Mechanisms of biochar assisted di-2-ethylhexyl phthalate (DEHP) biodegradation in tomato rhizosphere by metabolic and metagenomic analysis

New insights into rhizosphere bacterial community shaped by lettuce genotypes for divergent degradation efficiencies of phthalates

Rhizosphere dissipation of organic pollutants benefits safe utilization of the polluted agricultural soil. Nevertheless, dissipation variation of phthalates (PAEs) in rhizosphere among different vegetable genotypes and the related microbial mechanisms remain unknown. Here, twelve lettuce cultivars with different genetic relationships identified by 18S rRNA gene sequencing were cultivated in soil spiked with di-(2-ethylhexyl) phthalate (DEHP). Bacterial communities and function genes in rhizosphere of lettuce were analyzed by 16S rRNA gene and metagenomic sequencing. Results showed significant variations in DEHP concentrations of roots (2.8-15.3 mg/kg) and shoots (0.70-1.8 mg/kg) among 12 cultivars. Notably, cultivars L11 and L12 showed the lowest DEHP accumulation in roots and shoots, being lower by 82 % and 58 % than the highest accumulators (cultivars L5 and L6), respectively. This accumulation variation was closely connected with their genetic relationships and exhibited genotype-dependent trait. The significantly different bacterial community diversities and structures were recorded in rhizosphere among 12 cultivars. Especially, bacterial communities in rhizosphere of cultivars L11 and L12 (low-DEHP accumulators with high DEHP dissipation) strengthened their adaptation by enriching pollutant-resistant taxa, increasing extracellular polymeric substance contents and biofilm formation, as well as constructing complex ecological networks under DEHP pollution. Moreover, PAE-degrading bacteria and genes (e.g., hydrolase65, phtAb, and pcaI) in rhizosphere were enriched by low-DEHP accumulators, which benefited DEHP removal and subsequently safe agricultural products. This study provides new insights into microbial mechanisms on rhizosphere DEHP degradation and its correlation with accumulation variation among different crop genotypes.

Ecological effects of biochar in heavy metal-contaminated soils from multidimensional perspective: Using meta-analysis

The application of biochar in the remediation of heavy metal-contaminated soil shows great potential, but its comprehensive impacts on metal dynamics and the soil ecosystem have not been quantified. This study conducted a meta - analysis of 496 observations from 41 studies. The results indicated that biochar can significantly decrease the bioavailability of cationic metals, but has limited effect on anionic heavy metals. After application, soil nutrient content and enzyme activity significantly increased. Microbial network analysis revealed enhanced interactions between species, and the reconstruction of the core microbial community indicated a shift in microbial survival strategies from resisting heavy metal stress to nutrient cycling and plant symbiosis. FAPROTAX analysis showed that microbial communities related to nitrogen and sulfur cycles were significantly stimulated. This study explores the role of biochar in restoring soil multifunctionality while addressing metal pollution issues from multiple perspectives, offering key insights for developing targeted soil remediation strategies.

Dynamic impact of polyethylene terephthalate nanoplastics on antibiotic resistance and microplastics degradation genes in the rhizosphere of Oryza sativa L

This study examined the effects of polyethylene terephthalate (PET) nanoplastics on the rhizosphere of Oryza sativa L., focusing on dynamic changes and interactions among microbial communities, antibiotic resistance genes (ARGs) and microplastic degradation genes (MDGs). PET exposure altered the structure and function of soil microbial, enabling specific microbial groups to thrive in polluted environments. High-dose PET treatments markedly increased the abundance and dissemination of ARGs, primarily via resistance mechanisms such as antibiotic efflux and target alteration. By providing additional carbon sources and surfaces for microbial attachment, PET stimulated the growth of microorganisms harboring MDGs, resulting in an increase in MDGs abundance. The elevated expression of MDGs facilitated the propagation of ARGs, with overlapping host microorganisms suggesting that certain microbial groups exhibit dual metabolic capabilities, enabling them to endure both antibiotic and microplastic pressures. Toxic byproducts of microplastic degradation, such as mono-ethylhexyl phthalate, further promoted ARGs dissemination by increasing horizontal gene transfer frequency. Structural equation modeling revealed that PET indirectly influenced ARGs and MDGs expression by altering soil C/N ratio, available phosphorus, and enzyme activities. Thus, nanoscale PET exacerbates ecological risks to soil microbial communities by driving co-propagation of ARGs and MDGs, highlighting the persistent threat of composite pollution to agroecosystems.

Mechanistic and structural insights into EstS1 esterase: A potent broad-spectrum phthalate diester degrading enzyme

Phthalate diesters are important pollutants and act as endocrine disruptors. While certain bacterial esterases have been identified for phthalate diesters degradation to monoesters, their structural and mechanistic characteristics remain largely unexplored. Here, we highlight the potential of the thermostable and pH-tolerant EstS1 esterase from Sulfobacillus acidophilus DSM10332 to degrade high molecular weight bis(2-ethylhexyl) phthalate (DEHP) by combining biophysical and biochemical approaches along with high-resolution EstS1 crystal structures of the apo form and with bound substrates, products, and their analogs to elucidate its mechanism. The catalytic tunnel mediates entry and exit of the substrate and product, respectively. The centralized Ser-His-Asp triad performs catalysis by a bi-bi ping-pong mechanism, forming a tetrahedral intermediate. Mutagenesis analysis showed that the Met207Ala mutation abolished DEHP binding at the active site, confirming its essential role in supporting catalysis. These findings underscore EstS1 as a promising tool for advancing technologies aimed at phthalate diesters biodegradation.

Efficient remediation of di-(2-ethylhexyl) phthalate and plant-growth promotion with the application of a phosphate-solubilizing compound microbial agent

The ecotoxic endocrine-disrupting chemical di-(2-ethylhexyl) phthalate (DEHP) is ubiquitous in agricultural soil, posing a serious threat to human health. Here, we report efficient soil-borne DEHP degradation and plant growth promotion by a microbial organic fertilizer GK-PPB prepared by combining a recycled garden waste-kitchen waste compost product with ternary compound microbial agent PPB-MA, composed of Penicillium oxalic MB08F, Pseudomonas simiae MB751, and Bacillus tequilensis MB05B. The combination of MB08F and MB751 provided synergistic phosphorus solubilization, and MB05B enhanced the DEHP degradation capacity of MB08F via bioemulsification. Under optimal conditions (25.70 °C and pH 7.62), PPB-MA achieved a 96.81 % degradation percentage for 1000 mg L-1 DEHP within 5 days. The degradation curve followed first-order kinetics with a half-life of 18.24 to 24.76 h. A complete mineralization pathway was constructed after identifying the degradation intermediates of 2H-labeled DEHP. Evaluation in Caenorhabditis elegans N2 showed that PPB-MA eliminated the ecological toxicity of DEHP. A pakchoi (Brassica chinensis L.) pot experiment demonstrated that GK-PPB promoted phosphorus solubilization and plant growth, reduced soil DEHP residue, and decreased DEHP accumulation in pakchoi, suggesting its potential practical utility in environmentally responsible and safe cultivation of vegetables.