Pd-PEPPSI-IPentAn Promoted Deactivated Amination of Aryl Chlorides with Amines under Aerobic Conditions.

We report herein a highly efficient Pd-catalyzed amination by "bulky-yet-flexible" Pd-PEPPSI-IPentAn complexes. The relationship between the N-heterocyclic carbenes (NHCs) structure and catalytic properties was discussed. Sterically hindered (hetero)aryl chlorides and a variety of aliphatic and aromatic amines can be applied in this cross-coupling, which smoothly proceeded to provide desired products. The operationally simple protocol highlights the rapid access to CAr-N bond formation under mild conditions without the exclusion of air and moisture.

Nitrogen Source Stabilization of Quorum Sensing in the Pseudomonas aeruginosa Bioaugmentation Strain SD-1.

Pseudomonas aeruginosa SD-1 is efficient at degrading aromatic compounds and can therefore contribute to the bioremediation of wastewater. P. aeruginosa uses quorum sensing (QS) to regulate the production of numerous secreted "public goods." In wastewater bioaugmentation applications, there are myriad nitrogen sources, and we queried whether various nitrogen sources impact the stabilities of both QS and the bacterial populations. In a laboratory strain of P. aeruginosa, PAO1, the absence of a nitrogen source has been shown to destabilize these populations through the emergence of QS mutant "cheaters." We tested the ability of SD-1 to grow in casein broth, a condition that requires QS for growth, when the nitrogen source with either NH4Cl, NaNO3, or NaNO2 or with no added nitrogen source. There was great variability in susceptibility to invasion by QS mutant cheaters and, by extension, the stability of the SD-1 population. When grown with NH4Cl as an extra nitrogen source, no population collapse was observed; by contrast, two-thirds of cultures grown in the presence of NaNO2 collapsed. In the populations that collapsed, the frequency of social cheaters exceeded 40%. NaNO3 and NaNO2 directly favor QS mutants of P. aeruginosa SD-1. Although the mechanism by which these nitrogen sources act is not clear, these data indicate that the metabolism of nitrogen can affect the stability of bacterial populations, an important observation for continuing industrial applications with this species.IMPORTANCE Bioaugmentation as a method to help remediate wastewater pollutant streams holds significant potential to enhance traditional methods of treatment. Addition of microbes that can catabolize organic pollutants can be an effective method to remove several toxic compounds. Such bioaugmented strains of bacteria have been shown to be susceptible to competition from the microbiota that are present in wastewater streams, limiting their potential effectiveness. Here, we show that bioaugmentation strains of bacteria might also be susceptible to invasion by social cheaters and that the nitrogen sources available in the wastewater might influence the ability of cheaters to overtake the bioaugmentation strains. Our results imply that control over the nitrogen sources in a wastewater stream or selective addition of certain nitrogen sources could help stabilize bioaugmentation strains of bacteria.

Flexible Steric Bulky Bis(Imino)acenaphthene (BIAN)-Supported N-Heterocyclic Carbene Palladium Precatalysts: Catalytic Application in Buchwald-Hartwig Amination in Air.

To achieve efficient palladium-catalyzed cross-coupling reaction under mild reaction conditions with the flexible steric bulk strategy, a series of Pd-PEPPSI (PEPPSI: pyridine-enhanced precatalyst preparation, stabilization, and initiation) complexes C1-C6 were synthesized and characterized, in which unsymmetric flexible steric bulk was introduced on the N-aryl of ancenaphthyl skeleton. These well-defined palladium complexes were found to be excellent precatalysts for Buchwald-Hartwig amination of aryl chlorides with amines in air. The electronic effect of the Pd-PEPPSI complexes and the effect of ancillary pyridine ligands were evaluated, among which complex C3 exhibited the most efficiency. It was demonstrated that the cross-coupling products were obtained in excellent yields in the presence of 0.5-0.1 mol % palladium loading. A wide range of aryl- and heteroaryl chlorides as well as various amines were compatible. The oxidative addition of aryl chlorides is revealed to be the rate-determining step in the catalytic cycle. The catalytic activity can be enhanced by introducing electron-donating groups to the Pd-PEPPSI complexes. This type of Pd-PEPPSI precatalyst showed the most efficiency reported to date for the challenging C-N cross-coupling reactions requiring no anhydrous and inert atmosphere protections, suggesting flexible steric bulk as a promising catalyst design strategy.

