Influence of kaolinite and montmorillonite on benzo[a]pyrene biodegradation by Paracoccus aminovorans HPD-2 and the underlying interface interaction mechanisms

Clay minerals play an important role in biogeochemical cycling.Here,kaolinite and montmorillonite,the two most abundant and widespread clay minerals with typical layered structures,were selected to investigate and compare their effects on the biodegradation of benzo[a]pyrene(BaP)by Paracoccus aminovorans HPD-2 and to investigate the underlying interface mechanisms.Overall,the BaP degradation efficiency was significantly higher 7 d after montmorillonite addition,reaching 68.9%(P<0.05),when compared with that of the control without addition of clay minerals(CK,61.4%);however,the addition of kaolinite significantly reduced the BaP degradation efficiency to 45.8%.This suggests that kaolinite inhibits BaP degradation by inhibiting the growth of strain HPD-2,or its strong hydrophobicity and readily agglomerates in the degradation system,resulting in a decrease in the bio-accessibility of BaP to strain HPD-2.Montmorillonite may buffer some unfavorable factors,and cells may be fixed on the surface of montmorillonite colloidal particles across energy barriers.Furthermore,the adsorption of BaP on montmorillonite may be weakened after swelling,reducing the effect on the bio-accessibility of BaP,thus promoting the biodegradation of BaP by strain HPD-2.The experimental results indicate that differential bacterial growth,BaP bio-accessibility,interface interaction,and the buffering effect may explain the differential effects of the different minerals on polycyclic aromatic hydrocarbon biodegradation.These observations improve our understanding of the mechanisms by which clay minerals,organic pollutants,and degrading bacteria interact during the biodegradation process and provide a theoretical basis for increasing the biodegradation of soil pollutants by native microorganisms under field conditions.

The frontier of soil science: Soil health

Soils are a valuable resource with life activity in terrestrial ecosystem,and soil health and its sustainable management are becoming a major focus of global concern.A healthy soil is a“harmonious social system”,which should have good structure,functional state,and buffering performance to maintain the dynamic balance of soil ecosystem.Soil health has become the frontier of soil science.The development of theoretical and practical approaches for soil health evaluation and management is urgently needed.Therefore,further research is needed to develop new techniques and methods for soil health research,construct soil health index and evaluation system,clarify the mechanism and spatial-temporal pattern of soil health conservation,and establish soil health protection and cultivation technology,which would provide scientific and technological support for soil resource protection and sustainable utilization.

A review of the gas hydrate phase transition with a microfluidic approach

Over the years,natural gas hydrates(NGHs)have attracted significant attention as an emerging energy resource.Microfluidics is a novel technology used to observe the behaviour of NGHs in microchannels directly and has been applied to hydrates.Gas hydrate distributions and phase transitions are key parameters for exploitation and application.In this paper,advances in related research with microfluidics-based technology are reviewed,including the hydrate phase transition process and its mechanism of influence.Hydrate formation and decomposition directly influence the efficiency and sustainability of exploitation.In addition,studies of the hydrate phase transition provide basic data for future commercial exploitation.Moreover,extended applications,further developments and potential improvements in microfluidic techniques are also discussed.We believe that with an improved understanding of the hydrate phase transition mechanism,commercial exploitation of hydrates can be expected soon.

Effects of long-term fertilizer applications on peanut yield and quality and plant and soil heavy metal accumulation

The status of essential and potentially toxic trace elements in soils and crops can be affected by long-term fertilization practices. This study aimed to investigate changes in peanut (Arachis hypogaea L.) yield and kernel quality, and changes in copper (Cu), zinc (Zn), lead (Pb), and cadmium (Cd)concentrations in soil and peanut kernels after 16 years of continuous cropping with different fertilization treatments. Five fertilization treatments were applied at a red soil site in Southeast China:chemical fertilizer (F) containing nitrogen, phosphorus, and potassium, F+trace elements (FT), pig manure (M), M+effective microorganisms (MB), and MB+trace elements (MBT). Properties of soil and pig manure, heavy metal contents in soil and peanut kernels, and the compositions of amino and fatty acids in kernels were determined. Application of pig manure significantly increased peanut biomass, kernel yield, and crude protein and total amino acid contents in kernels, but led to higher amounts of Cu, Zn, and Cd in soil and higher amounts of Zn and Cd in peanut kernels compared with that of chemical fertilizer. There should be greater concern about potential kernel Cd and Zn contaminations resulting from long-term application of pig manure contaminated with potentially toxic metals as an organic fertilizer.

