Feb 2020, Volume 14 Issue 1

Cover illustration

  • This article explains the adsorption, uptake and transmembrane transport of polycyclic aromatic hydrocarbons (PAHs) by bacteria; the regulation of membrane protein function during the transmembrane transport; and the proteomics and single cell analysis technology used to address these areas of research. There are three different regulation mechanisms for uptake, depending on the state and size of the oil droplets relative to the size of the microbial cells, which are (i) dire [Detail] ...

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    Kubra Ulucan-Altuntas, Eyup Debik

    • DDT undergoes dechlorination via Fe/Pd bimetallic nanoparticle.

    • The oxidation effect of nZVI on DDT is greatly improved when Pd is dopped.

    • The highest concentration to be treated under cancerogenesis limit was 110 mg/L.

    • The dechlorination of DDT is more like to DDE via Fe/Pd but to DDD via nZVI.

    • Degradation products concentrations are lowered via Fe/Pd when compared with nZVI.

    In this study, the bimetallic Fe/Pd nanoparticle was synthesized using the catalytic element palladium to increase the effect of nano zero valent iron (nZVI), in the light of the information obtained from our previous study, in which the nZVI synthesis method was modified. Dichlorodiphenyltrichloroethane (DDT), one of the most widely used persistent organic pollutant pesticides in the world, was investigated in terms of its degradation by Fe/Pd nanoparticles and the difference with nZVI was determined. During the study, the Fe/Pd concentration, initial DDT concentration, and contact time were selected as variables affecting the treatment. The highest possible initial DDT concentration for the treatment with Fe/Pd bimetallic nanoparticle was investigated to obtain the DDT effluent concentration below the carcinogenesis limit, 0.23 µg/L. The highest concentration that could be treated was found to be 109.95 mg/L with Fe/Pd. It was found that 44.3 min of contact time and 550 mg/L Fe/Pd concentration were needed to achieve this treatment.

    Ravikumar KVG, Debayan Ghosh, Mrudula Pulimi, Chandrasekaran Natarajan, Amitava Mukherjee

    • In situ preparation of FeNi nanoparticles on the sand via green synthesis approach.

    • Removal of tetracycline using GS-FeNi in batch and column study.

    • Both reductive degradation and sorption played crucial role the process.

    • Reusability of GS-FeNi showed about 77.39±4.3% removal on 4th cycle.

    • TC by-products after interaction showed less toxic as compared with TC.

    In this study, FeNi nanoparticles were green synthesized using Punica granatum (pomegranate) peel extract, and these nanoparticles were also formed in situ over quartz sand (GS-FeNi) for removal of tetracycline (TC). Under the optimized operating conditions, (GS-FeNi concentration: 1.5% w/v; concentration of TC: 20 mg/L; interaction period: 180 min), 99±0.2% TC removal was achieved in the batch reactor. The removal capacity was 181±1 mg/g. A detailed characterization of the sorbent and the solution before and after the interaction revealed that the removal mechanism(s) involved both the sorption and degradation of TC. The reusability of reactant was assessed for four cycles of operation, and 77±4% of TC removal was obtained in the cycle. To judge the environmental sustainability of the process, residual toxicity assay of the interacted TC solution was performed with indicator bacteria (Bacillus and Pseudomonas) and algae (Chlorella sp.), which confirmed a substantial decrease in the toxicity. The continuous column studies were undertaken in the packed bed reactors using GS-FeNi. Employing the optimized conditions, quite high removal efficiency (978±5 mg/g) was obtained in the columns. The application of GS-FeNi for antibiotic removal was further evaluated in lake water, tap water, and ground water spiked with TC, and the removal capacity achieved was found to be 781±5, 712±5, and 687±3 mg/g, respectively. This work can pave the way for treatment of antibiotics and other pollutants in the reactors using novel green composites prepared from fruit wastes.

    Kanha Gupta, Nitin Khandelwal, Gopala Krishna Darbha

    • Eco-friendly IONPs were synthesized through solvothermal method.

    • IONPs show very high removal efficiency for CeO2 NPs i.e. 688 mg/g.

    • Removal was >90% in all synthetic and real water samples.

    • >80% recovery of CeO2 NPs through sonication confirms reusability of IONPs.