Aerobic degradation study of three fluoroanilines and microbial community analysis: the effects of increased fluorine substitution.

The fate of fluorinated compounds in the environment, especially polyfluorinated aromatics, is a matter of great concern. In this work, 4-Fluoroaniline (4-FA), 2,4-Difluoroanilines (2,4-DFA), and 2,3,4-Trifluoroanilines (2,3,4-TFA), were chosen as the target pollutants to study their biodegradability under aerobic conditions. The required enriched time of the mixed bacterial culture for degrading 4-FA, 2,4-DFA, and 2,3,4-TFA was 26, 51, and 165 days, respectively, which suggested that the longer enrichment time was required with the increase of fluorine substitution. At the initial concentrations of 100-200 mg L(-1), the 4-FA, 2,4-DFA, and 2,3,4-TFA could be degraded completely by the mixed bacterial culture. The maximum specific degradation rates of 4-FA, 2,4-DFA, and 2,3,4-TFA were 22.48 ± 0.55, 15.27 ± 2.04, and 8.84 ± 0.93 mg FA (g VSS h)(-1), respectively. Also, the three FAs enriched cultures showed certain potential of degrading other two FAs. The results from enzyme assay suggested the expression of meta-cleavage pathways during three FAs degradation. The denaturing gradient gel electrophoresis analysis revealed that unique bacterial communities were formed after FAs enrichment and these were principally composed of ß-Proteobacteria, Oscillatoriophycideae, δ-Proteobacteria, α-Proteobacteria, Thermales, Xanthomonadales, Deinococci, Flavobacteriia, and Actinobacteridae. The Shannon-Wiener indexes in three FAs enriched culture decreased with the increase of fluorine substitution, indicating the significant effect of fluorine substitution on the microbial diversity. These findings supply important information on the fate of three FAs under aerobic environment, and the bacterial communities in their degradation systems.

Sulfide oxidation and nitrate reduction for potential mitigation of H2S in landfills.

Because H2S emitted by landfill sites has seriously endangered human health, its removal is urgent. H2S removal by use of an autotrophic denitrification landfill biocover has been reported. In this process, nitrate-reducing and sulfide-oxidizing bacteria use a reduced sulfur source as electron donor when reducing nitrate to nitrogen gas and oxidizing sulfur compounds to sulfate. The research presented here was performed to investigate the possibility of endogenous mitigation of H2S by autotrophic denitrification of landfill waste. The sulfide oxidation bioprocess accompanied by nitrate reduction was observed in batch tests inoculated with mineralized refuse from a landfill site. Repeated supply of nitrate resulted in rapid oxidation of the sulfide, indicating that, to a substantial extent, the bioprocess may be driven by functional microbes. This bioprocess can be realized under conditions suitable for the autotrophic metabolic process, because the process occurred without addition of acetate. H2S emissions from landfill sites would be substantially reduced if this bioprocess was introduced.

Characteristics of H2S emission from aged refuse after excavation exposure.

Hydrogen sulfide (H2S(g)) emission from landfills is a widespread problem, especially when aged refuse is excavated. H2S(g) emission from aged refuse exposed to air was investigated and the results showed that large amounts of H2S(g) can be released, especially in the first few hours after excavation, when H2S(g) concentrations in air near refuse could reach 2.00 mg m(-3). Initial exposure to air did not inhibit the emission of H2S(g), as is generally assumed, but actually promoted it. The amounts of H2S(g) emitted in the first 2 d after excavation can be very dangerous, and the risks associated with the emission of H2S(g) could decrease significantly with time. Unlike a large number of sulfide existed under anaerobic conditions, the sulfide in aged municipal solid waste can be oxidized chemically to elemental sulfur (but not sulfate) under aerobic conditions, and its conversion rate was higher than 80%. Only microorganisms can oxidize the reduced sulfur species to sulfate, and the conversion rate could reach about 50%. Using appropriate techniques to enhance these chemical and biological transformations could allow the potential health risks caused by H2S(g) after refuse excavation to be largely avoided.

