Rhizosphere Bacteria Help to Compensate for Pesticide-Induced Stress in Plants.

Although exogenous chemicals frequently exhibit a biphasic response in regulating plant growth, characterized by low-dose stimulation and high-dose inhibition, the underlying mechanisms remain elusive. This study demonstrates, for the first time, the compensatory function of rhizosphere microbiota in assisting plants to withstand pesticide stress. It was observed that pak choi plants, in response to foliar-spraying imidacloprid at both low and high doses, could increase the total number of rhizosphere bacteria and enrich numerous beneficial bacteria. These bacteria have capabilities for promoting plant growth and degrading the pesticide, such as Nocardioides, Brevundimonas, and Sphingomonas. The beneficial bacterial communities were recruited by stressed plants through increasing the release of primary metabolites in root exudates, such as amino acids, fatty acids, and lysophosphatidylcholines. At low doses of pesticide application, the microbial compensatory effect overcame pesticide stress, leading to plant growth promotion. However, with high doses of pesticide application, the microbial compensatory effect was insufficient to counteract pesticide stress, resulting in plant growth inhibition. These findings pave the way for designing improved pesticide application strategies and contribute to a better understanding of how rhizosphere microbiota can be used as an eco-friendly approach to mitigate chemical-induced stress in crops.

Foliar Spraying of Chlorpyrifos Triggers Plant Production of Linolenic Acid Recruiting Rhizosphere Bacterial Sphingomonas sp.

Plants have developed an adaptive strategy for coping with biotic or abiotic stress by recruiting specific microorganisms from the soil pool. Recent studies have shown that the foliar spraying of pesticides causes oxidative stress in plants and leads to changes in the rhizosphere microbiota, but the mechanisms by which these microbiota change and rebuild remain unclear. Herein, we provide for the first-time concrete evidence that rice plants respond to the stress of application of the insecticide chlorpyrifos (CP) by enhancing the release of amino acids, lipids, and nucleotides in root exudates, leading to a shift in rhizosphere bacterial community composition and a strong enrichment of the genus Sphingomonas sp. In order to investigate the underlying mechanisms, we isolated a Sphingomonas representative isolate and demonstrated that it is both attracted by and able to consume linolenic acid, one of the root exudates overproduced after pesticide application. We further show that this strain selectively colonizes roots of treated plants and alleviates pesticide stress by degrading CP and releasing plant-beneficial metabolites. These results indicate a feedback loop between plants and their associated microbiota allowing to respond to pesticide-induced stress.

Rice recruits Sphingomonas strain HJY-rfp via root exudate regulation to increase chlorpyrifos tolerance and boost residual catabolism.

Inoculation with pollution-degrading endophytes boosts the catabolism of residual contaminants and promotes the pollution adaptation of host plants. We investigated the interaction pattern between Sphingomonas strain HJY-rfp, a chlorpyrifos-degrading endophytic bacterium, and rice (Oryza sativa) under pesticide stress using hydroponic cultivation. We observed a notable trend of endophytic root colonization in rice plants treated with 10 mg l-1 chlorpyrifos solution, and after 24 h the migration of HJY-rfp enhanced the chlorpyrifos degradation rate in leaves and stems by 53.36% and 40.81%, respectively. Critically, the rice root exudate profile (organic acids and amino acids) changed under chlorpyrifos stress, and variations in the contents of several components affected the chemotactic behaviour of HJY-rfp. HJY-rfp colonization dramatically activated defensive enzymes, which enabled efficient scavenging of reactive oxygen species, and led to 9.8%, 22.5%, and 41.9% increases in shoot length, fresh weight, and accumulation of total chlorophyll, respectively, in rice suffering from oxidative damage by chlorpyrifos. Endophytic colonization caused up-regulation of detoxification genes that have shown a significant positive correlation with chlorpyrifos degradation in vivo. Collectively, our results demonstrate that agrochemical stress causes plants to actively recruit specific symbiotic microbes to detoxify contaminants and survive better under pollution conditions.

Use of Bacillus-siamensis-inoculated biochar to decrease uptake of dibutyl phthalate in leafy vegetables.

