Enhanced remediation of chlorpyrifos-contaminated soil by immobilized strain Bacillus H27.

Chlorpyrifos is a pesticide widely used in agricultural production with a relatively long residual half-life in soil. Addressing the problem of residual chlorpyrifos is of universal concern. In this study, rice hull biochar was used as an immobilized carrier to prepare the immobilized strain H27 for the remediation of chlorpyrifos-contamination soil. Soil microorganisms after remediation were investigated by ecotoxicological methods. The immobilized strain H27 had the highest removal rate of chlorpyrifos when 10% bacterial solution was added to the liquid medium containing 0.075-0.109 mm diameter biochar cultured for 22 hr. This study on the removal of chlorpyrifos by immobilized strain H27 showed that the initial concentration of chlorpyrifos in solution was 25 mg/L, and the removal rate reached 97.4% after 7 days of culture. In the soil, the removal rate of the immobilized bacteria group increased throughout the experiment, which was significantly higher than that of the free bacteria and biochar treatment groups. The Biolog-ECO test, T-RFLP and RT-RCR were used to study the effects of the soil microbial community and nitrogen cycling functional genes during chlorpyrifos degradation. It was found that ICP group had the highest diversity index among the four treatment groups. The microflora of segment containing 114 bp was the dominant bacterial community, and the dominant microflora of the immobilized bacteria group was more evenly distributed. The influence of each treatment group on ammonia-oxidizing bacteria (AOB) was greater than on ammonia-oxidizing archaea (AOA). This study offers a sound scientific basis for the practical application of immobilized bacteria to reduce residual soil pesticides.

Rhizosphere bacteria G-H27 significantly promoted the degradation of chlorpyrifos and fosthiazate.

Microbial remediation of polluted environments is the most promising and significant research direction in the field of bioremediation. In this study, chlorpyrifos and fosthiazate were selected as representative organophosphorus pesticides, wheat was the tested plant, and fluorescently labeled degrading Bacillus cereus G-H27 were the film-forming bacteria. Exogenous strengthening technology was used to establish degrading bacterial biofilms on the root surface of wheat. The influence of root surface-degrading bacterial biofilms on the enrichment of chlorpyrifos and fosthiazate in wheat was comprehensively evaluated. First, the fluorescently-labeled degrading bacteria G-H27 was constructed, and its film-forming ability was investigated. Second, the growth- promoting characteristics and degradation ability of the bacteria G-H27 were investigated. Finally, the degradation effect of the root surface-degrading bacterial biofilm on chlorpyrifos and fosthiazate was determined. The above research provides an important material basis and method for the bioremediation of pesticide-contaminated soil.

Fluopicolide-Induced Oxidative Stress and DNA Damage in the Earthworm Eisenia foetida.

Fluopicolide is a new benzamide fungicide with a unique mechanism of action and is toxic to some non-target organisms. However, there is a lack of research on the chronic toxicity of fluopicolide to earthworms. In this study, in order to evaluate the chronic toxicity of fluopicolide to earthworms, the levels of reactive oxygen species (ROS) and malondialdehyde (MDA), the activities of superoxide dismutase (SOD), catalase (CAT), and glutathione S-transferase (GST), and DNA oxidative damage (8-hyoxy-2-deoxyguanosine content) in earthworms were measured at 7, 14, 21, and 28 days after exposure to different concentrations (0, 0.1, 0.5, 1, 2.5, 5, and 10 mg/kg) of fluopicolide. In most treatment groups, the ROS levels increased significantly 7 days after exposure and then decreased gradually with an increase in exposure time, a certain dose-effect relationship. The antioxidant enzymes' activities (SOD and CAT) in most treatment groups were activated, showing an increasing trend at first and then a decreasing trend; however, the CAT activity in the high-concentration treatment group was inhibited 21 days after exposure. The GST activity and MDA content showed an increasing trend at first and then a decreasing trend, which was dependent on the dose. As a biomarker of DNA damage, the 8-OHdG content was positively correlated with the concentration of fluopicolide. The results showed that a low dose of fluopicolide could cause oxidative stress and DNA damage in earthworms.

[Chemical Oxygen Demand(COD) Composition and Contribution in Typical Waters of Baiyangdian Lake].

