Collaborative Research: Microbial Fuel Cell Optimization through Digital Microfluidic Electrochemistry in Single-Bacterial Drops

城市污水处理过程消耗大量能源。然而，如果有机废物可以转化为能量，那么进入废物处理过程的有机材料就有可能提供正能量的废水处理。许多生长在废水中的细菌可以被利用来消耗这些有机污染物来净化水，同时通过它们的新陈代谢产生电流。这些细菌被捆绑在一种叫做微生物燃料电池的装置的电极内，以收集电流作为电能。为了从微生物燃料电池中获得最大的功率输出，必须确定有多少种细菌在被组织成称为生物膜的复杂菌落时，协同将有机物转化为电能。该项目将在一种新型小型化培养系统中研究这种协同代谢，该培养系统能够进行高通量分析，以加速筛选过程。这种微型培养系统将能够从一滴培养物中测量单一细菌物种的代谢，以及许多细菌的小型混合菌落。这些信息将用于确定产生的电流和消耗的有机物如何取决于细菌类型，以及多种细菌之间的潜在协同作用。受此项目启发的教育活动以高中女生动手教学模块为特色，她们将构建一个简单的微生物燃料电池，为发光二极管（LED）或数字手表供电。希望这次活动能向高中女生说明可再生绿色能源和生物技术作为令人兴奋的未来职业选择的潜力。微生物燃料电池系统组件，包括电极、膜和细菌，必须精心设计以达到最佳的发电效果。该项目将重点研究电极内细菌的遗传优化。考虑到废水细菌生长的相互关联的方式，这种优化是具有挑战性的。为此，拟议的研究有两个主要目标。第一个目标是开发一个高通量数字微流控（DMF）平台，用于研究微生物燃料电池的代谢和电流演化，从单一种细菌或小菌落混合细菌。第二个目标是通过对单个细菌电子转移限制的高通量分析来优化细菌群落的高功率密度。DMF芯片将由液滴驱动电极、纳米结构电化学电极和隔离的片上微孔细胞培养室组成。液滴驱动电极将培养液滴沉积到微孔中，培养微孔内的纳米结构电极将能够检测单个细菌输出电流以及使用循环伏安法测量特定细胞培养物含量。已知消耗废水中的有机物并通过微生物电化学代谢过程将其转化为电流的细菌，包括P. aeruginosa, Geobacter （G. sulfreducens）和Shewanella (S. oneidensis)，将首先作为单种培养的模式外电菌进行研究。通过选择性地增加培养系统的复杂性和异质性，从分离的单一物种开始，到混合细菌菌落，可以更好地了解细菌之间的协同作用。通过本研究，也希望DMF芯片能够成为研究生物电化学活性细菌中电子传递过程的新工具。

Municipal wastewater treatment processes consume significant amounts of energy. However, the organic materials fed into the waste treatment process offer the potential for energy-positive waste water treatment if this waste organic material can be converted into energy. Many bacteria that grow in waste water can be harnessed to consume these organic contaminants to clean up the water and at the same time generate electrical current from their metabolism. These bacteria are bound within an electrode of a device called a microbial fuel cell to harvest this current as electrical power. To achieve maximum power output from microbial fuel cells, it must be determined how many species of bacteria, when organized into complex colonies known as biofilms, collaborate to convert organic matter into electricity. This project will study this collaborative metabolism within a novel miniaturized culture system capable of high-through analysis to accelerate the screening process. This miniature culture system will be capable of measuring metabolism of a single bacterial species, as well as in small mixed colonies of many bacteria, from a single drop of culture. This information will be used to determine how the electrical current produced and the organic matter consumed depends on bacterium type, as well as the potential synergy between many types of bacteria. The educational activities inspired by this project feature a hands-on teaching module for high school girls, who will build a simple microbial fuel cell to power a light-emitted diode (LED) or a digital watch. It is hoped this activity will illustrate to high school girls the potential of renewable green energy and biotechnology as exciting future career choices.The microbial fuel cell system components, which include electrodes, membranes, and bacteria, must be carefully engineered to achieve optimal power generation. This project will focus on genetic optimization of the bacteria within the electrode. This optimization is challenging given the interconnected manner in which wastewater bacteria grow. Towards this end, the proposed research has two primary objectives. The first objective is to develop a high-throughput digital microfluidic (DMF) platform for studying microbial fuel cell metabolism and electrical current evolution from single species of bacteria or small colonies of mixed bacteria. The second goal is to optimize the bacterial communities for high power density through high-throughput analysis of single bacterium electron transfer limitations. The DMF chip will be fabricated with droplet actuation electrodes, nanostructured electrochemical electrodes, and isolated on-chip microwell cell culture chambers. The droplet actuation electrode deposits a culture droplet into the microwell, and nanostructured electrodes within the culture microwell will enable the detection of single bacterium output current as well as measurement of specific cell culture contents using cyclic voltammetry. Bacteria known to consume organic matter in waste water and convert it into electrical current through microbioelectrochemical metabolic processes, including P. aeruginosa, Geobacter (G. sulfurreducens) and Shewanella (S. oneidensis) will first be studied as the model exoelectrogens in single species culture. By selectively increasing complexity and heterogeneity in the culture systems, beginning with isolated single species and moving to mixed bacterial colonies, a better understanding of the synergism among bacteria can be systematically determined. Through this study, it also is hoped that the DMF chip will become established as a new tool for studying electron transfer processes in bioelectrochemically-active bacteria.