    Increasing applications of metal oxide nanoparticles and their release in the natural environment is a serious concern due to their toxic nature. Therefore, it is essential to have eco-friendly solutions for the remediation of toxic metal oxides in an aqueous environment. In the present study, eco-friendly Iron Oxide Nanoparticles (IONPs) are synthesized using solvothermal technique and successfully characterized using scanning and transmission electron microscopy (SEM and TEM respectively) and powder X-Ray diffraction (PXRD). These IONPs were further utilized for the remediation of toxic metal oxide nanoparticle, i.e., CeO2. Sorption experiments were also performed in complex aqueous solutions and real water samples to check its applicability in the natural environment. Reusability study was performed to show cost-effectiveness. Results show that these 200 nm-sized spherical IONPs, as revealed by SEM and TEM analysis, were magnetite (Fe3O4) and contained short-range crystallinity as confirmed from XRD spectra. Sorption experiments show that the composite follows the pseudo-second-order kinetic model. Further R2>0.99 for Langmuir sorption isotherm suggests chemisorption as probable removal mechanism with monolayer sorption of CeO2 NPs on IONP. More than 80% recovery of adsorbed CeO2 NPs through ultrasonication and magnetic separation of reaction precipitate confirms reusability of IONPs. Obtained removal % of CeO2 in various synthetic and real water samples was>90% signifying that IONPs are candidate adsorbent for the removal and recovery of toxic metal oxide nanoparticles from contaminated environmental water samples.

    Yiquan Wu, Ying Xu, Ningyi Zhou

    Mycobacterium vanbaalenii PYR-1 utilizes PAHs at different rates.

    • Both NidA3B3 and FNidA3B3 catalyze high-molecular-weight PAHs dihydroxylation.

    • NidA3B3 shows an enhanced activity with an endogenous electron transport chain.

    • FNidA3B3 has an enhanced activity by 50% approximately compared with NidA3B3.

    • FNidA3B3/NidA3B3 and NidAB in the same strain come from different ancestors.

    NidA3B3 is a terminal dioxygenase whose favorable substrates are high-molecular-weight polyaromatic hydrocarbons (PAHs) from Mycobacterium vanbaalenii PYR-1, a powerful PAHs degradation strain. NidA3B3 was reported to incorporate a dioxygen into the benzene ring of PAHs when equipped with an exogenous electron transport chain components PhdCD from Nocardioides sp. strain KP7 by biotransformation, but this enzyme system was not particularly efficient. In this study, strain PYR-1 was confirmed to utilize four different PAHs at different growth rates. When PhtAcAd, an endogenous electron transport chain of a phthalate dioxygenase system, was substituted for PhdCD to couple with NidA3B3, the specific activity to convert phenanthrene by strain BL21(DE3) [pNidA3B3-PhAcAd] was 0.15±0.03 U/mg, but the specific activity of strain BL21(DE3) [pNidA3B3-PhdCD] was only 0.025±0.006 U/mg. In addition, FNidA3, encoded by a newly defined ORF, has a prolonged 19-amino acid sequence at the N-terminal compared with NidA3. FNidA3B3 increased the activity by 50% approximately than NidA3B3 when using PhtAcAd. Components of the electron transport chain PhtAc and PhtAd were purified and characterized. The Km, kcat, kcat/Km values of the PhtAd were 123±26.9 M, 503±49.9 min1, 4.1 M1·min1, respectively. And the Km, kcat, kcat/Km values of the ferredoxin PhtAc were 52.5±9.7 M, 3.8±0.19 min1 and 0.07 M1·min1, respectively. Basing on the phylogenetic analysis, NidA3/FNidA3 were far from its isoenzyme NidA from the same strain. Combining their primary differences of transcriptional pattern in vivo, it indicated that the functionally similar Rieske dioxygenases NidA3B3/FNidA3B3 and NidAB might originate from different ancestors.

    Chao Yang, Wenjun Sun, Xiuwei Ao

    • Long amplicon is more effective to test DNA damage induced by UV.

    • ATP in bacteria does not degrade instantly but does eventually after UV exposure.

    • After medium pressure UV exposure, ATP degraded faster.

