnO in seawater and wastewater.

The lithium concentration in seawater is 0.17 mg/L, which is very low, but the overall quantity is approximately 2.5 × 10(14) kg. Therefore, seawater, which contains a vast amount of lithium, could be a major alternative source that might supply the rising demand for lithium. This research was undertaken to evaluate the feasibility of a manganese oxide (HMnO) adsorbent, which was produced after leaching lithium from lithium manganese oxide, for lithium collection from seawater. The HMnO was synthesized and deformed to a plastic after wet blending of manganese oxide and lithium hydroxide, and subsequently, the influence of pH, sorption isotherms, sorption rates, sorption energies, and effects of the co-ions were measured. Thermodynamic parameters such as ΔG°, ΔH°, and ΔS° indicated that the nature of the lithium sorption was both spontaneous and endothermic. The used HMnO could be regenerated by washing it with an HCl solution. The results demonstrated that HMnO could be effectively used for the collection of lithium from seawater with good selectivity.