Dibutyl phthalate (DBP) is a frequently detected farmland contaminant that is harmful to the environment and human health. In this study, a DBP-degrading endophytic Bacillus siamensis strain T7 was immobilized in rice husk-derived biochar for bioremediation of DBP-polluted agricultural soils. The effects of this microbe-biochar composite on the soil prokaryotic community and the mechanism by which it regulates DBP degradation, were also investigated. A supplement of T7-biochar composite not only significantly boosted DBP biodegradation in soil by raising the DBP degradation rate constant and half-life from 0.1979 d-1 and 2.3131 d to 0.2434 d-1 and 2.1062 d, respectively, but also impeded DBP uptake by leafy vegetables. The general bioremediation effect of T7-biochar alliance excelled pure T7 suspensions and biochar, by trapping more DBP and boosting its complete degradation in soil. Besides, the combination of strain T7 and biochar can increase the proportion of some beneficial bacteria and boost the functional diversity of soil prokaryotic community, then to a certain extent may reverse the negative effect of DBP pollution on the agricultural soils. These results indicate that the rice-husk-derived biochar is a proper media when utilizing functional microbes into environmental treatment. Overall, T7-biochar composite is a promising soil modifier for soil bioremediation and the production of DBP-free crops.

Major factors dominating the fate of dibutyl phthalate in agricultural soils.

Dibutyl phthalate (DBP) is a ubiquitous soil contaminant. We have investigated the sorption, degradation and residue of DBP in 20 types of agricultural soils and aimed to identify the major soil properties that dominate the fate of DBP. Sorption isotherms of DBP in all soils were fitted well with the Freundlich model. The sorption coefficient (Kf) varied between 3.99 and 36.1 mg1-1/nL1/n/kg. Path analysis indicated that 59.9% of variation in Kf could be explained by the combination of pH, organic carbon (OC) and clay content. Degradation of DBP in the 20 soils was well described by the first-order kinetic model, with half-lives (t1/2) ranging from 0.430 to 4.99 d. The residual DBP concentration after 60 d of incubation (R60) ranged from 0.756 to 2.15 mg/kg and the residual rates ranged from 3.97% to 9.63%. The Kf value was significantly positively correlated with t1/2 and R60. Moreover, soil pH, microbial biomass carbon (Cmic) and OC were identified as dominating factors that explained 84.4% of variation in t1/2. The R60 data indicated 72.2% of its variability attributable to the combination of OC and Cmic. The orders of the relative importance of dominating factors on the Kf, t1/2 and R60 were OC > pH > clay, Cmic > pH > OC and OC > Cmic, respectively. This work contributes to better understand the fate of DBP in soils and make scientific decisions about accelerating its dissipation in different soils.

Di-n-butyl phthalate degrading endophytic bacterium Bacillus amyloliquefaciens subsp. strain JR20 isolated from garlic chive and its colonization in a leafy vegetable.

Di-n-butyl phthalate (DBP) is one of the primary PAEs (phthalate acid esters) pollutants. DBP can be absorbed by plants and threaten human health via the food chain. Some DBP-degrading bacteria have been successfully isolated from the environment (water, soil, etc.). However, only a few DBP-degrading plant endophytes have been isolated. In this study, an endophytic bacterium, Bacillus amyloliquefaciens subsp. strain JR20, which was found capable of degrading DBP, was isolated from garlic chive. We found that strain JR20 metabolized 89.74% of DBP at a 5 mg/L concentration within 4 d in liquid mineral salts medium (MSM). The optimized conditions for maximum removal of DBP were as follows: DBP concentration, 5 mg/L; pH, 7-8; temperature, 30-40 °C. The colonization of strain JR20 significantly improved the degradation rate of DBP in the roots, stems and leaves of leafy vegetables.

Degradation of chlorpyrifos by an endophytic bacterium of the Sphingomonas genus (strain HJY) isolated from Chinese chives (Allium tuberosum).