    The efficacy of ultraviolet (UV) disinfection has been validated in numerous studies by using culture-based methods. However, the discovery of viable but non-culturable bacteria has necessitated the investigation of UV disinfection based on bacterial viability parameters. We used quantitative polymerase chain reaction (qPCR) to investigate DNA damage and evaluated adenosine triphosphate (ATP) to indicate bacterial viability. The results of qPCR effectively showed the DNA damage induced by UV when using longer gene amplicons, in that sufficiently long amplicons of both 16S and gadA indicated that the UV induced DNA damages. The copy concentrations of the long amplicons of 16S and gadA decreased by 2.38 log/mL and 1.88 log/mL, respectively, after exposure to 40 mJ/cm2 low-pressure UV. After UV exposure, the ATP level in the bacteria did not decrease instantly. Instead it decreased gradually at a rate that was positively related to the UV fluence. For low-pressure UV, this rate of decrease was slow, but for medium pressure UV, this rate of decrease was relatively high when the UV fluence reached 40 mJ/cm2. At the same UV fluence, the ATP level in the bacteria decreased at a faster rate after exposure to medium-pressure UV.

    Songwei Lin, Yaobin Lu, Bo Ye, Cuiping Zeng, Guangli Liu, Jieling Li, Haiping Luo, Renduo Zhang

    • MEDCC combined with Fenton process was developed to treat real pesticide wastewater.

    • Pesticide removal was attributable to desalination in the MEDCC.

    • High COD removal was attributable to organic distributions in different chambers.

    The combination of the microbial electrolysis desalination and chemical-production cell (MEDCC) and Fenton process for the pesticide wastewater treatment was investigate in this study. Real wastewater with several toxic pesticides, 1633 mg/L COD, and 200 in chromaticity was used for the investigation. Results showed that desalination in the desalination chamber of MEDCC reached 78%. Organics with low molecular weights in the desalination chamber could be removed from the desalination chamber, resulting in 28% and 23% of the total COD in the acid-production and cathode chambers, respectively. The desalination in the desalination chamber and organic transfer contributed to removal of pesticides (e.g., triadimefon), which could not be removed with other methods, and of the organics with low molecular weights. The COD in the effluent of the MEDCC combined the Fenton process was much lower than that in the perixo-coagulaiton process (<150 vs. 555 mg/L). The combined method consumed much less energy and acid for the pH adjustment than that the Fenton.

    Ling Huang, Syed Bilal Shah, Haiyang Hu, Ping Xu, Hongzhi Tang

    • Bioremediation is the most cost-effective approach for degradation of HBCDs.

    • Bacteria or bacterial consortia are used in the cases of bio-augmentation.

    • Microbes combined with phytoremediation increase the remediation efficiency.

    Hexabromocyclododecanes (HBCDs) are the most common brominated flame-retardants after polybrominated diphenyl ethers. HBCDs can induce cancer by causing inappropriate antidiuretic hormone syndrome. Environmental contamination with HBCDs has been detected globally, with concentrations ranging from ng to mg. Methods to degrade HBCDs include physicochemical methods, bioremediation, and phytoremediation. The photodegradation of HBCDs using simulated sunlight or ultraviolet lamps, or chemical catalysts are inefficient and expensive, as is physicochemical degradation. Consequently, bioremediation is considered as the most cost-effective and clean approach. To date, five bacterial strains capable of degrading HBCDs have been isolated and identified: Pseudomonas sp. HB01, Bacillus sp. HBCD-sjtu, Achromobacter sp. HBCD-1, Achromobacter sp. HBCD-2, and Pseudomonas aeruginosa HS9. The molecular mechanisms of biodegradation of HBCDs are discussed in this review. New microbial resources should be explored to increase the resource library in order to identify more HBCD-degrading microbes and functional genes. Synthetic biology methods may be exploited to accelerate the biodegradation capability of existing bacteria, including modification of the degrading strains or functional enzymes, and artificial construction of the degradation microflora. The most potentially useful method is combining micro-degradation with physicochemical methods and phytoremediation. For example, exogenous microorganisms might be used to stimulate the adsorption capability of plants for HBCDs, or to utilize an interaction between exogenous microorganisms and rhizosphere microorganisms to form a new rhizosphere microbial community to enhance the biodegradation and absorption of HBCDs.

    Kun Wan, Wenfang Lin, Shuai Zhu, Shenghua Zhang, Xin Yu

    • Published data was used to analyze the fate of ARGs in water treatment.

    • Biomass removal leads to the reduction in absolute abundance of ARGs.

    • Mechanism that filter biofilm maintain ARB/ARGs was summarized.

    • Potential BAR risks caused by biofiltration and chlorination were proposed.

