University of Brescia, Dep. of Civil, Environmental, Architectural Engineering, and Mathematics, Via Branze 43, 25123, Brescia, Italy.
University of Milano-Bicocca, Dept. of Earth and Environmental Sciences -DISAT, Piazza Della Scienza 1, 20126, Milano, Italy.
Chemosphere. 2022 Nov;307(Pt 4):136126. doi: 10.1016/j.chemosphere.2022.136126. Epub 2022 Aug 23.
Environmental pollution by hydrophobic hydrocarbons is increasing, notably nowadays due to a large amount of industrial activity. Microbial electrochemical technologies (MET) are promising bio-based systems which can oxidize hydrophobic hydrocarbon pollutants and produce bioelectricity simultaneously. However, MET faces some issues in terms of soil remediation, including low mass transfer, limited electro-activity of anodes as electron acceptors, low bioavailability of hydrocarbons, and the limited activity of beneficial bacteria and inefficient electron transport. This study aims to investigate the role of the addition of rhamnolipid as an analyte solution to the MET to enhance the efficacy and concurrently solve the abovementioned issues. In this regard, a novel long chain of RL was produced by using low-cost carbon winery waste through non-pathogenic Burkholderia thailandensis E264 strains. Different doses of RL were tested, including 10, 50, and 100 mg/L. A maximum enhancement in the oxidation of hydrophobic hydrocarbons was found to be up to 72.5%, while the current density reached 9.5 Am-2 for the MET reactor having a dose of 100 mg/L. The biosurfactants induced a unique microbial enrichment associated with Geobacter, Desulfovibrio, Klebsiella, and Comamona on the anode surface, as well as Pseudomonas, Acinetobacter, and Franconibacter in soil MET, indicating the occurrence of a metabolic pathway in microbes working with the anode and soil bioelectrochemical remediation system. According to cyclic voltammetry analysis, redox peaks appeared, showing a minor shift in redox MET-biosurfactant compared to the bare MET system. Furthermore, the phytotoxicity of polluted soil to L. sativum seeds after and before MET remediation shows a decrease in phytotoxicity of 77.5% and 5% for MET-biosurfactant system and MET only, respectively. With MET as a tool, this study confirmed for the first time that novel long-chain RL produced from non-Pseudomonas bacteria could remarkably facilitate the degradation of petroleum hydrocarbon via extracellular electron transfer, which provides novel insights to understand the mechanisms of RL regulating petroleum hydrocarbon degradation.
环境污染中的疏水烃类物质日益增多，尤其是近年来，随着工业活动的大量增加，这种情况更加明显。微生物电化学技术（MET）是一种很有前途的生物基系统，可以同时氧化疏水烃类污染物并产生生物电能。然而，MET 在土壤修复方面存在一些问题，包括传质能力低、作为电子受体的阳极电活性有限、烃类的生物可利用性低、有益细菌的活性有限以及电子传递效率低。本研究旨在探讨添加鼠李糖脂作为分析物溶液来增强 MET 的功效并同时解决上述问题的作用。为此，通过非致病性 Burkholderia thailandensis E264 菌株利用低成本的酿酒厂废碳生产了一种新型长链 RL。测试了不同剂量的 RL，包括 10、50 和 100mg/L。结果发现，当 MET 反应器中的 RL 剂量为 100mg/L 时，疏水烃类的氧化最大增强率达到 72.5%，而电流密度达到 9.5 Am-2。生物表面活性剂在阳极表面诱导出一种独特的微生物富集，涉及 Geobacter、Desulfovibrio、Klebsiella 和 Comamona，以及土壤 MET 中的 Pseudomonas、Acinetobacter 和 Franconibacter，表明微生物与阳极和土壤生物电化学修复系统协同工作时发生了代谢途径。根据循环伏安法分析，出现了氧化还原峰，表明与裸 MET 系统相比，MET-生物表面活性剂系统的氧化还原峰略有偏移。此外，MET 修复前后污染土壤对 L. sativum 种子的植物毒性显示，MET-生物表面活性剂系统和仅 MET 的植物毒性分别降低了 77.5%和 5%。通过 MET 作为工具，本研究首次证实，非假单胞菌产生的新型长链 RL 可以通过细胞外电子转移显著促进石油烃的降解，这为理解 RL 调节石油烃降解的机制提供了新的见解。
