以食品工業中之共培養菌相建構多菌相微生物燃料電池的濳力之探討

Abstract

永續發展目標 (SDGs) 是聯合國於 2015 年宣布的普遍目標。在 SDGs 中，隨著我們面 臨更加嚴峻的氣候、空氣污染和能源危機和人口壓力:乾淨衛生的水資源、便宜的 再生能源、永續都市及社群發展這些目標越來越受到重視。微生物燃料電池 (Microbial Fuel Cell, MFC)為一種再生能源，利用特定電活性微生物(electrogens)分解 各種有機物的同時獲取其產生之電子轉換成電能，起初 MFC 相關研究多用於污水、活性污泥之處理以及土壤復育;近期研究方向發展轉向微生物電催化的運用，致力於固碳、再生原料上。 微生物間的交互作用與廢水中含有的有機物種類是生物層面主要影響燃料電池效能的主因，MFC 的菌種來源可分為混合菌相與固定菌相，剛開始多直接使用廢水污泥 作為燃料電池的菌種來源屬於混合菌相，產電量穩定持久;到後期才發展出藉由特 殊的電化學環境篩選出具有產電能力的菌株，並以單一菌株或共培養的形式培養於 燃料電池中屬於固定菌相，透過研究共培養微生物燃料電池中個株菌種代謝物的消 長，使我們了解微生物之間如何配合彼此的代謝途徑達到交互補償(cross-feeding)的 情形，相較混合菌相更為簡單的系統除了方便建構微生物之間交互作用的網絡也可 以避免混合菌相中菌種間的競爭，使系統更有效率，但相對來說共培養的系統對於 不同種類的有機污染物的適應性就沒有原來的好。 另一方面現行的食品生技產業中已有許多成熟的共培養菌相系統，像是果醋產業所 使用到的酵母菌與醋酸菌的結合，韓式泡菜中使用三種乳酸菌作為發酵起始菌種等等，這些成功的案例不但在代謝路徑上有著互補的關係，同時也能產生諸多小分子 代謝物，具有被 MFC 模式物種 Shewanella oneidensis MR-1 進一步利用產電的淺力。 本研究以現行生技食品產業的共培養發酵系統與產電菌結合，期望建立能應對多樣 的污水，並維持良好的產電效能的微生物燃料電池。使用產電菌模式物種 Shewanella oneidensis MR-1(S. o. MR-1) 作為中心，因其能代謝多樣小分子有機物之能力，搭配釀醋所使用的酵母菌、醋酸菌共培養菌相形成共培養系統，以及其他食品工業菌種做結合，並以 S. o. MR-1 單一菌株及 S. o. MR-1 與 E. coli 共培養之燃料電池則作為對照組，紀錄不同菌相處理人工廢水所產生之開路電壓(open circuit voltage, OCV) 作為產電能力之依據。 結果顯示酵母菌、醋酸菌與 S. o. MR-1 的共培養組合 OCV 平均為 450 mV，其他多菌 相組別 OCV 平均則介於 650 至 700 mV，與對照組在統計上並無明顯差異，我們推估 可能是酸鹼值的改變、不同菌種間的平衡以及一些具有抑制產電反應的代謝物產生， 使得多菌相的 MFC 沒有達到預期中增強發電的效果。

The Sustainable Development Goals (SDGs) are universal goals announced by United Nations in 2015. Among SDGs, clean water, clean energy and sustainable cities are getting more awareness as we are facing more severe climate, air pollution and energy crisis while the population still growing around the world. The microbial fuel cell (MFC) is a promising technology to combat those challenges, which it utilized electroactive bacteria (EAB) to generate electricity and decompose the organic waste. In the beginning, the research about MFC originally focus on wastewater treatment and soil decontamination; recently, people change the direction to electrochemical biocatalysts for carbon fixation and valuable by- product production. The interaction between microbes and the types of organic matter contained in wastewater are the main factors affecting the efficiency of fuel cells at the biological level. The source of bacteria in MFC can be divided into mixed culture and pure culture. For those used wastewater sludge as direct inoculum which belongs to the mixed culture: the electricity production is stable and long-lasting; on the other hand, the strains with the ability to generate electricity were isolated by utilized special electrochemical environment, and cultivated in the fuel cell in the form of a single strain or co-culture which are the pure culture: by studying the fluctuation of the metabolites from each individual strains in the co-cultivation microbial fuel cell, we can understand how the microorganisms cooperate with each other's metabolic pathways to achieve cross-feeding. It also avoids the competition between bacterial species in the mixed culture, which is more efficient than the mixed culture, but the co-culture systems have less adaptability to different types of organic pollutants. On the other hand, ‘Fermentation’ has been developed for centuries, people use various of single strain and co-culture systems that produce valuable products from different ingredients. Like yeast and acetobacter for vinegar and several lactobacillus species for kimchi fermentation. It provides the opportunity to improve MFC system by combine the EAB with exist fermentation models as we assume that EAB could benefits by the various metabolites produced by fermented co-culture model. In this study, we try to build a multi-cultural MFC that has the ability to utilized various wastewater stream from food industry. MFC model organism Shewanella oneidensis MR-1 (S. o. MR-1) is selected as center to construct the cross-feeding network, candidate microbes include Bacillus spp., Acetobacter spp., yeast species and E. coli. The electricity productivity was estimated based on the open circuit voltage (OCV) of fuel cell for each group. The single strain and co-culture MFC system (S. o. MR-1, S. o. MR-1 * E. coli) were served as reference models. The results showed that the multi-cultural MFC with yeast, acetobacter and S. o. MR-1 had an average OCV around 450 mV, and other combination were about 650 to 700 mV, but is didn’t show significant improvement between control and experimental groups, the reason could be the pH value changes, balance of population of each species and some inhibitors for repressed the electricity production were synthesized during the operation.