    The bacterial antibiotic resistome (BAR) is one of the most serious contemporary medical challenges. The BAR problem in drinking water is receiving growing attention. In this study, we focused on the distribution, changes, and health risks of the BAR throughout the drinking water treatment system. We extracted the antibiotic resistance gene (ARG) data from recent publications and analyzed ARG profiles based on diversity, absolute abundance, and relative abundance. The absolute abundance of ARG was found to decrease with water treatment processes and was positively correlated with the abundance of 16S rRNA (r2 = 0.963, p<0.001), indicating that the reduction of ARG concentration was accompanied by decreasing biomass. Among treatment processes, biofiltration and chlorination were discovered to play important roles in shaping the bacterial antibiotic resistome. Chlorination exhibited positive effects in controlling the diversity of ARG, while biofiltration, especially granular activated carbon filtration, increased the diversity of ARG. Both biofiltration and chlorination altered the structure of the resistome by affecting relative ARG abundance. In addition, we analyzed the mechanism behind the impact of biofiltration and chlorination on the bacterial antibiotic resistome. By intercepting influent ARG-carrying bacteria, biofilters can enrich various ARGs and maintain ARGs in biofilm. Chlorination further selects bacteria co-resistant to chlorine and antibiotics. Finally, we proposed the BAR health risks caused by biofiltration and chlorination in water treatment. To reduce potential BAR risk in drinking water, membrane filtration technology and water boiling are recommended at the point of use.

    Hongqi Wang, Ruhan Jiang, Dekang Kong, Zili Liu, Xiaoxiong Wu, Jie Xu, Yi Li

    • Explaintheadsorption, uptake and transmembrane transport of PAHs by bacteria.

    • Analyze functional regulation of membrane proteins inthe transmembrane transport.

    • Proteomics technology such as iTRAQ labeling was used to access expressed proteins.

    • Single cell analysis technology wereused to study the morphological structure.

    In recent years, increasing research has been conducted on transmembrane transport processes and the mechanisms behind the microbial breakdown of polycyclic aromatic hydrocarbons (PAHs), including the role of membrane proteins in transmembrane transport and the mode of transmission. This article explains the adsorption, uptake and transmembrane transport of PAHs by bacteria, the regulation of membrane protein function during the transmembrane transport. There are three different regulation mechanisms for uptake, depending on the state and size of the oil droplets relative to the size of the microbial cells, which are (i) direct adhesion, (ii) emulsification and pseudosolubilization, and (iii) interfacial uptake. Furthermore, two main transmembrane transport modes are introduced, which are (i) active transport and (ii) passive uptake and active efflux mechanism. Meanwhile, introduce the proteomics and single cell analysis technology used to address these areas of research, such as Isobaric tags for relative and absolute quantitation (iTRAQ) technology and Nano Secondary ion mass spectrometry (Nano-SIMS). Additionally, analyze the changes in morphology and structure and the characteristics of microbial cell membranes in the process of transmembrane transport. Finally, recognize the microscopic mechanism of PAHs biodegradation in terms of cell and membrane proteins are of great theoretical and practical significance for understanding the factors that influence the efficient degradation of PAHs contaminants in soil and for remediating the PAHs contamination in this area with biotechnology.

    Xueqi Fan, Jie Gao, Wenchao Li, Jun Huang, Gang Yu

    • Isotope dilution method was developed for the determination of 27 PPCPs in water.

    • The established method was successfully applied to different types of water samples.

    • The correction effect of corresponding 27 ILSs over 70 d was investigated.

    • Benefit of isotopic dilution method was illustrated for three examples.

    Pharmaceuticals and personal care products (PPCPs) are a unique group of emerging and non-persistent contaminants. In this study, 27 PPCPs in various water samples were extracted by solid phase extraction (SPE), and determined by isotope dilution method using liquid chromatography coupled to tandem triple quadruple mass spectrometer (LC-MS/MS). A total of 27 isotopically labeled standards (ILSs) were applied to correct the concentration of PPCPs in spiked ultrapure water, drinking water, river, effluent and influent sewage. The corrected recoveries were 73%–122% with the relative standard deviation (RSD)<16%, except for acetaminophen. The matrix effect for all kinds of water samples was<22% and the method quantitation limits (MQLs) were 0.45–8.6 ng/L. The developed method was successfully applied on environmental water samples. The SPE extracts of spiked ultrapure water, drinking water, river and wastewater effluent were stored for 70 days, and the ILSs-corrected recoveries of 27 PPCPs were obtained to evaluate the correction ability of ILSs in the presence of variety interferences. The recoveries of 27 PPCPs over 70 days were within the scope of 72%–140% with the recovery variation<37% in all cases. The isotope dilution method seems to be of benefit when the extract has to be stored for long time before the instrument analysis.