Adsorption and desorption characteristics of diphenylarsenicals in two contrasting soils

Diphenylarsinic acid （DPAA） is formed during the leakage of aromatic arsenic chemical weapons in soils, is persistent in nature, and results in arsenic contamination in the field. The adsorption and desorption characteristics of DPAA were investigated in two typical Chinese soils, an Acrisol （a variable-charge soil） and a Phaeozem （a constant-charge soil）. Their thermodynamics and some of the factors influencing them （i.e., initial pH value, ionic strength and phosphate） were also evaluated using the batch method in order to understand the environmental fate of DPAA in soils. The results indicate that Acrisol had a stronger adsorption capacity for DPAA than Phaeozem. Soil DPAA adsorption was a spontaneous and endothermic process and the amount of DPAA adsorbed was affected significantly by variation in soil pH and phosphate. In contrast, soil organic matter and ionic strength had no significant effect on adsorption. This suggests that DPAA adsorption may be due to specific adsorption on soil mineral surfaces. Therefore, monitoring the fate of DPAA in soils is recommended in areas contaminated by leakage from chemical weapons.

Phytotoxicity in seven higher plant species exposed to di-n-butyl phthalate or bis （2-ethylhexyl） phthalate

We investigated phytotoxicity in seven plant species exposed to a range of concentrations （0- 500 mg· kg^-1 soil） of di-n-butyl phthalate （DnBP） or his （2- ethylhexyl） phthalate （DEHP）, two representative phthalate esters （PAEs） nominated by USEPA as priority pollutants and known environmental estrogens. We studied seed germination, root elongation, seedling growth, biomass （fresh weight, FW） and malondialdehyde （MDA） content of shoots and roots of wheat （Triticum aestivum L.）, alfalfa （Medicago sativa L.）, perennial ryegrass （Lolium perenne）, radish （Raphanus sativus L.）, cucumber （Cucumis sativus L.）, oat （Avena sativa） and onion （Allium cepa L.）, together with monitoring of plant pigment content （chlorophyll a, b and earotinoids） in alfalfa, radish and onion shoots. Root elongation, seedling growth and biomass of the test species were generally inhibited by DnBP but not by DEHP, indicating a lower level of phytotoxicity of DEHP than of DnBP. MDA contents of four species were promoted by PAE exposure, but not in alfalfa, ryegrass or onion shoots, indicating lower sensitivity of these three species to PAE pollutants. Plant pigment contents were clearly affected under the stress of both pollutants, implying the potential damage to the photosynthetic system of test plants, mainly by decreasing the content of chlorophyll a and b. Results of DnBP and DEHP phytotoxicity to the primary growth of test plants has provided information for the assessment of their environmental risk in the soil and also forms a basis for the further analysis of their toxic effects over the whole growth period of different plant species.

Dissipation of polycyclic aromatic hydrocarbons and microbial activity in a field soil planted with perennial ryegrass

Dissipation and plant uptake of polycyclic aromatic hydrocarbons （PAHs） in contaminated agricul- tural soil planted with perennial ryegrass were investigated in a field experiment. After two seasons of grass cultivation the mean concentration of 12 PAHs in soil decreased by 23.4% compared with the initial soil. The 3-, 4-, 5-, and 6- ring PAHs were dissipated by 30.9%, 25.5%, 21.2%, and 16.3% from the soil, respectively. Ryegrass shoots accumulated about 280 ug.kg1, shoot dry matter biomass reached 2.48 x 104kg-ha1, and plant uptake accounted for about 0.99% of the decrease in PAHs in the soil. Significantly higher soil enzyme activities and microbial community functional diversity were observed in planted soil than that in the unplanted control. The results suggest that planting ryegrass may promote the dissipation of PAHs in long-term contaminated agricultural soil, and plant-promoted microbial degradation may be a main mechanism of phytoremediation.

