电子供体驱动希瓦氏菌还原钯的电子传递通路的研究

Palladium (Pd), as a precious metal, is indispensable in many high-tech industries, while its mineral reserve and supply is very limited. Due to this contradiction, the recovery and recycling of Pd from waste has become of particular interest. The process of bacterial reduction of Pd2+ to Pd0 (bio-Pd) is promising as Pd recovery technology from wastewater as well as a method to synthesize nanoscale catalyst of Pd. For most bacteria, formate is the most effective electron donor for Pd2+ reduction compared with other electron donors, which causes some problems during applications. The mechanism under such a difference effect on Pd2+ reduction is unclear. Therefore, this study will investigate the electron transfer pathway for Pd2+ reduction by Shewanella oneidensis MR-1 in the presence of formate, pyruvate and lactate, respectively. Meanwhile, the membranous proteome and transcriptome will be analyzed under same conditions. Comparing these results, genes which might contribute to the different performance of three electron donors in Pd2+ reduction will be selected and verified for their role in Pd2+ reduction. In summary, this study aims to explore the molecular mechanism under different performance of Pd2+ reduction driving by different electron donors, and provide candidate targets for genetic modification to improve Pd2+ reduction by S. oneidensis MR-1 as well as other bacteria.

贵金属钯(Pd)在诸多高科技行业不可或缺但资源供给匮乏，导致回收和再利用Pd的技术受到关注。细菌还原Pd2+至Pd0纳米颗粒的过程，不仅可从废液中回收Pd，而且Pd0纳米颗粒还是多用途的催化剂，具有显著的应用价值。大多数细菌还原Pd2+的最优电子供体均为甲酸；导致应用中出现电子供体选择受限、操作繁琐、成本增加等诸多问题。因尚不清楚不同电子供体驱动下Pd2+还原的生物学机制，故本项目拟以典型的Pd2+还原细菌希瓦氏菌为对象：1) 解析分别以甲酸、丙酮酸和乳酸为电子供体时，从电子供体氧化至Pd2+还原的电子传递通路；2) 结合这三种电子供体条件下， Pd2+还原过程的膜蛋白组和转录组分析，寻找并验证差异节点对Pd2+还原的影响。最终，探索不同电子供体影响Pd2+还原的生物机制，为从生理和遗传角度调控希瓦氏菌的Pd2+还原过程提供理论依据，也为其它细菌还原Pd2+的研究和应用提供参考模型。

贵金属钯应用广泛但资源匮乏。希瓦氏菌具有很强的还原钯离子的能力，可实现从液体中回收钯；所合成的钯纳米颗粒具有优良的催化性能。作为生物还原过程，希瓦氏菌氧化电子供体并将电子最终传递给钯离子的过程尚不清晰，不同的电子供体为何导致差异极大的钯还原速率也不清楚。这些问题导致无法根据应用需求，调整希瓦氏菌还原钯离子合成钯纳米颗粒的过程。针对这些问题，本项目展开研究并发现乳酸、丙酮酸和甲酸作为电子供体时钯离子还原的终端还原酶不同，因此所合成的钯纳米离子在细胞的定位不同，导致催化性能也不同。此外，研究还发现丙酮酸与常用电子供体乳酸相比，能极大提高钯还原速率。比较丙酮酸和乳酸条件下的转录组发现，钯还原的两类终端还原酶以及甲酸脱氢酶在丙酮酸条件下的表达均显著上调，是丙酮酸增强钯离子还原的关键原因之一。这些研究结果为优化希瓦氏菌合成钯纳米颗粒的过程奠定了良好基础。优化后的条件合成出的钯纳米颗粒，与希瓦氏菌协同展现出良好的催化活性；此外，希瓦氏菌合成出了石墨烯负载的钯-金双金纳米颗粒，同样具有良好的催化活性。这些研究结果先后发表于Applied and Environmental Microbiology, Applied Microbiology and Biotechnology, Chemosphere等SCI期刊共5篇，培养研究生7名。