[Applications of biofilm in environmental pollution control and the related challenges]. / 生物膜在环境污染治理中的应用及挑战.

Biofilm has been used in environmental pollution control in recent years due to its characteristics of adsorption and biodegradation. Beyond the success of its utilization in wastewater treatment, biofilm technique has high application value in the remediation of heavy metals and organic pollutants in soils. With the extensive attention and research of emerging pollutants such as microplastics and antibiotic resistance genes (ARGs), the pivotal role of biofilm can not be overlooked. Here, we presented a comprehensive review of the structure, formation mecha-nism, population, and functional aspects of biofilm, as well as its applications and mechanisms in environmental pollution control in recent years. We emphatically discussed the removal mechanism and application progress of biofilm on heavy metals and organic pollutants. We further expounded some novel environmental challenges posed by biofilm under new circumstances, including the coexistence of various pollutants in plastisphere, the spread of ARGs, and the accumulation of pathogens. Finally, we put forward the gaps of current research and prospects for future research, especially the importance of exploring the interaction relationship and mechanism between biofilm and various pollutants. It is expected to provide theoretical basis for the development of new technology of biofilm remediation.

The possible reduction pathways of 2,4,6-trinitrotoluene (TNT) by sulfide under simulated anaerobic conditions.

To predict the final fate of 2,4,6-trinitrotoluene (TNT) and its intermediates in an anaerobic fermentative solution containing reduced sulfur species and to provide a basis for the adoption of remediation methods, we investigated the pathways of TNT (TNT(0) = 50 mg/L) reduction by Na(2)S at 30 ± 1 °C in an acetic acid-sodium bicarbonate buffer. Liquid chromatography/mass spectrometry (LC/MS) was used to identify TNT metabolites at different reaction times. The law of growth and decline of TNT and its metabolites was determined with time. The LC/MS result, combined with the physicochemical characteristics of related products and information from the literature, indicated possible TNT conversion pathways. Sulfide can initiate both nitroreduction and denitration of TNT simultaneously. Nitroreduction led to the accumulation of primary intermediates 4-hydroxylaminodinitrotoluene and 4-aminodinitrotoluene, whereas denitration resulted in the production of unidentified substances with molecular weight less than that of TNT. Also, polyreaction between the above intermediates formed many unidentified substances. Humification was concluded to be the best choice for remediation of TNT-contaminated soil and water due to the formation of intermediates with stable, intact aromatic systems. However, the denitration pathway of TNT offered the possibility of mineralization.

Dichlorido[1-(2,6-dimethyl-phenyl-imino)-1,2-diphenyl-propan-2-ol-κN,O]palladium(II) methanol monosolvate.

The title compound, [PdCl(2)(C(23)H(23)NO)]·CH(3)OH, was obtained by the reaction of 1-(2,6-dimethyl-phenyl-imino)-1,2-diphenyl-propan-2-ol and palladium chloride in methanol. The Pd atom is four-coordinated by the O atom of a tertiary alcohol, the imine N atom of the hy-droxy-limine part of the bidentate ligand and by two chloride ions, forming a nearly square-planar geometry. The complex mol-ecule and the uncoordinated methanol mol-ecule are connected via an O-H⋯O hydrogen bond.

Fouling behaviors are different at various negative potentials in electrochemical anaerobic membrane bioreactors with conductive ceramic membranes.

Membrane fouling remains a critical challenge to the practical application of anaerobic membrane bioreactor (AnMBR). To address this challenge, a conductive ceramic membrane was prepared for fouling control in AnMBR. By using the conductive membranes, the anti-fouling performances were enhanced about 3 times at potentials below -1.0 V vs Ag/AgCl compared to the conventional AnMBR. The particle size distributions and the electric field calculations suggest that such an enhancement was mainly attributed to the increased particle sizes of foulants in the supernatant and the electric field forces. Moreover, the scanning electron microscope and confocal laser scanning microscope results show that the conductive membrane at -1.0 V could increase the porosity of the gel layer on the surface, whereas the conductive membrane at -2.0 V could inhibit the activity of adhering bacteria. Surprisingly, membrane fouling of electrically-assisted AnMBR (AnEMBR) at -0.5 V was increased, which was attributed to a dense biofilm-like structure formation. Such a result is contrary to the conventional cognition that negative potential could mitigate the membrane fouling. Overall, this work supplements the understanding of the anti-fouling effects of the electric field in AnEMBR, and provides supplementary information for the engineering application of AnEMBR.

