Magnetite Compensates for the Lack of a Pilin-Associated 1 c-Type Cytochrome in Extracellular Electron Exchange 1 2 3

1 Department of Microbiology, University of Massachusetts, Amherst, Massachusetts 7 01003, USA; 2 Key Laboratory of Coastal Biology and Utilization, Yantai Institute of 8 Coastal Zone Research, Chinese Academy of Sciences, Yantai, Shandong 264003, 9 China. 10 11 *For correspondence. Email: fhliu@yic.ac.cn; Tel. (+86) 535 2109268; Fax (+86) 535 12 2109000. 13 14 Running title: Magnetite compensates for the lack of OmcS. 15