Invited Paper BP-SuA3
Conductive Biofilms As Living Electronic Materials

Sunday, October 20, 2019, 3:40 pm, Room A120-121

Natural living conductive biofilms transport electrons between electrodes and cells, as well as among cells fixed within the film, catalyzing an array of reactions from acetate oxidation to CO₂reduction. Synthetic biology offers tools to modify or improve electron transport through biofilms, creating a new class of engineered living conductive materials. However, these applications are currently limited by a lack of understanding of the physiological constraints of the host bacterium (chassis) to properly and predictably express and orient electron transfer (ET) proteins (e.g. c-type cytochromes) in the cell membrane, the ability to rapidly screen a large number of constructs for different ET pathways, and a library of operationally relevant chassis strains. In this talk I will describe results demonstrating the use of a suite of highly-optimized small molecule sensors (Marionette) developed for control over E. colicellular processes and used here to control expression of the ShewanellaMtrCAB pathway, and accessory electron carriers, in Marinobacter atlanticus. Marionette sensors were transformed into M. atlanticusand assessed for expression of yellow fluorescent protein (YFP) after the addition of 7 different small molecules (choline, vanillin, naringenin, DAPG, cumate, tetracycline, and IPTG) during both planktonic growth and in biofilms. A broad dynamic range of YFP expression was observed similar to that demonstrated with E. coli. When YFP was replaced with ET proteins, expression of MtrCAB led to an increase in current compared to the wild type strain when induced prior to inoculation into a bioelectrochemical system (BES). However, the effect was not robust. Moving the MtrCAB pathway from a plasmid construct to the chromosome enabled more control over the quantity of protein expressed, however, no improvement in current was observed. Based on these results, we conclude that the MtrCAB pathway can be successfully expressed in M. atlanticusand requires further optimization for reliable biofilm based ET. Engineered living conductive materials could be used in a range of applications for which traditional conducting polymers are not appropriate including improved catalytic coatings for microbial fuel cell electrodes, self-powered sensors for austere environments, and next-generation living components of bioelectronic devices that interact with the human microbiome.