Degradation of refuse in hybrid bioreactor landfill.

OBJECTIVE: To explore the process of refuse decomposition in hybrid bioreactor landfill. METHODS: The bioreactor landfill was operated in sequencing of facultative-anaerobic and aerobic conditions with leachate recirculation, pH, COD, and ammonia in the leachate and pH, biodegradable organic matter (BDM), and cation exchange capacity (CEC) in refuse were detected. RESULTS: CEC increased gradually with the degradation of refuse, which was negatively correlated with BDM. COD and ammonia in the leachate was declined to 399.2 mg L(-1) and 20.6 mg N L(-1), respectively, during the 357-day operation. The respective concentrations of ammonia and COD were below the second and the third levels of current discharge standards in China. CONCLUSION: The refuse is relatively stable at the end of hybrid bioreactor landfill operation. Most of the readily biodegradable organic matter is mineralized in the initial phase of refuse degradation, whereas the hard-biodegradable organic matter is mainly humidified in the maturity phase of refuse degradation.

Sustainable synthesis of novel carbon microwires for the modification of a Ti mesh anode in bioelectrochemical systems.

Herein, an effective method was developed to integrate carbon microwires on Ti mesh (denoted as CM/TiM) to fabricate high-performance anodes with long-time stability in microbial fuel cell. CM/TiM was synthesized by colonizing filamentous fungi on the bread modified Ti mesh followed by carbonization, which could convert the attached mycelium into carbon microwires (denoted as CM). Benefiting from the biocompatibility and 3D interlaced structure of carbon microwires, the biomass accumulation (1027 ±â€¯83 µg cm-2) of CM/TiM have been significantly improved nearly 3 folds, thus the fabricated CM/TiM demonstrated 2-fold higher current density (12.19 ±â€¯0.07 A m-2) with significantly increased stability compared with TiM. Therefore, the present high power output, chemical stability and hydrophilic carbon microwires make CM/TiM stable, scalable and environmentally sustainable anodes in bioelectrochemical systems.

Responses of oxidation rate and microbial communities to methane in simulated landfill cover soil microcosms.

CH4 oxidation capacities and microbial community structures developed in response to the presence of CH4 were investigated in two types of landfill cover soil microcosms, waste soil (fine material in stabilized waste) and clay soil. CH4 emission fluxes were lower in the waste soil cover over the course of the experiment. After exposure to CH4 flow for 120 days, the waste soil developed CH4 oxidation capacity from 0.53 to 11.25-13.48micromol CH4gd.w.(-1)h(-1), which was ten times higher than the clay soil. The topsoils of the two soil covers were observed dried and inhibited CH4 oxidation. The maximum CH4 oxidation rate occurred at the depth of 10-20cm in the waste soil cover (the middle layer), whereas it took place mainly at the depth of 20-30cm in the clay soil cover (the bottom layer). The amounts of the phospholipid fatty acid (PLFA) biomarks 16:1omega8c and 18:1omega8c for type I and II methanotrophs, respectively, showed that type I methanotrophic bacteria predominated in the clay soil, while the type II methanotrophic bacteria were abundant in the waste soil, and the highest population in the middle layer. The results also indicated that a greater active methanotrophic community was developed in the waste soil relative to the clay soil.

Effects of in situ nitrogen removal on degradation/stabilization of MSW in bioreactor landfill.

