PHYSIOLOGY/ELECTRON TRANSPORT A Novel Electrochemically Active and Fe(III)-reducing Bacterium Phylogenetically Related to Clostridium butyricum Isolated from a Microbial Fuel Cell Hyung Soo Park 1,w , Byung Hong Kim 1, *, Hyo Suk Kim 2 , Hyung Joo Kim 1 , GwangTae Kim 1 , Mia Kim 1 , In Seop Chang 1 , Yong Keun Park 2 and Hyo Ihl Chang 2 1 Water Environment Research Centre, Korea Institute of Science and Technology, Hawolgok-dong, Sungpook-ku, Seoul 136-791, Korea. 2 Graduate School of Biotechnology, Korea University, Anam-dong, Sungpook-ku, Seoul 136-701, Korea (Received 19 March 2001; accepted in revised form 31 August 2001) Key Words: Clostridium sp. EG3, dissimilatory Fe(III) reduction, cyclic voltammogram, electrochemically active bacteria, microbial fuel cell An obligatory anaerobic bacterium was isolated from a mediator-less microbial fuel cell using starch processing wastewater as the fuel and designated as EG3. The isolate was Gram-positive, motile and rod (2.8–3.0 mm long, 0.5–0.6 mm wide). The partial 16S rRNA gene sequence and analysis of the cellular fatty acids profile suggested that EG3 clusters with Clostridium sub-phylum and exhibited the highest similarity (98%) with Clostridium butyricum. The temperature and pH optimum for growth were 371C and 7.0, respectively. The major products of glucose and glucose/ Fe(O)OH metabolism were lactate, formate, butyrate, acetate, CO 2 and H 2 . Growth was faster at the initial phase and the cell yield was higher when the medium was supplemented with Fe(O)OH than without Fe(O)OH. These results suggest that Fe(III) ion is utilised as an electron sink. Cyclic voltammetry showed that Clostridium butyricum EG3 cells were electro- chemically active. It is a novel characteristic of strict anaerobic Gram- positive bacteria. # 2001 Academic Press Introduction Fe(III) is reduced by various bacteria through their respiratory, fermentative or photosynthetic metabolisms. Some of them are able to conserve energy for growth by coupling the oxidation of organic acids, aromatic hydrocarbons and H 2 to Fe(III) reduc- tion. These include species of the genera Geobacter [1,2], of the genera Shewanella [3,4] and a sulfate- reducing bacterium, Desulfotomacum reducens [5]. A fermentative bacterium, Clostridium beijerinckii, iso- lated from freshwater sediment, reduces Fe(III) as an electron sink during glucose metabolism [6]. In the metabolism of a photosynthetic bacterium, Rhodobacter *Address correspondence to: Byung Hong Kim, Fax: +82-2-958- 5839. E-mail: bhkim@kist.re.kr w Present address: R&D Centre, Samsung Engineering Co. 39-3, Songbok-Ri, Suji-Eup, Yongin-City, Kyonggi-Do, 449-844, Korea. 1075–9964/01/060297 + 10 $35.00/0 # 2001 Academic Press Anaerobe (2001) 7, 297–306 doi:10.1006/anae.2001.0399