Isobutanol production from an engineered Shewanella oneidensis MR-1

Shewanella oneidensis MR-1 is one of the most well-known metal-reducing bacteria and it has been extensively studied for microbial fuel cell and bioremediation aspects. In this study, we have examined S. oneidensis MR-1 as an isobutanol-producing host by assessing three key factors such as isobutanol synthetic genes, carbon sources, and electron supply systems. Heterologous Ehrlich pathway genes, kivD encoding ketoisovalerate decarboxylase and adh encoding alcohol dehydrogenase, were constructed in S. oneidensis MR-1. Among the composition of carbon sources examined, 2% of N-acetylglucosamine, 1.5% of pyruvate and 2% of lactate were found to be the most optimal nutrients and resulted in 10.3 mg/L of isobutanol production with 48 h of microaerobic incubation. Finally, the effects of metal ions (electron acceptor) and direct electron transfer systems on isobutanol production were investigated, and Fe(2+) ions increased the isobutanol production up to 35%. Interestingly, deletion of mtrA and mtrB, genes responsible for membrane transport systems, did not have significant impact on isobutanol production. Finally, we applied engineered S. oneidensis to a bioelectrical reactor system to investigate the effect of a direct electron supply system on isobutanol production, and it resulted in an increased growth and isobutanol production (up to 19.3 mg/L). This report showed the feasibility of S. oneidensis MR-1 as a genetic host to produce valuable biochemicals and combine an electron-supplying system with biotechnological applications.