The effects of in situ nitrogen removal on degradation of municipal solid waste (MSW) in bioreactor landfill system were investigated. The in situ nitrogen removal bioreactor landfill (NBL) consisted of fresh-refuse filled, methanogenic and nitrifying reactors was operated. The two-phase bioreactor landfill (BL) comprised of fresh-refuse filled and methanogenic reactors was used as control. The methanogenic and nitrifying reactors were all loaded with aged refuse whose placement time was 6-7 yr. Furthermore, the nitrifying reactor was in situ aerated. The results showed that the degradation of fresh-refuse was delayed and CH4 production also was reduced in the in situ nitrogen removal bioreactor landfill. It was feasible to perform in situ ammonia nitrification in aged refuse. Moreover, the efficiency of oxygen utility was high during the in situ nitrification because of the porous characteristic of aged refuse. Supplementing only 8.5mg O2 mg(-1)Nd(-1) to aged refuse could make ammonia removed completely. However, aeration did not accelerate the further stabilization of aged refuse.

In situ nitrogen removal in phase-separate bioreactor landfill.

The feasibility of in situ nitrogen removal in phase-separate bioreactor landfill was investigated. In the experiment, two sets of bioreactor landfill systems, namely conventional two-phase and in situ nitrogen removal bioreactor landfills, were operated. The in situ nitrogen removal bioreactor landfill (NBL) was comprised of a fresh-refuse filled reactor (NBLF), a methanogenic reactor (NBLM) and a nitrifying reactor (NBLN), while the two-phase bioreactor landfill (BL) used as control was comprised of a fresh-refuse filled reactor (BLF) and a methanogenic reactor (BLM). Furthermore, the methanogenic and nitrifying reactors used aged refuse as bulk agents. The results showed that in situ nitrogen removal was viable by phase-separation in the bioreactor landfill. In total 75.8 and 47.5 g of nitrogen were, respectively, removed from the NBL and the BL throughout the experiment. The methanogenic reactor used the aged refuse as medium was highly effective in removing organic matter from the fresh leachate. Furthermore, the aged refuse was also suitable to use as in situ nitrification medium. The degradation of fresh refuse was accelerated by denitrification in the initial stage (namely the initial hydrolyzing stage) despite being delayed by denitrification in a long-term operation.

Effects of temperature and hydraulic residence time (HRT) on treatment of dilute wastewater in a carrier anaerobic baffled reactor.

OBJECTIVE: To examine the effect of hydraulic residence time (HRT) on the performance and stability, to treat dilute wastewater at different operational temperatures in a carrier anaerobic baffled reactor (CABR), and hence to gain a deeper insight into microbial responses to hydraulic shocks on the base of the relationships among macroscopic performance, catabolic intermediate, and microcosmic alternation. METHODS: COD, VFAs, and microbial activity were detected with constant feed strength (300 mg/L) at different HRTs (9-18 h) and temperatures (10 degrees C-28 degrees C) in a CABR. RESULTS: The removal efficiencies declined with the decreases of HRTs and temperatures. However, the COD removal load was still higher at short HRT than at long HRT. Devastating reactor performance happened at temperature of 10 degrees C and at HRT of 9 h. HRTs had effect on the VFAs in the reactor slightly both at high and low temperatures, but the reasons differed from each other. Microbial activity was sensitive to indicate changes of environmental and operational parameters in the reactor. CONCLUSION: The CABR offers to certain extent an application to treat dilute wastewater under a hydraulic-shock at temperatures from 10 degrees C to 28 degrees C.

A common evolutionary pathway for maintaining quorum sensing in Pseudomonas aeruginosa.

In the bacterium Pseudomonas aeruginosa, the synthesis and secretion of extracellular protease is a typical cooperative behavior regulated by quorum sensing. However, this type of cooperative behavior is easily exploited by other individuals who do not synthesize public goods, which is known as the "tragedy of the commons". Here P. aeruginosa was inoculated into casein media with different nitrogen salts added. In casein broth, protease (a type of public good) is necessary for bacterial growth. After 30 days of sequential transfer, some groups propagated stably and avoided "tragedy of the commons". The evolved cooperators who continued to synthesize protease were isolated from these stable groups. By comparing the characteristics of quorum sensing in these cooperators, an identical evolutionary pattern was found. A variety of cooperative behaviors regulated by quorum sensing, such as the synthesis and secretion of protease and signals, were significantly reduced during the process of evolution. Such reductions improved the efficiency of cooperation, helping to prevent cheating. In addition, the production of pyocyanin, which is regulated by the RhlIR system, increased during the process of evolution, possibly due to its role in stabilizing the cooperation. This study contributes towards our understanding of the evolution of quorum sensing of P. aeruginosa.

