Guo Yuxin

Bio: Guo Yuxin is an academic researcher from South China Agricultural University. The author has contributed to research in topics: Tetramethrin & Pyrethroid. The author has an hindex of 1, co-authored 2 publications receiving 2 citations.

Novel Mechanism and Kinetics of Tetramethrin Degradation Using an Indigenous Gordonia cholesterolivorans A16.

Abstract: Tetramethrin is a pyrethroid insecticide that is commonly used worldwide. The toxicity of this insecticide into the living system is an important concern. In this study, a novel tetramethrin-degrading bacterial strain named A16 was isolated from the activated sludge and identified as Gordonia cholesterolivorans. Strain A16 exhibited superior tetramethrin degradation activity, and utilized tetramethrin as the sole carbon source for growth in a mineral salt medium (MSM). High-performance liquid chromatography (HPLC) analysis revealed that the A16 strain was able to completely degrade 25 mg·L-1 of tetramethrin after 9 days of incubation. Strain A16 effectively degraded tetramethrin at temperature 20-40 °C, pH 5-9, and initial tetramethrin 25-800 mg·L-1. The maximum specific degradation rate (qmax), half-saturation constant (Ks), and inhibition constant (Ki) were determined to be 0.4561 day-1, 7.3 mg·L-1, and 75.2 mg·L-1, respectively. The Box-Behnken design was used to optimize degradation conditions, and maximum degradation was observed at pH 8.5 and a temperature of 38 °C. Five intermediate metabolites were identified after analyzing the degradation products through gas chromatography-mass spectrometry (GC-MS), which suggested that tetramethrin could be degraded first by cleavage of its carboxylester bond, followed by degradation of the five-carbon ring and its subsequent metabolism. This is the first report of a metabolic pathway of tetramethrin in a microorganism. Furthermore, bioaugmentation of tetramethrin-contaminated soils (50 mg·kg-1) with strain A16 (1.0 × 107 cells g-1 of soil) significantly accelerated the degradation rate of tetramethrin, and 74.1% and 82.9% of tetramethrin was removed from sterile and non-sterile soils within 11 days, respectively. The strain A16 was also capable of efficiently degrading a broad spectrum of synthetic pyrethroids including D-cyphenothrin, chlorempenthrin, prallethrin, and allethrin, with a degradation efficiency of 68.3%, 60.7%, 91.6%, and 94.7%, respectively, after being cultured under the same conditions for 11 days. The results of the present study confirmed the bioremediation potential of strain A16 from a contaminated environment.

Degradation bacterium for pyrethroid insecticides and application thereof

Abstract: The invention discloses a degradation bacterium for pyrethroid insecticides and application thereof. The invention finds out that Staphylococcus succinus has a degradation effect on various pyrethroidinsecticides such as d-cyphenothrin, permethrin, allethrin, bifenthrin, tetramethrin and chlorempenthrin for the first time, and a Staphylococcus succinus strain HLJ-10 which can effectively degradethe pyrethroid insecticides including d-cyphenothrin and the like is obtained by screening. On the basis of this invention, Staphylococcus succinus has a remarkable biodegradation effect on the pyrethroid insecticides including d-cyphenothrin and the like, can effectively degrade pyrethroids in a relatively wide pH value, temperature and concentration range, and can be used for repairing pollutedenvironments including water bodies, soil and the like polluted by the pyrethroid insecticides including d-cyphenothrin and the like. According to the degradation bacterium disclosed by the invention,a new development way is provided for breaking through an existing bottleneck in an existing process for managing pesticide residue caused pollution, a germplasm resources pool of the pesticide degradation bacteria is enriched and the application prospect is wide.

Indigenous bacterial consortium-mediated cypermethrin degradation in the presence of organic amendments and Zea mays plants.

Abstract: Cypermethrin is a toxic pyrethroid insecticide that is widely used in agricultural and household activities. One of the most serious issues is its persistence in the environment, because it is easily transported to the soil and aquatic ecosystem. The biodegradation of cypermethrin is emerging as an environmentally friendly method for large-scale treatment. This study examined the application of a novel binary bacterial combination-based (Bacillus thuringiensis strain SG4 and Bacillus sp. strain SG2) approach used for the enhanced degradation of cypermethrin from the environment. The bacterial strains degraded cypermethrin (80% and 85%) in the presence of external nitrogen sources (KNO3 and NaNO3). Furthermore, when immobilized in agar disc beads, the co-culture degraded cypermethrin (91.3%) with a half-life (t1/2) of 4.3 days compared to 4.9 days using sodium alginate beads. Cereal straw, farmyard manure, press mud compost, fresh cow dung, and gypsum were used as organic amendments in the soil to stimulate cypermethrin degradation. Cereal straw promoted the fastest cypermethrin degradation among the different organic amendments tested, with a t1/2 of 4.4 days. The impact of cypermethrin-degrading bacterial consortium on cypermethrin rhizoremediation was also investigated. Bacterial inoculums exhibited beneficial effects on plant biomass. Moreover, Zea mays and the bacterial partnership substantially enhanced cypermethrin degradation in soil. Six intermediate metabolites were detected during the degradation of cypermethrin, indicating that cypermethrin could be degraded first by the hydrolysis of its carboxyl ester bond, followed by the cleavage of the diaryl linkage and subsequent metabolism. Our findings highlight the promising potential and advantages of the bacterial consortium for the bioremediation of a cypermethrin-contaminated environment.

