Electrochemistry of newly isolated Gram-positive bacteria Paenibacillus lautus with starch as sole carbon source

Electroactive bacteria (EAB) produce bioelectricity to drive versatile energy and environment applications. However, most EABs only use simple carbon sources like acetate and lactate, and feeding complex organic substrate blooms the non-electroactive bacteria and degrades performance. In this study, a new EAB strain (Paenibacillus lautus EB1) that directly produces electricity in microbial fuel cell (MFC) with starch as sole substrate was isolated and identified. After optimizing MFC conditions, maximum current power densities of 22.5 +/- 0.5 mW/m(2) (carbon felt electrode) and 212.4 +/- 29.2 mW/m(2) (carbon brush electrode) were achieved, which were among the highest in MFC fed with starch. Moreover, electrochemical and HPLC analyses indicated this strain secreted diverse electron shuttles including riboflavin and another two unidentified electron shuttles to carry out the EET in the low and high electrode potential, respectively. In-depth kinetic analyses revealed that riboflavin based EET is relatively insufficient but can be promoted with exogenously added riboflavin, with a half-maximum-current concentration (K-c) of 4.89 mu M. Therefore, a new EAB member that directly use complex substrate starch for bioelectricity generation was identified, which extends the microbial inventory to develop MFC with diverse substrates.