## 1 Introduction  
Using a microbial fuel cell (MFC) as a bio-electrochemical system is an alternative power source that directly converts chemical energy in organic matter to electrical energy through the biological ability of electrochemically active bacteria to donate electrons to conductive materials [1; 2; 3]. Bacteria that can efficiently couple to electrodes are called electricigens [4]. These electricigens naturally transfer electrons to an electrode in three ways: (i) electron transfer via bacteria-produced redox-active molecules (electron shuttles), (ii) short-range direct electron transfer between cytochromes on the outer membrane and the electrode; and (iii) long-range electron transport through conductive biofilms consisting of an extracellular matrix and motility apparatus (i.e., pili and filament) [1]. Besides, extracellular electron transfer efficiency is dependent on the ability of bacteria to migrate toward and colonize insoluble electron acceptors (electrodes) [5]. Although both Gram-negative and Gram-positive bacteria have the ability to generate electrical energy, favorable electricigens such as _Geobacter_ sp. and _Shewanella_ sp. are Gram-negative [1], while Gram-positive bacteria have a thicker, less-conductive membrane, making them much less electroactive. Thus, Gram-positives are capable of mediated electron transfer through exogenous mediators that are either present in the environment or added artificially [4]. _Corynebacterium_ species are one example of Gram-positive electricigens that have been applied in the presence of exogenously-added mediators. Recently, [PERSON] et al. reported that a small electricity output (a maximum power density of 7.3 mW m\({}^{-2}\)) by _Corynebacterium_ species (strain MFC03) was observed without any soluble redox mediator. However, when supplemented with the artificial redox mediator anthroquinone-2,6-disulfonate (AQDS), the maximum power density was drastically enhanced from 7.3 mW m\({}^{-2}\) to 41.8 mW m\({}^{-2}\)[6]. _C. glutamicum_, an important Gram-positive industrial bacterium, can utilize oxygen as a preferable terminal electron acceptor in its respiratory system [7; 8; 9]. Manipulation of the redox metabolism of _C. glutamicum_ connected with a cathode in a bio-electrochemical reactor system resulted in higher yields of the target product (l-lysine) when supplemented with AQDS [10]. Such results suggest that direct electron transfer between _C. glutamicum_ and an electrode might be difficult. To overcome this difficulty, anode surface modification using biocompatible and functional substrates with exogenous redox mediators has been considered. To enhance electrical communication between bacteria and an electrode, several polymer materials, such as nafion, polyamine, and polyaniline, have been used to fabricate anodes in MFCs [11; 12]. Among them, chitosan, a linear aminopolsaccharide, has attracted interest for its unique chemical functionalities (polycationic and nucleophilic properties) that are suitable for building of a bio-electrode interface. For instance, chitosan can transit from a soluble to insoluble form by a change in pH, can yield a 3-dimensional hydrogel network, and can interact with other functional groups via its amino and hydroxyl groups [13]. Moreover, anodic electron transfer can also be enhanced by suitable redox mediators for bacteria [2]. In the present study, we explored the ability of _C. glutamicum_ to transfer electrons to anode materials by electrochemical and metabolite analyses. In order to promote electrical communication across the bio-electrode interface, the carbon-based anode material was modified by chitosan hydrogel. Additionally, the chitosan hydrogel was chemically branched with an exogenous redox mediator, a ferrocene (Fc) derivate, to enhance the mediated electron transfer from the bacteria to the electrode (Figure 1) [4; 14]. Figure 1: Schematic representation of preparation of redox-hydrogen-modified electrode. (**A**) Chemical structure of ferrocene-branched chitosan redox hydrogel.