Biological Limitations Of Shewanella Oneidensis Mr-1 In Bioelectrochemical Systems

Abstract

Shewanella oneidensis MR-1 is a model microbe for use in bioelectrochemical systems (BESs) for several reasons, including its ability to produce electric current in the presence of oxygen and its use of endogenous electron shuttles for electron transfer. I performed in-depth studies on the growth and physiology of S. oneidensis to gain insight into BES performance with this microbe. In the first study, I analyzed changes in current production when oxygen was added to batch- and continuously-fed BESs with S. oneidensis. These experiments revealed that oxygen is more beneficial under continuously-fed conditions because it allows S. oneidensis to grow and produce flavins at a faster rate, and therefore decreases flavin washout. In the second study I optimized poised electrode potentials, because previous research suggested that electrodes poised at oxidizing potentials may cause a stress response in S. oneidensis. I grew S. oneidensis in continuously-fed BESs with potentiostatically poised electrodes at 5 different redox potentials and concluded that oxidizing electrode potentials do not cause a general stress response, but decrease current production by direct damage of biofilm cells at the electrode surface. In the third study, I compared the transcriptomes of S. oneidensis grown in a wide variety of conditions and used machine learning to discover genes important to anode- and iron-respiration in this organism. This meta-analysis revealed that some putative members of the electron transport chain, including an NADH dehydrogenase and a cytochrome oxidase, were important under anode- or Fe(III)-respiring conditions. Knockouts strains with these genes deleted confirmed their role in the anaerobic electron transport chain of S. oneidensis. Future work is needed to better characterize the efficiency of the anaerobic electron transport chain in S. oneidensis. The overall finding of this work is that S. oneidensis is not appropriate for use in BES applications that require strict anaerobic conditions or quick exchange of medium (e.g., wastewater treatment), because it performs better when mediators and planktonic cells are not washed out of the system