Interspecific competition by non-exoelectrogenic Citrobacter freundii An1 boosts bioelectricity generation of exoelectrogenic Shewanella oneidensis MR-1

Abstract

The performance of bioelectrochemical systems (BESs) is significantly influenced by metabolic interactions within a particular microbial community. Although some studies show that interspecific metabolic cooperation benefits BESs performance, the effect of interspecific substrate competition on BESs performance has not yet been discussed. Herein, the impact of interspecific competition is investigated by monitoring the extracellular electron transfer of exoelectrogenic Shewanella oneidensis MR-1 and non-exoelectrogenic Citrobacter freundii An1 alone and simultaneously. The bacterial consortia generate the highest current of 38.4 μA cm^-2, 6 times of that produced by the single strain S. oneidensis MR-1. Though S. oneidensis MR-1 loses out to C. freundii An1 in solution, the competition enhances the metabolic activity of S. oneidensis MR-1 on electrode, which facilitates the biofilm formation and therefore helps S. oneidensis MR-1 to gain an competitive advantage over C. freundii An1. Increased metabolic activity triggers more electrons generation and flavin secretion of S. oneidensis MR-1 which contributes to its excellent exoelectrogenic capacity. The proteomics analysis confirms that the expression of proteins related to lactate metabolism, biofilm formation, and outer membrane c-type cytochromes are significantly upregulated in S. oneidensis MR-1 from bacterial consortia.

Keywords: Bioelectricity; Exoelectrogenic microbes; Extracellular electron transfer; Interspecific substrate competition.