Novel mechanism and degradation kinetics of allethrin using Bacillus megaterium strain HLJ7 in contaminated soil/water environments.

Abstract: As a common pyrethroid insecticide, allethrin is widely used for various purposes in agriculture and home applications. At present, allethrin residues have been frequently detected worldwide, yet little is known about the kinetics and degradation mechanisms of this insecticide. In this study, a highly efficient allethrin-degrading bacterium, Bacillus megaterium strain HLJ7, was obtained through enrichment culture technology. Strain HLJ7 can remove 96.5% of 50 mg L-1 allethrin in minimal medium within 11 days. The first-order kinetic analysis of degradation demonstrated that the half-life of allethrin degradation by strain HLJ7 was 3.56 days, which was significantly shorter than the 55.89 days of the control. The Box-Behnken design of the response surface method optimized the degradation conditions for strain HLJ7: temperature 32.18 °C, pH value 7.52, and inoculation amount 1.31 × 107 CFU mL-1. Using Andrews equation, the optimal concentration of strain HLJ7 to metabolize allethrin was determined to be 21.15 mg L-1, and the maximum specific degradation rate (qmax), half-rate constant (Ks) and inhibition coefficient (Ki) were calculated to be 1.80 d-1, 1.85 mg L-1 and 68.13 mg L-1, respectively. Gas chromatography-mass spectrometry identified five intermediate metabolites, suggesting that allethrin could be degraded firstly by cleavage of its carboxylester bond, followed by degradation of the five-carbon ring and subsequent metabolism. The results of soil remediation experiments showed that strain HLJ7 has excellent bioremediation potential in the soils. After 15 days of treatment, about 70.8% of the initial allethrin (50 mg kg-1) was removed and converted into nontoxic intermediate metabolites, and its half-life was significantly reduced in the soils. Taken together, these findings shed light on the degradation mechanisms of allethrin and also highlight the promising potentials of B. megaterium HLJ7 in bioremediation of allethrin-comtaminated environment.

Systems biology analysis of pyrethroid biodegradation in bacteria and its effect on the cellular environment of pests and humans

Abstract: Pyrethroid insecticides are widely used to manage crop and household pests. The extensive use of pyrethroids leads to pesticide resistance in insects and negatively affects human health. Microbial degradation of pyrethroids is an emerging method to minimize their off-target toxic effects on the environment. The main aim of this research work to compare the biomagnification of pyrethroids in different living systems in environment. This study performed a detailed analysis of pyrethroid biodegradation and toxicity using an in silico approach. Pyrethroid biodegradation was studied using a systems biology-based approach that correlated human, insect and microbial systems to achieve a comprehensive view of total environmental pyrethroid biomagnification and bioremediation. The topology of the pyrethroid model was determined using the hub nodes in cytoscape that improved the understanding of pyrethroid biodegradation and environmental losses. The results of the simulated model were used for the real-time analysis of metabolites, genes, RNA and enzymes in bacteria, insect and human cells. The model predicted the pyrethroid biochemistry and physiology in three living systems. The findings of this study elucidated the systems biology-based analysis of the effects of pyrethroids on bacterial, insect and human systems.

Identification of FadT as a Novel Quorum Quenching Enzyme for the Degradation of Diffusible Signal Factor in Cupriavidus pinatubonensis Strain HN-2

Abstract: Quorum sensing (QS) is a microbial cell–cell communication mechanism and plays an important role in bacterial infections. QS-mediated bacterial infections can be blocked through quorum quenching (QQ), which hampers signal accumulation, recognition, and communication. The pathogenicity of numerous bacteria, including Xanthomonas campestris pv. campestris (Xcc), is regulated by diffusible signal factor (DSF), a well-known fatty acid signaling molecule of QS. Cupriavidus pinatubonensis HN-2 could substantially attenuate the infection of XCC through QQ by degrading DSF. The QQ mechanism in strain HN-2, on the other hand, is yet to be known. To understand the molecular mechanism of QQ in strain HN-2, we used whole-genome sequencing and comparative genomics studies. We discovered that the fadT gene encodes acyl-CoA dehydrogenase as a novel QQ enzyme. The results of site-directed mutagenesis demonstrated the requirement of fadT gene for DSF degradation in strain HN-2. Purified FadT exhibited high enzymatic activity and outstanding stability over a broad pH and temperature range with maximal activity at pH 7.0 and 35 °C. No cofactors were required for FadT enzyme activity. The enzyme showed a strong ability to degrade DSF. Furthermore, the expression of fadT in Xcc results in a significant reduction in the pathogenicity in host plants, such as Chinese cabbage, radish, and pakchoi. Taken together, our results identified a novel DSF-degrading enzyme, FadT, in C. pinatubonensis HN-2, which suggests its potential use in the biological control of DSF-mediated pathogens.