Chemical oxygen demand (COD) is an important index used to assess organic oxygen consumption pollution. To explore COD composition in the natural water in Baiyangdian Lake, the main composition, source, and influencing factors of oxygen-consuming organic substances in the water body were revealed through physical continuous classification, three-dimensional fluorescence, and other methods. The results showed that the COD of the two waters was affected by dissolved organic substances (protein-like and humus-like organic matters) with size of less than 220 nm (59%-93%), and inorganic substances had little effect on COD. The source of organic matter in overlying water was primarily affected by endophytic vegetation decomposition, sediment release (the release flux of TOC was in the range of 1.55-2.28 mg·(m2·d)-1), and other endogenous sources (biological index>0.8), as well as by land-based sources such as reed platform and artificial pollution (1.4

Immobilization of Bacillus Thuringiensis and applicability in removal of sulfamethazine from soil.

Microbial degradation is considered an essential and promising treatment for sulfadimidine contamination of soil. To address the low colonization rates and inefficiencies of typical antibiotic-degrading bacteria, sulfamethazine (SM2)-degrading strain H38 is converted into immobilized bacteria in this study. Results show that the removal rate of SM2 by immobilized strain H38 reaches 98% at 36 h, whereas the removal rate of SM2 by free bacteria reaches 75.2% at 60 h. In addition, the immobilized bacteria H38 exhibits tolerance to a wide range of pH (5-9) and temperature (20 °C-40 °C). As the amount of inoculation increases and the initial concentration of SM2 decreases, the removal rate of SM2 by the immobilized strain H38 increases gradually. Laboratory soil remediation tests show that the immobilized strain H38 can remove 90.0% of SM2 from the soil on the 12th day, which exceeds the removal by free bacteria by 23.9% in the same period. Additionally, the results show that the immobilized strain H38 enhances the overall activity of microorganisms in SM2-contaminated soil. Compared with the SM2 only (control group containing no bacteria) and free bacterial treatment groups, the gene expression levels of ammonia-oxidizing archaea, ammonia-oxidizing bacteria, cbbLG, and cbbM increased significantly in the treatment group with immobilized strain H38. This study shows that immobilized strain H38 can reduce the effect of SM2 on soil ecology to a greater extent than free bacteria, while providing safe and effective remediation.

New insights into the effects of antibiotics and copper on microbial community diversity and carbon source utilization.

Residual antibiotics (ABs) and heavy metals (HMs) are continuously released from soil, reflecting their intensive use and contamination of water and soil, posing an environmental problem of great concern. Relatively few studies exist of the functional diversity of soil microorganisms under the combined action of ABs and HMs. To address this deficiency, BIOLOG ECO microplates and the Integrated Biological Responses version 2 (IBRv2) method were used to comprehensively explore the effects of single and combined actions of copper (Cu) and enrofloxacin (ENR), oxytetracycline (OTC), and sulfadimidine (SM2) on the soil microbial community. The results showed that the high concentration (0.80 mmol/kg) compound group had a significant effect on average well color development (AWCD) and OTC showed a dose-response relationship. The results of IBRv2 analysis showed that the single treatment group of ENR or SM2 had a significant effect on soil microbial communities, and the IBRv2 of E1 was 5.432. Microbes under ENR, SM2, and Cu stress had more types of available carbon sources, and all treatment groups were significantly more enriched with microorganisms having D-mannitol and L-asparagine as carbon sources. This study confirms that the combined effects of ABs and HMs can inhibit or promote the function of soil microbial communities. In addition, this paper will provide new insights into IBRv2 as an effective method to evaluate the impacts of contaminants on soil health.

Effect of sulfamethazine on the horizontal transfer of plasmid-mediated antibiotic resistance genes and its mechanism of action.

