Enhanced Plant–microbe Remediation of PCBs in Soil using Enzyme Modification Technique Combined with Molecular Docking and Molecular Dynamics

The study on the enhanced mechanisms of the enzymes involved in plant absorption, plant degradation, and microbial mineralization in the remediation of soils contaminated with polychlorinated biphenyls (PCBs) is of great significance for the application of plant-microbe combined remediation technique in PCB-contaminated soils. The present study first used a combination of molecular docking and molecular dynamics methods to calculate the effects of the plant absorption enzyme, plant degradation enzyme, and microbial mineralization enzyme on the PCBs in the soil environment. A multifunctional plant degradation enzyme was constructed with three functional roles of absorption, degradation, and mineralization using amino acid sequence recombination and site-directed mutagenesis to modify the template of plant degradation enzyme. Finally, using the Taguchi experimental design-assisted molecular dynamics simulation method, the suitable external environmental conditions of plant-microbe combined remediation of the PCB­-contaminated soil were determined. In total, six multifunctional plant degradation enzymes were designed, which exhibited a significantly improved efficiency of PCB degradation. In comparison to the complex of plant absorption enzyme, plant degradation enzyme, and microorganism mineralization enzyme (6QIM-3GZX-1B85), the six multifunctional plant degradation enzymes exhibited significantly higher efficiency (2.10–2.38 times) in degrading the PCBs, with a maximum of 2.69 times under suitable external environmental conditions.

Additional carbon stabilization in temperate subsoils impeded by biogeochemical and hydraulic constraints

<p>Formation of mineral-associated organic matter (MAOM) is a decisive process in the stabilization of OM against rapid microbial decomposition and thus in the soils’ role as global carbon (C) sink. Sorption experiments of dissolved OM (DOM) repeatedly showed that particularly mineral subsoils have a large sorption capacity to retain more C. However, there is also an increasing body of literature, revealing an increasing output of dissolved organic C (DOC) from soils. Here, we investigated into this paradox in forest soil under beech by a combination of a field labelling experiment with <sup>13</sup>C-enriched litter with a unique DO<sup>13</sup>C and <sup>13</sup>CO<sub>2</sub> monitoring, an in-situ C exchange experiment with <sup>13</sup>C-coated minerals, and batch sorption experiments.</p><p>Within two years of <sup>13</sup>C monitoring, only 0.5% of litter-derived DO<sup>13</sup>C entered the subsoil, where it was only short-term stabilized by formation of MAOM but prone to fast microbial mineralization. The <sup>13</sup>C monitoring, sorption/desorption experiments in the laboratory, and also the in-situ C exchange on buried soil minerals revealed that there is a frequent exchange of DOM with native OM and a preferential desorption of recently retained OM. Hence, there appeared to be a steady-state equilibrium between C input and output, facilitated by exchange and microbial mineralization of an adopted microbial community. The remobilized OM was also richer in less sorptive carbohydrates. Along with transport of most of DOM along preferential paths, this further increased the discrepancy between laboratory-measured sorption capacities of subsoil and the actual C loading of minerals. Finally, the <sup>13</sup>C labeling experiments revealed that input of fresh litter-derived OM into subsoil may even mobilize old-soil derived OM. Hence, in the field different biogeochemical constraints are acting that prevent that the laboratory-based C sink can be reached in the field.  We conclude, that forest subsoils can hardly be considered as additional C sink, even at management options that increase DOC input to subsoil.</p>

Characterization Methods for the Effect of Microbial Mineralization on the Microstructure of Hardened C3S Paste

Microbial mineralization has a significant effect on the hydration process of cement-based materials. This paper mainly studied the characterization methods for hydration degree and hydration product of C3S in hardened paste under microbial mineralization. Quantitative X-ray diffraction (QXRD), thermogravimetric analysis (TG), Fourier transform infrared spectroscopy (FT-IR), and electron backscatter diffraction (EBSD) were used and compared. The results showed that microbial mineralization increased the hydration degree of T-C3S. QXRD and EBSD could be used to characterize the content of C3S, and there were few differences between the two methods. TG could accurately characterize the content of Ca(OH)2 and CaCO3 at different depths of the sample, and FT-IR could qualitatively characterize the presence of Ca(OH)2 and CaCO3.