The degradation of chlorpyrifos (CP) by an endophytic bacterial strain (HJY) isolated from Chinese chives (Allium tuberosum Rottl. ex Spreng) was investigated. Strain HJY was identified as Sphingomonas sp. based on morphological, physiological, and biochemical tests and a 16S rDNA sequence analysis. Approximately 96% of 20 mg L-1 CP was degraded by strain HJY over 15 days in liquid minimal salts medium (MSM). The CP degradation rate could also be increased by glucose supplementation. The optimal conditions for the removal of 20 mg L-1 CP by strain HJY in MSM were 2% inoculum density, pH 6.0, and 30-35°C. The CP degradation rate constant and half-life were 0.2136 ± 0.0063 d-1 and 3.2451 ± 0.0975 d, respectively, under these conditions, but were raised to 0.7961 ± 0.1925 d-1 and 0.8707 ± 0.3079 d with 1% glucose supplementation. The detection of metabolic products and screening for degrading genes indicated that O,O-diethyl O-3,5,6-trichloropyridinol was the major degradation product from CP, while it was likely that some functional genes were undetected and the mechanism responsible for CP degradation by strain HJY remained unknown. Strain HJY is potentially useful for the reduction of CP residues in Chinese chives and may be used for the in situ phytoremediation of CP.

Colonization Mechanism of Endophytic Enterobacter cloacae TMX-6 on Rice Seedlings Mediated by Organic Acids Exudated from Roots.

Small molecular organic acids (SMOAs) in root exudates are critical for plant-microbe interaction, especially under environmental stresses. However, the dominant organic acids driving the process and promoting the colonization are unclear. Here, using a target metabolomics, 20 main SMOAs of rice root exudates were identified and analyzed in control and 10 mg/L thiamethoxam-treated groups. The composition of these SMOAs differed significantly between the two treatments. Among which, malic acid, citric acid, succinic acid, and proline induced a chemotactic response, swimming ability, and biofilm formation of Enterobacter cloacae TMX-6 in a dose-dependent manner. The maximal chemotactic response of TMX-6 was induced by proline at 10 mg/L, and a strong chemotactic response was even observed at 0.01 mg/L. The recruitment assay confirmed that the addition of these four compounds promoted the colonization of TMX-6. The results provide insight for directional regulation of plant-microbe interactions for beneficial outcomes.

Stenotrophomonas pavanii DJL-M3 inoculated biochar stabilizes the rhizosphere soil homeostasis of carbendazim-stressed rice.

Plant-microbe interactions have been effectively used in phytoremediation to reduce agrochemical contamination of crops and soils, but little information is available regarding the general effect of such association on rhizosphere soil homeostasis. In this study, we immobilized Stenotrophomonas pavanii DJL-M3, a carbendazim (CBZ)-degrading endophyte, in rice husk-derived biochar to control fungicide residue in the rice microenvironment. The influence of biochar inoculated with strain DJL-M3 on rhizobacterial communities was also investigated, including activity and fundamental function predictions. An adsorption kinetics test showed that strain DJL-M3 slowed the adsorption rate slightly without sacrificing the adsorption capacity of rice-husk biochar on CBZ. Immobilization in biochar helped S. pavanii DJL-M3 to establish an ecological niche in rhizosphere soils. This process significantly reduced CBZ levels in rice and rhizosphere soil while maintaining stable heterotrophic microbial respiration and carbon (C) metabolic activity. Soil amendment with the strain DJL-M3-biochar composite resulted in relatively little disturbance of fundamental soil functions, such as nitrogen (N) and sulfur (S) cycling, which explained the better plant growth and higher soil fertility observed with CBZ contamination. Overall, the combination of biochar and S. pavanii DJL-M3 demonstrated the potential to safeguard the microbiological environment of rice.

Functional characterization of rice (Oryza sativa) thioredoxins for detoxification and degradation of atrazine.