As a new type of environmental pollutant, antibiotic resistance genes (ARGs) pose a huge challenge to global health. Horizontal gene transfer (HGT) represents an important route for the spread of ARGs. The widespread use of sulfamethazine (SM2) as a broad-spectrum bacteriostatic agent leads to high residual levels in the environment, thereby increasing the spread of ARGs. Therefore, we chose to study the effect of SM2 on the HGT of ARGs mediated by plasmid RP4 from Escherichia coli (E. coli) HB101 to E. coli NK5449 as well as its mechanism of action. The results showed that compared with the control group, SM2 at concentrations of 10 mg/L and 200 mg/L promoted the HGT of ARGs, but transfer frequency decreased at concentrations of 100 mg/L and 500 mg/L. The transfer frequency at 200 mg/L was 3.04 × 10-5, which was 1.34-fold of the control group. The mechanism of SM2 improving conjugation transfer is via enhancement of the mRNA expression of conjugation genes (trbBP, trfAP) and oxidative stress genes, inhibition of the mRNA expression of vertical transfer genes, up regulation of the outer membrane protein genes (ompC, ompA), promotion of the formation of cell pores, and improvement of the permeability of cell membrane to promote the conjugation transfer of plasmid RP4. The results of this study provide theoretical support for studying the spread of ARGs in the environment.

Resistance selection of triflumezopyrim in Laodelphax striatellus (fallén): Resistance risk, cross-resistance and metabolic mechanism.

The risk assessment and resistance mechanisms of insecticide resistance are critical for resistance management strategy before a new insecticide is widely used. Triflumezopyrim (TFM) is the first commercialized mesoionic insecticide, which can inhibit nicotinic acetylcholine receptor with high-performance against the small brown planthopper (SBPH), Laodelphax striatellus (Fallén). In our study, the resistance of SBPH to TFM increased 26.29-fold, and the actual heritability of resistance was 0.09 after 21 generations of continuous selection by TFM. After five generations of constant feeding under insecticide-free conditions from F16 generation, the resistance level decreased 2.05-fold, and the average resistance decline rate per generation was 0.01, but there were no statistical decline. The TFM resistant strains had no cross-resistance to imidacloprid, nitenpyram, thiamethoxam, dinotefuran, flonicamid, pymetrozine, and chlorfenapyr. The third and fifth nymphal stage duration, pre-adult stage, adult preoviposition period, longevity, emergence rate, and hatchability of the resistant strain were significantly lower than those of the susceptible strain, while the female-male ratio was considerably increased. The fitness cost was 0.89. Further, cytochrome P450 monooxygenase (P450) and carboxylesterase (CarE) activities were markedly increased, but only the enzyme inhibitor piperonyl butoxide (PBO) had a significant synergistic effect on the resistant strain. The expression of CYP303A1, CYP4CE2, and CYP419A1v2 of P450 genes was significantly increased. SBPH has a certain risk of resistance to TFM with continuous application. The TFM resistance may be due to the increased activity of P450 enzyme regulated by the overexpression of P450 genes.

Mechanism for biodegradation of sulfamethazine by Bacillus cereus H38.

Degradation of sulfonamides (SAs) by microorganisms has become a focus of current research. Sulfamethazine (SMZ) is a type of SA widely used in the livestock and poultry industry. However, understanding the intermediate products, degradation pathways and mechanism of SMZ biodegradation is limited at present. In this study, a SMZ degrading bacterium Bacillus cereus H38, which can use SMZ as its only carbon source, was isolated from farmland soil. The bacterium was gram-positive with rod-shaped cells. The effects of initial SMZ concentration, pH, temperature and amount of inoculation on the biodegradation of SMZ were investigated by a single factor experiment. The results showed that the maximum degradation rate of SMZ was achieved in the environmental conditions at an initial SMZ concentration of 5 mg/L, pH of 7.0, temperature of 25 °C and inoculation amount of 5%. Under these optimum degradation conditions, strain H38 can completely degrade SMZ within 3 days. The effects of intracellular enzymes, extracellular enzymes and periplasmic enzymes on the SMZ degradation process were compared. It was found that intracellular enzymes contributed the most to the biodegradation of SMZ, and the degradation rate approached 70%. Three possible intermediates were identified by LC-MS/MS, and two degradation pathways were proposed. Whole genome sequencing results showed that the genome size of strain H38 was 5,477,631 bp, including 5599 coding sequences (CDSs), and the GC content was 35.21%. In addition, functional annotation of CDSs was performed to analyze the metabolic pathways of nitrogen and sulfur in strain H38 combining genomics and bioinformatics. This study proposes new insights into the mechanism for biodegradation of SAs and will inform future research.

Oxidative stress and DNA damage in earthworm (Eisenia fetida) induced by triflumezopyrim exposure.