Characteristics of the bioreactor landfill system using an anaerobic-aerobic process for nitrogen removal.

A sequential upflow anaerobic sludge blanket (UASB) and air-lift loop sludge blanket (ALSB) treatment was introduced into leachate recirculation to remove organic matter and ammonia from leachate in a lab-scale bioreactor landfill. The results showed that the sequential anaerobic-aerobic process might remove above 90% of COD and near to 100% of NH4+ -N from leachate under the optimum organic loading rate (OLR). The total COD removal efficiency was over 98% as the OLR increased to 6.8-7.7 g/l d, but the effluent COD concentration increased to 2.9-4.8 g/l in the UASB reactor, which inhibited the activity of nitrifying bacteria in the subsequent ALSB reactor. The NO3- -N concentration in recycled leachate reached 270 mg/l after treatment by the sequential anaerobic-aerobic process, but the landfill reactor could efficiently denitrify the nitrate. After 56 days operation, the leachate TN and NH4+ -N concentrations decreased to less than 200 mg/l in the bioreactor landfill system. The COD concentration was about 200 mg/l with less than 8 mg/l BOD in recycled leachate at the late stage. In addition, it was found that nitrate in recycled leachate had a negative effect on waste decomposition.

[Bacterial quorum sensing: Cooperation and cheating]. / 细菌群体感应"合作-欺骗"ç ”ç©¶è¿›å±•.

Quorum sensing (QS), a cell-to-cell communication, regulates a variety of social beha-viors, such as biofilm formation, public goods produce and gene horizontal transfer of bacteria. In the process of quorum sensing, public goods could be utilized by any members in the population, which was termed as cooperation. Notably, public goods also could be shared by the individuals who could not produce them, which was termed as cheating. Once cheaters come up, they possibly maintain equilibrium with cooperators, meanwhile they also possibly induce the collapse of population due to their rapid growth and shortage of public goods. Therefore, invasion of cheaters arouses wide attentions in medicine, agriculture, food science and so on regarded as a new strategy to control pathogens. In this study, based on the introduction about the theory of bacterial quorum sensing cooperation and cheating, we analyzed the factors influencing the formation and development of the relationship between cooperator and cheater. Moreover, we discussed the mechanism of stabilization in the relationship between cooperator and cheater, including kin selection, metabolic prudence, metabolic constraint (gene pleiotropy) and policing quorum sensing. Finally, some problems in current researches of quorum sensing cooperation and cheating were presented as well as the future research directions. We hoped this paper could deepen the understanding of bacterial quorum sen-sing and ecology of bacterial population.

Control of the pollution of antibiotic resistance genes in soils by quorum sensing inhibition.

To investigate whether pollution from antibiotic resistance genes (ARGs) could be affected by bacterial quorum sensing, the oxytetracycline (OTC)-containing manure was fertilized to establish the ARG-polluted soil environment. Under long-term OTC stress, substantial ARGs in the range from 10-4 to 10-3 RG/16S rRNA (resistance genes/16S rRNA) were detected in the antibiotics control (AC) group, in which OTC-containing manure was fertilized. Meanwhile, 10-6 RG/16S rRNA was detected in biological control (BC) group, in which non-OTC-containing manure was fertilized. Subsequently, two typical quorum sensing inhibitors, 4-nitropyridine N-oxide (4-NPO) and 3,4-dibromo-2H-furan-5-one (DBF), were used to treat the ARG-polluted soils. These two groups called 4-NPO treatments (NT) and DBF treatments (FT), respectively. There were no significant differences in bacterial growth and OTC degradation in NT and FT groups, compared to AC group. However, acyl-homoserine lactones such as C4-HSL, C6-HSL, and C8-HSL decreased significantly in both NT and FT groups, compared to AC group. Meanwhile, the abundance of most ARGs decreased dramatically. In FT group, the concentrations of tet(L) and tet(Q) were below the detection limits. It was demonstrated that quorum sensing inhibition could be an effective way to prevent and control the pollution of ARGs in soil.