Thioredoxins (TRXs) are a group of antioxidant enzymes that play a critical role in plant growth and resistance to stress. However, the functional role and mechanism of rice TRXs in response to pesticides (e.g. atrazine, ATZ) stress remain largely unexplored. Here, 24 differentially expressed TRX genes (14 up and 10 down) of ATZ-exposed rice were identified through high-throughput RNA-sequencing analysis. Twenty-four TRX genes were unevenly mapped to 11 chromosomes and some of the genes were validated by quantitative RT-PCR. Bioinformatics analysis revealed that ATZ-responsive TRX genes contain multiple functional cis-elements and conserved domains. To demonstrate the functional role of the genes in ATZ degradation, one representative TRX gene LOC_Os07g08840 was transformed into yeast cells and observed significantly lower ATZ content compared to the control. Using LC-Q-TOF-MS/MS, five metabolites were characterized. One hydroxylation (HA) and two N-dealkylation products (DIA and DEA) were significantly increased in the medium with positive transformants. Our work indicated that TRX-coding genes here were responsible for ATZ degradation, suggesting that thioredoxins could be one of the vital strategies for pesticide degradation and detoxification in crops.

[Determination and Traceability Analysis of Phthalic Acid Esters in Garlic (Allium stivum L.) from Jiangsu Province, China].

Phthalic acid esters (PAEs) are ubiquitous environmental pollutants and are recognized as a threat to the environment and agricultural product safety across the world. In order to investigate the level of PAEs in garlic, soils, and agricultural films from Pizhou City, Jiangsu province, China, 11 garlic samples, 106 soil samples, and 4 agricultural film samples were collected and analyzed using GC-MS. In addition, the uptake and transport characteristics of six PAEs compounds classified as priority pollutants by the United States Environmental Protection Agency (EPA) in the garlic cultivar Daqingke were investigated under hydroponic conditions. The results indicated that dibutyl phthalate (DBP) and di-(2-ethylhexyl) phthalate (DEHP) were the dominant PAEs species in garlic cloves of the different garlic varieties from Pizhou City. The average contents of DBP and DEHP in garlic cloves were 0.611 mg·kg-1 and 0.167 mg·kg-1, respectively, which were significantly higher than those of the commercial varieties of garlic. The concentrations of DBP and DEHP differed in three tissues of garlic bulbs, ordered as the skin of garlic bulb>skin of garlic clove>garlic clove. Dimethyl phthalate (DMP), diethyl phthalate (DEP), diisobutyl phthalate (DIBP), DBP, and DEHP were the main PAEs species and were detected in all the surface soils collected from Pizhou City. Compared with the soil allowable concentrations of the six PAEs in the United States, the DMP and DBP concentrations in approximately 100% and 63.2% of soil samples exceeded the recommended allowable concentrations set by the EPA. However, the levels of DEP, DIBP, and DEHP in the soils were below the maximum allowable concentrations set by the EPA. Nevertheless, the average content of DEHP in soils was 486 µg·kg-1 and was found to be much higher than that in the other four PAEs. Six PAEs, including DMP, DEP, DIBP, DBP, butyl benzyl phthalate (BBP), and DEHP, were detected in all the agricultural film samples. Among them, the contents of DBP and DEHP in the agricultural films were the highest, accounting for 53.7%-63.2% of the total PAEs. The amount of PAEs present in the residual film was significantly lower than that in the new film, and all six PAEs were detected in garlic or soil samples, suggesting that agricultural film can be an important source of PAEs in garlic farming soils and garlic. Furthermore, the garlic plants absorbed DMP and DEP efficiently from the substrate and showed higher translocation factors (TFs) for DMP and DEP than those for DBP, BBP, DEHP, and di-n-octyl phthalate (DnOP), resulting in a higher accumulation of DMP and DEP in the over-ground parts of garlic. In contrast, DBP and BBP in roots of garlic displayed higher bioconcentration factors (57.4 and 81.5, respectively) compared to those of the other four PAEs, whereas the TFs of DBP and BBP were lower; this may have contributed to the high accumulation of DBP in garlic bulbs. The BCFs and TFs of DEHP and DnOP in garlic were relatively lower, but the DEHP had been detected in all garlic cloves, which may be a result of the higher DEHP contents in soils.

Metabolomic Analysis Reveals the Effect of Insecticide Chlorpyrifos on Rice Plant Metabolism.