    Mohsen Jalali, Ziba Hurseresht

    • DTPA and NH4OAc, HNO3 and EDTA, and MgCl2 and NH4NO3 had similar behavior.

    • In NH4OAc, DTPA, and EDTA, the possibility of re-adsorption of trace elements is low.

    • CaCl2 may be more suitable than other extracts in calcareous soils.

    Understanding trace elements mobility in soils, extracting agents, and their relationships with soil components, are essential for predicting their movement in soil profile and availability to plants. A laboratory study was conducted to evaluate extractability of cadmium (Cd), cobalt (Co), copper (Cu), nickel (Ni), and zinc (Zn) from calcareous soils utilizing various extracting agents to be specific CaCl2, DTPA, EDTA, HNO3, MgCl2, NaNO3, NH4NO3, and NH4OAc. Cluster analysis indicated that DTPA and NH4OAc, HNO3 and EDTA, and MgCl2 and NH4NO3 extracting agents yielded comparative values, whereas NaNO3 and CaCl2 have shown different behavior than other extracting agents for all studied trace elements. The speciation of extracted trace elements in solutions indicated that in the CaCl2, NaNO3, NH4NO3, and MgCl2 extracting agents most extracted Cd, Co, Ni, Zn, and part of Cu were as free ions and may be re-adsorbed on soils, leading to lower extractability, whereas, in the case of HNO3 extracting agent, the likelihood of re-adsorption of trace elements may be little. The results of speciation of trace elements using NH4OAc, DTPA, and EDTA extracting agents showed that Me-(Acetate)3, Me-(Acetate)2(aq), Me(DTPA)3, Me(EDTA)2, and MeH(EDTA) complexes dominated in solutions indicating that the extracted trace elements may not be re-adsorbed on soils, leading to higher extractability. The results of this study are useful for short and long-term evaluations of trace elements mobility and further environmental impacts.

    Jian Wang, Qun Wang, Xueli Gao, Xinxia Tian, Yangyang Wei, Zhen Cao, Chungang Guo, Huifeng Zhang, Zhun Ma, Yushan Zhang

    • Mesoporous silica nanoparticle was modified with 4-triethoxysilylaniline.

    • AMSN-based TFN-RO membranes were prepared for seawater desalination.

    • Water transport capability of the AMSN was limited by polyamide.

    • Polyamide still plays a key role in permeability of the TFN RO membranes.

    Mesoporous silica nanoparticles (MSN), with higher water permeability than NaA zeolite, were used to fabricate thin-film nanocomposite (TFN) reverse osmosis (RO) membranes. However, only aminoalkyl-modified MSN and low-pressure (less than 2.1 MPa) RO membrane were investigated. In this study, aminophenyl-modified MSN (AMSN) were synthesized and used to fabricate high-pressure (5.52 MPa) RO membranes. With the increasing of AMSN dosage, the crosslinking degree of the aromatic polyamide decreased, while the hydrophilicity of the membranes increased. The membrane morphology was maintained to show a ridge-and-valley structure, with only a slight increase in membrane surface roughness. At the optimum conditions (AMSN dosage of 0.25 g/L), when compared with the pure polyamide RO membrane, the water flux of the TFN RO membrane (55.67 L/m2/h) was increased by about 21.6%, while NaCl rejection (98.97%) was slightly decreased by only 0.29%. However, the water flux of the membranes was much lower than expected. We considered that the enhancement of RO membrane permeability is attributed to the reduction of the effective thickness of the PA layer.

    Lei Zheng, Xingbao Gao, Wei Wang, Zifu Li, Lingling Zhang, Shikun Cheng

    • Washed MSWI fly ash was used as partial cement or sand substitute.

    • Sand replacing is beneficial for strength, while cement replacement reduces strength.

    • Cementing efficiency factor and mortar pore structure explain the strength results.

    • Health risk assessment was conducted for MSWI fly ash blended cement mortar.

    • CR and HI contributed by different exposures and heavy metals were analyzed.