Triflumezopyrim is an excellent pesticide for preventing and controlling rice planthoppers. It is widely used in the production of field rice and mainly through spraying with some inadvertent loss of pesticide to the soil. The future may bring development and utilization of seeds containing triflumezopyrim which will certainly impact earthworms. To evaluate the toxic effects of triflumezopyrim on earthworms, reactive oxygen species (ROS), superoxide dismutase (SOD) and catalase (CAT) activities, malondialdehyde content (MDA), glutathione S-transferase (GST), and DNA oxidative damage (8-hydroxy-2'-deoxyguanosine, 8-OHdG) were measured after 7, 14, 21, and 28 d analyzing the effects of 6 concentrations (0, 0.5, 1, 2.5, 5 and 10 mg/kg) of triflumezopyrim, respectively. ROS content did not change significantly in the early stages but showed a significant dose-effect relationship in the late stages. Antioxidant enzymes were activated in most treatment groups, and catalase activity was the same as that in the control group at 28 d. GST activity showed a trend of increasing first and then decreasing whereas MDA content had no obvious change in trend. 8-OHdG showed significant positive correlation with the concentration of triflumezopyrim at 28 d, indicating that the degree of DNA oxidative damage increased accordingly. The results showed that chronic exposure of triflumezopyrim may cause both oxidative stress and DNA damage in earthworms and alter the activity of antioxidant enzymes.

[Spatial distribution character of phosphorus fractions in surface sediment from Chaohu Lake].

Phosphorus fractions, organic matter and particle size of the surface sediment from Chaohu Lake were analyzed for spatial distribution and the risk of phosphorus release. The result showed that total phosphorus (TP) of surface sediment was 790 mg x kg(-1), which was 55% higher than that in 1980s, with 386 mg x kg(-1) higher in western lake and 211 mg x kg(-1) higher in eastern lake. NaOH-Pi of sediment ranged from 55 to 648 mg x kg(-1), and occupied average 25% of TP. NaOH-Po of sediment ranged from 27 to 468 mg x kg(-1), and occupied average 17% of TP. NaOH-Pi and NaOH-Po in western lake were 331 mg x kg(-1) and 225 mg x kg(-1), which were significantly higher than those in eastern lake. Ca-P and Res-P accounted for 18% and 40% of TP, and were equably distributed in the lake. TP, NaOH-Pi and NaOH-Po of sediment in the western lake increased intensively with the depth, while Ca-P and Res-P showed no significant change in the vertical profile in the lake. Profile of phosphorus fractions showed that NaOH-Pi and NaOH-Po were the dominant factions of the increasing phosphorus sedimentation in the western lake. Phosphorus of sediment in the western lake will release more easily to the water with higher organic matter and higher content of sandy silt.

Metals in sediment/pore water in Chaohu Lake: distribution, trends and flux.

Nine metals, Cd, Cu, Ni, Pb, As, Cr, Zn, Fe, and Mn in sediment and pore water from 57 sampling sites in Chaohu Lake (Anhui Province, China) were analyzed for spatial distribution, temporal trends and diffuse flux in 2010. Metals in the surface sediment were generally the highest in the western lake center and Nanfei-Dianbu River estuary, with another higher area of As, Fe, and Mn occurring in the Qiyang River estuary. Metal contamination assessment using the New York sediment screening criteria showed that the sediment was severely contaminated in 44% of the area with Mn, 20% with Zn, 16% with Fe, 14% with As, and 6% with Cr and Ni. An increasing trend of toxic metals (Cd, Cu, Ni, Pb, As, Cr, Zn) and Mn with depth was shown in the western lake. Compared with metal content data from the sediment survey conducted in 1980s, the metal content of surface sediment in 2010 was 2.0 times that in the 1980s for Cr, Cu, Zn, and As in the western lake, and less than 1.5 times higher for most of the metals in the eastern lake. Among the metals, only Mn and As had a widespread positive diffuse flux from the pore water to overlying water across the whole lake. The estimated flux in the whole lake was on average 3.36 mg/(m2 x day) for Mn and 0.08 mg/(m2 x day) for As, which indicated a daily increase of 0.93 microg/L for Mn and 0.02 microg/L for As in surface water. The increasing concentration of metals in the sediment and the flux of metals from pore water to overlying water by diffusion and other physical processes should not be ignored for drinking-water sources.