Pesticides as important agricultural inputs play a vital role in protecting crop plants from diseases and pests; however, the effect of pesticides on crop plant physiology and metabolism is still undefined. In this study, the effect of insecticide chlorpyrifos at three doses on rice plant physiology and metabolism was investigated. Our results revealed that chlorpyrifos cause oxidative stress in rice plants and even inhibit plant growth and the synthesis of protein and chlorophyll at high doses. The metabolomic results suggested that chlorpyrifos could affect the metabolic profiling of rice tissues and a total of 119 metabolites with significant changes were found, mainly including organic acids, amino acids, lipids, polyphenols, and flavonoids. Compared to the control, the content of glutamate family amino acids were significantly disturbed by chlorpyrifos, where defense-related proline and glutathione were significantly increased; however, glutamic acid, N-acetyl-glutamic acid and N-methyl-glutamic acid were significantly decreased. Many unsaturated fatty acids, such as linolenic acid and linoleic acid, and their derivatives lysophospholipids and phospholipids, were significantly accumulated in chlorpyrifos groups, which could act as osmolality substances to help rice cells relieve chlorpyrifos stress. Three organic acids, aminobenzoic acid, quinic acid, and phosphoenolpyruvic acid, involved in plant defenses, were significantly accumulated with the fold change ranging from 1.32 to 2.19. In addition, chlorpyrifos at middle- and high-doses caused the downregulation of most flavonoids. Our results not only revealed the effect of insecticide chlorpyrifos on rice metabolism, but also demonstrated the value of metabolomics in elucidating the mechanisms of plant responses to stresses.

Effects of chlorpyrifos on the metabolic profiling of Bacillus megaterium strain RRB.

Many microorganisms have been reported to degrade organic pollutants in the environment and plants, however, the specific information about the effect of organic pollutants on the metabolism of microorganisms is poorly investigated. In the present study, the effect of the pesticide chlorpyrifos on the metabolic profiling of Bacillus megaterium strain RRB was investigated using metabolomics. Our data show that chlorpyrifos acting as an energy source was readily concentrated in the strain RRB from the culture medium. During early cultivation, the shift in energy sources from tryptic soy broth to chlorpyrifos may temporarily cause the strain RRB to enter the starvation stage, where some synthesis-related amino acids and intermediates in the pathways of TCA cycle and pyridoxine metabolism were decreased. The increase of nucleotides and lysine may help the strain RRB cope with the starvation stage. During later cultivation, many metabolites including organic acids, nucleosides and sugar phosphates were gradually accumulated, which indicates that chlorpyrifos could be utilized by the stain RRB to generate metabolites bacteria needed. In addition, arginine acting as a nitrogen-storage amino acid was gradually decreased with later cultivation, suggesting that chlorpyrifos could not provide enough nitrogen for bacteria.

Isolation, characterization and application of the epoxiconazole-degrading strain Pseudomonas sp. F1 in a soil-vegetable system.

Epoxiconazole (EPX) has a long half-life in soil and causes various toxicological effects in both the ecosystem and mammals. In this study, eight strains of bacteria capable of degrading EPX were isolated from pesticide-contaminated soil, with strain F1 showing the best effect. This strain was identified as Pseudomonas sp. by 16S rRNA gene sequencing and physiological-biochemical analyses. Our results indicated that strain F1 has a high capacity to degrade EPX, removing 92.1% of EPX within 6 days. The temperature and pH were the two most important environmental factors affecting EPX degradation, followed by substrate concentration and inoculum dose. In addition, strain F1 has a high capacity to promote EPX degradation in soils, with a lower t1/2 value (2.64 d) in F1-inoculated soil compared to the control (t1/2 = 96.3 d) without strain F1. The strain could efficiently colonize rhizosphere soil and enhance degradation of EPX, leading to a significant decrease in the accumulation and translocation of EPX in vegetables, thereby alleviating the effects of EPX-induced stress on plants. Moreover, we observed that strain F1-gfp was able to colonize the roots, stems and leaves of Brassica rapa var. chinensis. Such colonization may play a role in the efficient degradation of EPX within plants. To our knowledge, this is the first study to demonstrate biodegradation of EPX in a soil-vegetable system using an EPX-degrading bacterium. This study indicates that strain F1 is a promising candidate for simultaneous bioremediation of soil contaminated with EPX and safe food production.

Multiomics analysis reveals that peach gum colouring reflects plant defense responses against pathogenic fungi.

