Construction and comparison of synthetic microbial consortium system (SMCs) by non-living or living materials immobilization and application in acetochlor degradation

Exploration of the biodegradation pathway and enhanced removal of imazethapyr from soil by immobilized Bacillus marcorestinctum YN1

Excessive or inappropriate applications of imazethapyr cause severe ecological deteriorations and health risks in human. A novel bacterial strain, i.e., Bacillus marcorestinctum YN1, was isolated to efficiently degrade imazethapyr, with the degradation pathways and intermediates predicted. Protein mass spectrometry analysis identified enzymes in strain YN1 potentially involved in imazethapyr biodegradation, including methylenetetrahydrofolate dehydrogenase, carbon-nitrogen family hydrolase, heme degrading monooxygenase, and cytochrome P450. The strain YN1 was further immobilized with biochar (BC600) prepared from mushroom waste (i.e., spent mushroom substrate) by pyrolysis at 600 °C to evaluate its degrading characteristics of imazethapyr. Scanning electron microscope observation showed that strain YN1 was adsorbed in the rich pore structure of BC600 and the adsorption efficiency reached the maximum level of 88.02% in 6 h. Both energy dispersive X-ray and Fourier transform infrared spectroscopy analyses showed that BC600 contained many elements and functional groups. The results of liquid chromatography showed that biochar-immobilized strain YN1 (IBC-YN1) improved the degradation rate of imazethapyr from 79.2% to 87.4%. The degradation rate of imazethapyr by IBC-YN1 could still reach 81.0% in the third recycle, while the bacterial survival rate was 67.73% after 180 d storage at 4 °C. The treatment of IBC-YN1 significantly shortened the half-life of imazethapyr in non-sterilized soil from 35.51 to 11.36 d, and the vegetative growth of imazethapyr sensitive crop plant (i.e., Cucumis sativus L.) was significantly increased in soil remediated, showing that the inhibition rate of root length and fresh weight were decreased by 12.45% and 38.49% respectively. This study exhanced our understanding of microbial catabolism of imazethapyr, and provided a potential in situ remediation strategy for improving the soil environment polluted by imazethapyr.

Characterization of a novel esterase and construction of a Rhodococcus-Burkholderia consortium capable of catabolism bis (2-hydroxyethyl) terephthalate

Bis (2-hydroxyethyl) terephthalate (BHET) is one of the main compounds produced by enzymatic hydrolysis or chemical depolymerization of polyethylene terephthalate (PET). However, the lack of understanding on BHET microbial metabolism is a main factor limiting the bio-upcycling of PET. In this study, BHET-degrading strains of Rhodococcus biphenylivorans GA1 and Burkholderia sp. EG1 were isolated and identified, which can grow with BHET as the sole carbon source. Furthermore, a novel esterase gene betH was cloned from strain GA1, which encodes a BHET hydrolyzing esterase with the highest activity at 30 °C and pH 7.0. In addition, the co-culture containing strain GA1 and strain EG1 could completely degrade high concentration of BHET, eliminating the inhibition on strain GA1 caused by the accumulation of intermediate metabolite ethylene glycol (EG). This work will provide potential strains and a feasible strategy for PET bio-upcycling.

Enhanced degradation of phthalate esters (PAEs) by biochar-sodium alginate immobilized Rhodococcus sp. KLW-1

In this study, a new strain of bacteria, named Rhodococcus sp. KLW-1, was isolated from farmland soil contaminated by plastic mulch for more than 30 years. To improve the application performance of free bacteria and find more ways to use waste biochar, KLW-1 was immobilized on waste biochar by sodium alginate embedding method to prepare immobilized pellet. Response Surface Method (RSM) predicted that under optimal conditions (3% sodium alginate, 2% biochar and 4% CaCl₂), di (2-ethylhexyl) phthalate (DEHP) degradation efficiency of 90.48% can be achieved. Under the adverse environmental conditions of pH 5 and 9, immobilization increased the degradation efficiency of 100 mg/L DEHP by 16.42% and 11.48% respectively, and under the high-stress condition of 500 mg/L DEHP concentration, immobilization increased the degradation efficiency from 71.52% to 91.56%, making the immobilized pellets have strong stability and impact load resistance to environmental stress. In addition, immobilization also enhanced the degradation efficiency of several phthalate esters (PAEs) widely existing in the environment. After four cycles of utilization, the immobilized particles maintained stable degradation efficiency for different PAEs. Therefore, immobilized pellets have great application potential for the remediation of the actual environment.

Degradation strategies of pesticide residue: From chemicals to synthetic biology

The past 50 years have witnessed a massive expansion in the demand and application of pesticides. However, pesticides are difficult to be completely degraded without intervention hence the pesticide residue could pose a persistent threat to non-target organisms in many aspects. To aim at the problem of the abuse of pesticide products and excessive pesticide residues in the environment, chemical and biological degradation methods are widely developed but are scaled and insufficient to solve such a pollution. In recent years, bio-degradative tools instructed by synthetic biological principles have been further studied and have paved a way for pesticide degradation. Combining the customized design strategy and standardized assembly mode, the engineering bacteria for multi-dimensional degradation has become an effective tool for pesticide residue degradation. This review introduces the mechanisms and hazards of different pesticides, summarizes the methods applied in the degradation of pesticide residues, and discusses the advantages, applications, and prospects of synthetic biology in degrading pesticide residues.

Occurrence and risk assessment of three chloroamide herbicides in water and soil environment in northeastern, eastern and southern China

Chloroamide herbicides can cause adverse effects on nontarget organisms, but there is limited information about their occurrence in the environment of major cropland growing regions. In this study, a total of 1012 soil samples, 617 surface water samples and 737 groundwater samples were collected from 2020 to 2021 in three regions of China to evaluate the occurrence and risk of three important chloroamide herbicides alachlor, acetochlor and butachlor using the improved QuEChERS extraction method and high performance liquid chromatography-mass spectrometry. The results showed that residues of the three chloroamide compounds in surface water and groundwater ranged from 0.1 to 176.0 μg L^-1, of which acetochlor was frequently detected from surface water (17.5%). As for the soil, mass fraction was varied between 1.0 and 1540.3 μg kg^-1, similarly acetochlor had the highest detection frequency (49.6%). Timewise, the median mass fraction of selected chloroamide herbicides in soil in 2021 (7.8 μg kg^-1) was significantly lower than that in 2020 (10.9 μg kg^-1). Spatially, there were regional differences in the content of environmental residues, and the overall level of residues in the northeast was relatively high. The environmental risk assessment based on the improved Risk Quotient (RQ) method indicated that the selected herbicides were currently within an acceptable range for human health risks in the soil and water environment in various regions, but acetochlor and butachlor had contributed to the RQ values of fish and earthworms (0.01＜RQ＜0.1) in recent years, respectively, which might pose a certain risk of oral exposure to aquatic and terrestrial organisms. This study provides valuable data and ideas for the rational application, pollution control and environmental safety evaluation of chloroamide herbicides in China.