    The strength of cement substituted mortar decreases with the increase in fly ash amount, whereas the strength increases when the fly ash is blended as sand substitute. A mortar with highest strength (compressive strength= 30.2 Mpa; flexural strength= 7.0 Mpa) was obtained when the sand replacement ratio was 0.75%. The k value (cementing efficiency) of fly ash varied between 0.36 and 0.15 for the fly ash fraction in binder between 5% and 25%. The k values of fly ash used for sand replacement were all significantly above that used for cement substitution. The macropores assigned to the gaps between particles decreased when the fly ash was used as sand replacement, providing an explanation for the strength enhancement. The waste-extraction procedure (toxicity-sulphuric acid and nitric acid method (HJ/T 299-2007)) was used to evaluate metal leaching, indicating the reuse possibility of fly ash blended mortar. For the mortar with the mass ratio of fly ash to binder of 0.5%, the carcinogenic risks (CR) and non-carcinogenic hazard quotient (HQ) in sensitive scenario for blended mortar utilization were 9.66 × 10-7 and 0.06, respectively; these results were both lower than the threshold values, showing an acceptable health risk. The CR (9.89 × 10-5) and HQ (3.89) of the non-sensitive scenario for fly ash treatment exceeded the acceptable threshold values, indicating health risks to onsite workers. The main contributor to the carcinogenic and non-carcinogenic risk is Cr and Cd, respectively. The CR and HQ from inhalation was the main route of heavy metal exposure.

    Zhihao Si, Xinshan Song, Xin Cao, Yuhui Wang, Yifei Wang, Yufeng Zhao, Xiaoyan Ge, Awet Arefe Tesfahunegn

    • CW-Fe allowed a high-performance of NO3-N removal at the COD/N ratio of 0.

    • Higher COD/N resulted in lower chem-denitrification and higher bio-denitrification.

    • The application of s-Fe0 contributed to TIN removal in wetland mesocosm.

    • s-Fe0 changed the main denitrifiers in wetland mesocosm.

    Sponge iron (s-Fe0) is a porous metal with the potential to be an electron donor for denitrification. This study aims to evaluate the feasibility of using s-Fe0 as the substrate of wetland mesocosms. Here, wetland mesocosms with the addition of s-Fe0 particles (CW-Fe) and a blank control group (CW-CK) were established. The NO3-N reduction property and water quality parameters (pH, DO, and ORP) were examined at three COD/N ratios (0, 5, and 10). Results showed that the NO3-N removal efficiencies were significantly increased by 6.6 to 58.9% in the presence of s-Fe0. NH4+-N was mainly produced by chemical denitrification, and approximately 50% of the NO3-N was reduced to NH4+-N, at the COD/ratio of 0. An increase of the influent COD/N ratio resulted in lower chemical denitrification and higher bio-denitrification. Although chemical denitrification mediated by s-Fe0 led to an accumulation of NH4+-N at COD/N ratios of 0 and 5, the TIN removal efficiencies increased by 4.5%‒12.4%. Moreover, the effluent pH, DO, and ORP values showed a significant negative correlation with total Fe and Fe (II) (P<0.01). High-throughput sequencing analysis indicated that Trichococcus (77.2%) was the most abundant microorganism in the CW-Fe mesocosm, while Thauera, Zoogloea, and Herbaspirillum were the primary denitrifying bacteria. The denitrifiers, Simplicispira, Dechloromonas, and Denitratisoma, were the dominant bacteria for CW-CK. This study provides a valuable method and an improved understanding of NO3-N reduction characteristics of s-Fe0 in a wetland mesocosm.

    Yong Xiao, Changye Xiao, Feng Zhao

    Shewanella oneidensis MR-1 was acclimated to grow with Cr(VI) of 190 mg/L.

    • Whole genomes from 7 populations at different acclimation stages were sequenced.

    • Gene mutations mainly related to efflux pumps and transporters.

    • An adaptation mechanism of MR-1 to high concentration of Cr(VI) was proposed.