In the present study, the differences in the antioxidant capability, metabolite composition and fungal diversity in peach gum with various colours were investigated. Metabolomics revealed that peach gum comprised many small-molecule metabolites (including primary and secondary metabolites), and most polyphenols (such as flavonoids and phenolic acids) showed a significantly positive relationship with the colour deepening, total phenol content and antioxidant capability. Using fungal diversity analysis, the abundance of five fungi at the genus level increased with peach gum colour deepening, and these fungi demonstrated a significantly positive relationship with two defense hormones (salicylic acid and abscisic acid) and most polyphenols (particularly flavonoids). The gummosis pathogenic fungus Botryosphaeria was among the five fungi, suggesting that peach gum colouring may reflect plant defense responses against pathogenic fungi. Additionally, the concentrations of 12 flavonoids in peach gum samples were detected based on LC-QQQ/MS, among which hesperetin, naringenin and eriodictyol were the most abundant.

Biodegradation of dibutyl phthalate by a novel endophytic Bacillus subtilis strain HB-T2 under in-vitro and in-vivo conditions.

The environmental prevalence and potential toxicity of dibutyl phthalate (DBP) motivate the attempt to develop feasible strategies to deal with DBP contamination. In this study, a strain of endphytic bacteria HB-T2 was isolated from sorrel roots and identified as Bacillus sp. by analysing its morphology, physiology, biochemistry and 16S rDNA sequence. The degradation efficiency of DBP by HB-T2 was almost identical under the temperature of 30∼40°C, but was significantly enhanced as the culture pH and inoculum size increases from 6.0 to 8.0, and 1% to 5% respectively. The degradation kinetics of DBP could be well described by the first-order kinetic model, with the degradation half-life ranging from 1.59 to 7.61 h when the initial concentrations of DBP were in the range of 5-20 mg/L. LC-MS analysis of the culture samples taken at varying intervals revealed monobutyl phthalate, phthalic acid and protocatechuic acid as the major metabolic intermediates during the degradation process. HB-T2 exhibited an excellent capability to degrade a wide range of phthalate esters (PAEs), especially butyl benzyl phthalate (BBP), dipentyl phthalate (DPP), and diisobutyl phthalate (DIBP). Inoculation of HB-T2 into Chinese cabbage (Brassica chinensis L.) growing in DBP-contaminated soils could significantly reduce the DBP levels in plant tissues and relieve the phytotoxic effects of DBP. Results of this study highlighted the great potential of this novel endophytic Bacillus subtilis strain HB-T2 for bioremediation of PAEs contamination and improvement of agricultural product safety by reducing PAEs accumulation in edible crops.

Application of an Endophyte Enterobacter sp. TMX13 to Reduce Thiamethoxam Residues and Stress in Chinese Cabbage (Brassica chinensis L).

A strain of thiamethoxam-degrading endophyte, named TMX13, was isolated from roots of mulberry (Morus alba L.) and was identified as Enterobacter sp. Inoculating Chinese cabbage (Brassica chinensis L) with strain TMX13-gfp (gfp-labeled TMX13) could significantly reduce thiamethoxam residues in the aboveground part (edible portion) of the vegetable. The theoretical daily intake (TDI) of thiamethoxam via consumption of TMX13-gfp inoculated Chinese cabbage was 0.17 µg/kg body weight per day, far less than the prescribed acceptable daily intake (ADI) for this pesticide. TMX13-gfp colonization could increase the leaf chlorophyll content and plant biomass and promote the development of plant roots. Compared with the uninoculated treatment, the contents of malondialdehyde (MDA) and hydrogen peroxide (H2O2) and the activity of superoxide dismutase (SOD) in leaves of the TMX13-gfp inoculated plants decreased by 18.4%-60.2%, suggesting that TMX13-gfp colonization could alleviate the oxidative stress induced by thiamethoxam exposure. The total amounts of organic acids and amino acids in root exudates from the TMX13-gfp inoculated Chinese cabbage decreased by 9.2% and 85.2%, respectively. Results of this study lead to the conclusion that the isolated endophyte Enterobacter sp. TMX13 could reduce thiamethoxam residues in edible vegetables, promote plant growth, and alleviate the phytotoxic effects induced by thiamethoxam exposure.

