AUTHOR=Hu Yidan , Wang Yinghui , Han Xi , Shan Yawei , Li Feng , Shi Liang 

TITLE=Biofilm Biology and Engineering of Geobacter and Shewanella spp. for Energy Applications

JOURNAL=Frontiers in Bioengineering and Biotechnology

VOLUME=9

YEAR=2021

URL=https://www.frontiersin.org/journals/bioengineering-and-biotechnology/articles/10.3389/fbioe.2021.786416

DOI=10.3389/fbioe.2021.786416

ISSN=2296-4185

ABSTRACT=<p><italic>Geobacter</italic> and <italic>Shewanella</italic> spp. were discovered in late 1980s as dissimilatory metal-reducing microorganisms that can transfer electrons from cytoplasmic respiratory oxidation reactions to external metal-containing minerals. In addition to mineral-based electron acceptors, <italic>Geobacter</italic> and <italic>Shewanella</italic> spp. also can transfer electrons to electrodes. The microorganisms that have abilities to transfer electrons to electrodes are known as exoelectrogens. Because of their remarkable abilities of electron transfer, <italic>Geobacter</italic> and <italic>Shewanella</italic> spp. have been the two most well studied groups of exoelectrogens. They are widely used in bioelectrochemical systems (BESs) for various biotechnological applications, such as bioelectricity generation <italic>via</italic> microbial fuel cells. These applications mostly associate with <italic>Geobacter</italic> and <italic>Shewanella</italic> biofilms grown on the surfaces of electrodes. <italic>Geobacter</italic> and <italic>Shewanella</italic> biofilms are electrically conductive, which is conferred by matrix-associated electroactive components such as <italic>c</italic>-type cytochromes and electrically conductive nanowires. The thickness and electroactivity of <italic>Geobacter</italic> and <italic>Shewanella</italic> biofilms have a significant impact on electron transfer efficiency in BESs. In this review, we first briefly discuss the roles of planktonic and biofilm-forming <italic>Geobacter</italic> and <italic>Shewanella</italic> cells in BESs, and then review biofilm biology with the focus on biofilm development, biofilm matrix, heterogeneity in biofilm and signaling regulatory systems mediating formation of <italic>Geobacter</italic> and <italic>Shewanella</italic> biofilms. Finally, we discuss strategies of <italic>Geobacter</italic> and <italic>Shewanella</italic> biofilm engineering for improving electron transfer efficiency to obtain enhanced BES performance.</p>