Transcriptional Regulation of Shewanella oneidensis Using Native TMAO-Inducible Promoters in a Plasmid-Free System

Abstract

Shewanella species are well known for their ability to respire a multitude of compounds, including insoluble extracellular metals. Shewanella oneidensis MR-1 has emerged as a model organism for understanding the process of extracellular electron transport (EET), in which cells transfer intracellular electrons to an extracellular terminal electron acceptor. The ability of S. oneidensis MR-1 to perform EET also enables it to respire an electrode, which has led to interest in its use for biotechnological applications. The Mtr pathway, a protein conduit that facilitates electron transfer to the extracellular space, is crucial for EET. An ideal synthetic system utilizing S. oneidensis towards biotechnological applications would allow us to control mtr gene expression to dictate EET activity. Here I discuss a native S. oneidensis pathway that can be used to induce gene expression with trimethylamine N-oxide (TMAO). I demonstrate its use in a strain with a TMAO-inducible promoter driving mtr gene expression. qRT-PCR data indicate that the inducible system increases mtr gene expression when the cells are exposed to TMAO. Additionally, TMAO induction of the synthetic system increased extracellular iron reduction, an indicator of increased EET activity. My work expands the genetic components that can be used to engineer S. oneidensis for use in biotechnological applications.