Microbial remediation of a pentachloronitrobenzene-contaminated soil under Panax notoginseng: A field experiment

Pentachloronitrobenzene(PCNB)is an organochlorine fungicide that is mainly used in the prevention and control of diseases in crop seedlings.Microbial removal is used as a promising method for in-situ removal of many organic pesticides and pesticide residues.A short-term field experiment(1 year)was conducted to explore the potential role of a PCNB-degrading bacterial isolate,Cupriavidus sp.YNS-85,in the remediation of a PCNB-contaminated soil on which Panax notoginseng was grown.The following three treatments were used:i)control soil amended with wheat bran but without YNS-85,ii)soil with 0.15 kg m-2of solid bacterial inoculum(A),and iii)soil with 0.30 kg m-2of solid bacterial inoculum(B).The removal of soil PCNB during the microbial remediation was monitored using gas chromatography.Soil catalase and fluorescein diacetate(FDA)esterase activities were determined using spectrophotometry.In addition,cultivable bacteria,fungi,and actinomycetes were counted by plating serial dilutions,and the microbial biodiversity of the soil was analyzed using BIOLOG.After 1 year of in-situ remediation,the soil PCNB concentrations decreased significantly by 50.3%and 74.2%in treatments A and B,respectively,when compared with the uninoculated control.The soil catalase activity decreased in the presence of the bacterial isolate,the FDA esterase activity decreased in treatment A,but increased in treatment B.No significant changes in plant biomass,diversity of the soil microbial community,or physicochemical properties of the soil were observed between the control and inoculated groups(P<0.05).The results indicate that Cupriavidus sp.YNS-85 is a potential candidate for the remediation of PCNB-contaminated soils under P.notoginseng.

A highly effective polycyclic aromatic hydrocarbon-degrading bacterium,Paracoccus sp.HPD-2,shows opposite remediation potential in two soil types

Bioaugmentation is an efficient and eco-friendly strategy for the bioremediation of polycyclic aromatic hydrocarbons(PAHs).Since the degrading abilities of soils can greatly alter the abilities of PAH-degrading bacteria,illustrating the potential and mechanism of highly efficient degrading bacteria in different soil environments is of great importance for bioremediation.A PAH-degrading bacterium,Paracoccus aminovorans HPD-2,and two soil types,red and paddy soils,with distinct PAH-degrading abilities,were selected for this study.A soil microcosm experiment was performed by adding pyrene(PYR)and benzo[a]pyrene(B[a]P).Illumina sequencing was used to examine bacterial community structure.The results showed that inoculation with HPD-2 significantly elevated PYR and B[a]P degradation rates by 44.7%and 30.7%,respectively,in the red soil,while it only improved the degradation rates by 1.9%and 11%,respectively,in the paddy soil.To investigate the underlying mechanism,the fate of strain HPD-2 and the response of the indigenous bacterial communities were determined.Strain HPD-2 occupied certain niches in both soils,and the addition of the bacterium changed the native community structure more noticeably in the red soil than in the paddy soil.The addition of PAHs and strain HPD-2 significantly changed the abundances of 7 phyla among the 15 detected phyla in the red soil.In the paddy soil,5 of the 12 dominant phyla were significantly affected by PAHs and the inoculation of HPD-2,while 6new phyla were detected in the low-abundance phyla(<0.1%).The abundances of Massilia,Burkholderia,and Rhodococcus genera with PAH degradation efficiency were significantly increased by the inoculation of HPD-2 in the red soil during 42 d of incubation.Meanwhile,in the paddy soil,the most dominant effective genus,Massilia,was reduced by HPD-2 inoculation.This research revealed the remediation ability and inherent mechanism of the highly effective PAH-degrading strain HPD-2 in two different soil types,which would provide a theoretical basis for the application of degrading bacteria in different soils.

