Gluconacetobacter sp. NOK21 유래 섬유소막의 미생물연료전지에 이용 가능성

Abstract

Biological energy ATP generated on oxidative degradation of organic matters is converted into electrical energy in microbial fuel cell(MFC) system. MFC is one of the methods for the production of sustainable clean energy. But it has some obstacles to overcome for the practical use, one of which is manufacture of cheap proton-exchange membrane. Utilization of biomembranes that is cheap though low in proton-selective permeability was considered in this study. Bacterial celluloses with hydrogel structures were expected to have high proton-selective permeability in contrast to plant celluloses with highly ordered crystalline structure. Gluconacetobacter species NOK21, a kind of acetic acid bacteria, was reported to form pellicles on the surface of liquid medium. The pellicle membranes were investigated for their potential uses as an alternative to proton exchange membranes in MFC system. The strain, G. species NOK21, was not different from G. hansenii with respect to cell shape and size, and physiological characteristics. This supports the previous report that 1,380bp nucleotide sequences of 16S-rRNA gene from the G. species NOK21 showed above 99.7% similarity to many strains belonging to G. hansenii. G. species NOK21 synthesized pellicles in the liquid medium containing 1~3% ethanol but not in the medium containing above 4% ethanol due to the tolerance limit of toxicity. Meanwhile glucose in the medium promoted pellicle synthesis in the range of 1%-5% concentrations, the maximum concentration 1.4877 g/L was obtained at 5%. Addition of ethanol to the liquid medium containing glucose increased the concentration of celluosic pellicles. Solid state 13C-NMR analysis of the pellicle revealed that its main body was a glucose polymer like a cellulose fiber and it has some carboxylate(COO-) carbons. The bacterial pellicle through scanning electron microscopy(SEM) was shown to have multiple layers of net-like structures with random organization of cellulose fibers. The pellicle membrane maintained hydrogel property with high water content. Even though its physical strength was weaker than commercial cation exchanger membrane Neosepta CMX, it can be improved by conditioning bacterial cultures. Positive data for the use of the bacterial cellulosic membranes in MFC was that the bacterial membrane had about 3-fold higher efficiency than plastic membrane Neosepta CMX in generation of electricity. MFC with dual chamber system constructed for this study responded normally to the change of anode surface area, the presence of electron mediator and aeration. Moreover 150~200 mW/m2 (per anode surface area) of electrical power was generated stably in our MFC which had bacterial cellulosic membranes as proton exchange membranes. The power was considerable in comparison with those 18-3,600 mW/m2 that were obtained by other researchers under similar conditions. This study opened for the first time the possible use of bacterial celluloses from G. species NOK21 as an alternative to the proton exchange membrane in MFC.