Isolation, Colonization, and Chlorpyrifos Degradation Mediation of the Endophytic Bacterium Sphingomonas Strain HJY in Chinese Chives (Allium tuberosum).

The endophyte-plant interaction can benefit the host in many different ways. An endophytic bacterium strain (HJY) capable of degrading chlorpyrifos (CP) was isolated from Chinese chives (Allium tuberosum Rottl. ex Spreng). The isolated bacterium HJY classified as Sphingomonas sp. strain HJY could use CP as the sole carbon source. After being marked with the gfp gene, the colonization and distribution of strain HJY-gfp were directly observed in different tissues of Chinese chives with a confocal laser scanning microscope. The inoculation of strain HJY-gfp in Chinese chives resulted in a higher degradation of CP inside the plants than in uninoculated plants. With drench application, up to 70 and 66% of CP were removed from shoots and roots of inoculated Chinese chives, respectively. Moreover, up to 75% of CP was removed from the soil containing plants inoculated with HJY-gfp. With foliage application, the applied concentration of chlorpyrifos affected the degradation performance of strain HJY in Chinese chives. Significant differences were observed only between inoculated and uninoculated Chinese chives with the low applied concentration of CP. Together, other than natural endophyte-assisted plant protection for food safety, the interaction of HJY and plant may be also a promising strategy for in situ bioremediation of soil contaminated with CP.

Enhanced degradation of chlorpyrifos in rice (Oryza sativa L.) by five strains of endophytic bacteria and their plant growth promotional ability.

Endophytic bacteria reside in plant tissues, such as roots, stems, leaves and seeds. Most of them can stimulate plant growth or alleviate phytotoxicity of pollutants. There are handful species with dual functions stimulating plant growth and degrading pollutants have been reported. Five endophytic bacteria were isolated from chlorpyrifos (CP) treated rice plants and identified as Pseudomonas aeruginosa strain RRA, Bacillus megaterium strain RRB, Sphingobacterium siyangensis strain RSA, Stenotrophomonas pavanii strain RSB and Curtobacterium plantarum strain RSC according to morphological characteristics, physiological and biochemical tests, and 16S rDNA phylogeny. All of them possessed some plant growth promotional traits, including indole acetic acid and siderophore production, secretion of phosphate solubilization and 1-aminocyclopropane-1-carboxylate deaminase. The bacteria were marked with the green fluorescent protein (gfp) gene and successfully colonized into rice plants. All isolates were able to degrade CP in vitro and in vivo. The five isolates degraded more than 90% of CP in 24 h when the initial concentration was lower than 5 mg/L. CP degradation was significantly enhanced in the infested rice plants and rice grains. The final CP residual was reduced up to 80% in the infested rice grains compared to the controls. The results indicate that these isolates are promising bio-inoculants for the removal or detoxification of CP residues in rice plants and grains.

Conditions Optimizing and Application of Laccase-mediator System (LMS) for the Laccase-catalyzed Pesticide Degradation.

A high capacity of laccase from Trametes versicolor capable of degrading pesticides has been revealed. The conditions for degrading of five selected pesticides including chlorpyrifos, chlorothalonil, pyrimethanil, atrazine and isoproturon with the purified laccases from Trametes versicolor were optimized. The results showed that the optimum conditions for the highest activity were pH at 5.0 and temperature at 25 °C. The best mediators were violuric acid for pyrimethanil and isoproturon, vanillin for chlorpyrifos, and acetosyringone and HBT for chlorothalonil and atrazine, respectively. The laccase was found to be stable at a pH range from 5.0 to 7.0 and temperature from 25 to 30 °C. It was observed that each pesticide required a different laccase mediator concentration typically between 4.0-6.0 mmol/L. In the experiment, the degradation rates of pyrimethanil and isoproturon were significantly faster than those of chlorpyrifos, chlorothalonil and atrazine. For example, it was observed that pyrimethanil and isoproturon degraded up to nearly 100% after 24 hours while the other three pesticides just reached up 90% of degradation after 8 days of incubation.