Proteomic response of wheat embryos to fosthiazate stress in a protected vegetable soil

A proteomic analysis of wheat defense response induced by the widely used organophosphorus nematicide fosthiazate is reported. Seed germination and two-dimensional gel electrophoresis （2-DE） experiments were performed using a Chinese wheat cultivar, Zhenmai No. 5. Root and shoot elongation decreased but thiobarbituric acid reactive substances （TBARS） content in embryos increased with increasing pesticide concentration. More than 1000 protein spots were reprodueibly detected in each silver-stained gel. Thirty-seven protein spots with at least 2-fold changes were identified using MALDI-TOF MS/MS analysis. Of these, 24 spots were up-regulated and 13 were down-regulated. Proteins identified included some well-known classical stress responsive proteins under abiotic or biotic stresses as well as some unusual responsive proteins. Ten responsive proteins were reported for the first time at the proteomic level, including fatty acyl CoA reductase, dihydrodipicolinate synthase, DEAD-box ATPase-RNA-helicase, fimbriata-like protein, waxy B 1, rust resistance kinase Lrl0, putative In2.1 protein, retinoblastoma-related protein 1, pollen allergen-like protein and S-adenosyl-L- methionine：phosphoethanolamine N-methyltransferase. The proteins identified were involved in several processes such as metabolism, defense/detoxification, cell structure/ceU growth, signal transduction]transcription, photosynthesis and energy. Seven candidate proteins were further analyzed at the mRNA level by RT-PCR to compare transcript and protein accumulation patterns, revealing that not all the genes were correlated well with the protein level. Identification of these responsive proteins may provide new insight into the molecular basis of the fosthiazate-stress response in the early developmental stages of plants and may be useful in stress monitoring or stress-tolerant crop breeding for environmentally friendly agricultural production.

Reductive dechlorination of polychlorinated biphenyls is coupled to nitrogen fixation by a legume-rhizobium symbiosis

Chlorinated persistent organic pollutants, including polychlorinated biphenyls （PCBs）, represent a particularly serious environmental problem and human health risk worldwide. Leguminous plants and their symbiotic bacteria （rhizobia） are important components of the biogeochemical cycling of nitrogen in both agricultural and natural ecosystems. However, there have been relatively few detailed studies of the remediation of PCB-contaminated soils by legume-rhizobia symbionts. Here we report for the first time evidence of the reductive dechlorination of 2,4,4＇-trichlorobiphenyl （PCB 28） by an alfalfa-rhizobium nitrogen fixing symbiont. Alfalfa （Medicago sativa L.） inoculated with wild-type Sinorhizobiurn meliloti had significantly larger biomass and PCB 28 accumulation than alfalfa inoculated with the nitrogenase negative mutant rhizobium SmY. Dechlorination products of PCB 28, 2,4＇-dichlorobiphenyl （PCB 8）, and the emission of chloride ion （C1-） were also found to decrease significantly in the ineffective nodules infected by the mutant strain SmY. We therefore hypothesize that N2-fixation by the legume-rhizobium symbiont is coupled with the reductive dechlorination of PCBs within the nodules. The combination of these two processes is of great importance to the biogeochemical cycling and bioremediation of organochlorine pollutants in terrestrial ecosystems.

Legacy of herbicides in water from Hailun City,Northeast China:Occurrence,source,and ecological risk assessment

Herbicides(HBCs)are extensively used in modern agriculture.However,their potential negative impacts on environmental media have emerged as a significant environmental concern.In this study,we employed positivematrix factorization(PMF)to identify the potential sources of HBCs.Furthermore,we utilized amulti-matrix ecological riskmodel to assess the risks associated with HBCs in both surface water and groundwater in the black soil region of Northeast China.The findings revealed that the levels of15HBCs in surface water and groundwater ranged from585.84 to 6466.96 ng/L and 4.80 to 11,774.64 ng/L,respectively.The PMF results indicated that surface runoff and erosion accounted for 50%of the total HBCs in water,serving as the primary sources.All tested HBCs exhibited acute risk values within acceptable levels.The risk index for the∑15HBCs was categorized as“moderate risk”in 31%of the surface waters and 13%of the groundwaters.However,4%of the groundwater sampling sites reached the“high risk”level.The chronic risk quotient of∑15HBCs in surface water and groundwater was 92%and 62%at the“high risk”level,respectively.Interestingly,noncarcinogenic HBCs contributed more significantly to the ecotoxicology of the aquatic system than carcinogenic HBCs.This study provides comprehensive information on the legacy of HBCs in water bodies and emphasizes the potential risks posed by HBCs to aquatic systems.The results obtained from this study could help relevant management authorities in developing and implementing effective regulations tomitigate the ecological and environmental risks associated with HBCs.