    Acclimation is the main method to enhance the productivity of microorganisms in environmental biotechnology, but it remains uncertain how microorganisms acquire resistance to high concentrations of pollutants during long-term acclimation. Shewanella oneidensis MR-1 was acclimated for 120 days with increasing hexavalent chromium (Cr(VI)) concentrations from 10 to 190 mg/L. The bacterium was able to survive from the highly toxic Cr(VI) environment due to its enhanced capability to reduce Cr(VI) and the increased cell membrane surface. We sequenced 19 complete genomes from 7 populations of MR-1, including the ancestral strain, the evolved strains in Cr(VI) environment on days 40, 80 and 120 and their corresponding controls. A total of 27, 49 and 90 single nucleotide polymorphisms were found in the Cr(VI)-evolved populations on days 40, 80 and 120, respectively. Nonsynonymous substitutions were clustered according to gene functions, and the gene mutations related to integral components of the membrane, including efflux pumps and transporters, were the key determinants of chromate resistance. In addition, MR-1 strengthened the detoxification of Cr(VI) through gene variations involved in adenosine triphosphate binding, electron carrier activity, signal transduction and DNA repair. Our results provide an in-depth analysis of how Cr(VI) resistance of S. oneidensis MR-1 is improved by acclimation, as well as a genetic understanding of the impact of long-term exposure of microorganisms to pollution.

    Baoyuan Guo, Jiao Meng, Xinyu Wang, Chengnan Yin, Weiyu Hao, Baiwen Ma, Zhang Tao

    • Pesticide residuals on mulching film of Shandong, Tianjin and Hebei.

    • Detected 29 pesticides in soil and 30 in mulching film.

    • Pesticides on plastic films: 86.4‒22213.2 ng/g and in soil: 9.3‒535.3 ng/g.

    • Pesticides on plastic films 20 times higher than in soil.

    Plastic debris as new pollutants attracts much attention in the recent years. The plastic mulching films is one of the most important plastic debirs source in the environment. The aim of this work was to investigate the current status of pesticide residues on the plastic mulching films. Based on the QuEChERS method, multi-residue methods for detection of pesticide residues with gas chromatography tandem mass spectrum (GC-MS) and high performance liquid chromatography tandem mass spectrum (HPLC-MS) were developed for the analysis of the pesticides residues in plastic film and soil samples from Tianjin, Hebei and Shandong. The total concentrations of pesticide residues were in the range of 86.4‒22213.2 ng/g in plastic film debris, which was about 20 times higher than that in soil (9.3‒535.3 ng/g). Residual level of pesticides varied greatly in different samples. The historical usage and recent application of pesticides were the main sources for pesticide residues on plastic films and soil. In short, plastic mulching films could act as a sink for pesticides in farmland and the ubiquitous pesticide residues on plastic films should draw more attention.

    Nan Wu, Weiyu Zhang, Shiyu Xie, Ming Zeng, Haixue Liu, Jinghui Yang, Xinyuan Liu, Fan Yang

    • Manure application increased the abundances of ARGs and MGEs in agricultural soils.

    • Five classes of ARGs and two MGEs were prevalent in manured and unfertilized soils.

    • Genera Pseudomonas and Bacteroidetes might be the dominant hosts of intI1 and ermF.

    • The abundances of ARGs positively correlated with TC, TN, OM, Cu, Zn, Pb and MGEs.

    Land application of manure tends to result in the dissemination of antibiotic resistance in the environment. In this study, the influence of long-term manure application on the enrichment of antibiotic resistance genes (ARGs) and mobile genetic elements (MGEs) in agricultural soils was investigated. All the analyzed eight ARGs (tetA, tetW, tetX, sulI, sulII, ermF, aac(6’)-Ib-cr and blaTEM) and two MGEs (intI1 and Tn916/1545) were detected in both the manured and control soils, with relative abundances ranging from 10-6 to 10-2. Compared with the control soil, the relative abundances of ARGs and MGEs in manured soils were enriched 1.0–18.1 fold and 0.6–69.1 fold, respectively. High-throughput sequencing analysis suggested that at the phylum level, the bacteria carrying intI1 and ermF might be mainly affiliated with Proteobacteria and Bacteroides, respectively. The dominant genera carrying intI1 and ermF could be Pseudomonas and Bacteroides, independent of manure application. Correlation analysis revealed that ARGs had strong links with soil physicochemical properties (TC, TN, and OM), heavy metals (Cu, Zn and Pb) and MGEs, indicating that the profile and spread of ARGs might be driven by the combined impacts of multiple factors. In contrast, soil pH and C/N exhibited no significant relationships with ARGs. Our findings provide evidence that long-term manure application could enhance the prevalence and stimulate the propagation of antibiotic resistance in agricultural soils.