[Effect of iron plaque on root surfaces on phosphorus uptake of two wetland plants].

In situ micro-suction cups were used to collect samples of soil solution with Arundo donax Linn and Typha latifolia from defined segments at rhizosphere in field. The experiment was conducted to elucidate the contribution of iron plaque while wetland plants were used to remove phosphorus. The reddish iron plaque was observed and measured on the surfaces of roots of Arundo donax Linn and Typha latifolia in the field, 20,170.8 mg/kg (fresh weight) for Arundo donax Linn and 7640.3 mg/kg (fresh weight) for Typha latifolia were collected. Olsen-P contents of Arundo donax Linn with iron plaque were 28.85 mg/kg, 46.2% more than that of without, 34.99 mg/kg for Typha latifolia 21.9% more than that of without. The phosphate concentrations in the in situ rhizosphere soil solution of Arundo donax Linn with iron plaque were 0.65 mg/kg, 9.2% more than that of without, 0.56 mg/kg for Typha latifolia, 33.9% more than that of without. The phosphorus contents adsorbed by iron plaque were 81.7% for Arundo donax Linn and 85.7% for Typha latifolia of the wetland plants with iron plaque. Phosphate use efficiency of Arundo donax Linn with iron plaque was 16.5% more than that of without, 31.4% for Typha latifolia. The contents of phosphorus of single plant of the two wetland plants with iron plaque are higher than that of without. Due to adsorb phosphate with iron plaque, the transfer speeds of phosphate from non-rhizosphere to rhizosphere and from soil to soil solution are increasing. The phosphorus contents with iron plaque accumulated at rhizosphere and depleted at rhizosphere without iron plaque of Arundo donax Linn and Typha latifolia.

[In situ dynamics of phosphorus in the rhizosphere solution and organic acids exudation of two aquatic plants].

A mini-rhizotron experiment with Alternanthera philoxeroides and Typha latifolia was conducted to measure the spatial and temporal dynamics of phosphorus in the rhizosphere solution. The organic acids in the in situ rhizosphere soil solution were analyzed. A decreasing phosphorus concentration gradient in soil solution toward the root was observed for both A. philoxeroides and T. latifolia. The phosphorus concentration in the rhizosphere soil solution of A. philoxeroides (2.53 mg x L(-1)) was lower than that of T. latifolia (5.43 mg x L(-1)) in the forth sampling day. Compared to T. latifolia, A. philoxeroides released more malic acid (27.33 umol x L(-1)) which was more efficient in phosphorus mobilization. A. philoxeroides was more effective in phosphorus uptake in the rhizosphere than T. latifolia.

[Phosphorus rhizosphere depletion effect of four aquatic plants].

Four aquatic plants (Alternanthera philoxeroides, Typha latifolia, Sagittaria sagittifolia, Phragmites communis ) were cultured on P-enriched soil in a pot experiment to assess the phosphorus rhizosphere depletion effect and analysis the ratio of root to shoot, root morphology, phosphorus uptake efficiency and phosphorus use efficiency. An obvious variation in P concentration of the soil in the rhizophere and non- rhizophere was observed. Compared with the non-rhizosphere (available P: 167.53 microg x g(-1)), the available P in the rhizosphere soil of Alternanthera philoxeroides, Typha latifolia, Sagittaria sagittifolia and Phragmites communis was reduced to 80.17, 124.37, 155.38 and 161.75 microg x g(-1) respectively, with 81%, 42%, 18% and 16% reduction ratio of water-soluble phosphorus. More effective phosphorus depletion was achieved in Alternanthera philoxeroides by higher phosphorus uptake efficiency (1.32 mg x m(-1)), while rooting system was small and phosphorus use efficiency was low (0.34 g x mg(-1)). Phosphorus uptake efficiency of Typha latjfolia is much lower (0.52 mg x m(-1)) than that of Alternanthera philoxeroides, however, its strong rooting system enhanced soil exploration, with higher phosphorus use efficiency (0.64 g x mg(-1)) and the ratio of root to shoot (0.35). Alternantshera philoxeroides and Typha latfolia were more effective in phosphorus depletion of the rhizosphere soil than that in Sagittaria sagittifolia and Phragmites communis.