(Invited) Exoelectrogenicity of Genetically Engineered Hyperthermophiles

Abstract

A hyperthermophilic archaeon called Pyrococcus furiosus (Pf), is being explored as potential microbial catalyst for use microbial fuel cells (MFCs) [Sekar et al. (2017)]. The two main enzymes membrane bound hydrogenase (MBH) and cytoplasmic soluble hydrogenases (SH) are involved in its oxidative fermentative pathways. In P. furiosus the membrane bound hydrogenase (MBH) uses reducing equivalents from the oxidative fermentative pathway to produce hydrogen, which is believed to be used by soluble hydrogenases (SHI and SHII) for nicotinamide cofactor generation. However, in anaerobic respiratory systems, the oxidative fermentative pathways and the activity of MBH and SH enzyme complexes are not fully understood. In this study, we hypothesize that genetically manipulating the expressions of SH and MBH could influence extracellular electron transfer, which could be characterized by an enhancement in organism’s ability to reduce a metal ion (e.g. soluble ferric citrate or and insoluble ferric oxide). Herein, genetic traceable Pf strain was genetically engineered to produce strains with over-expressed SHI (OESHI), over-expressed MbhJ-N (OEMbhJ-N), knocked-out SHI/SHII (ΔSHI/II) or knocked-out MbhL (ΔMbhL). Soluble ferric citrate and insoluble ferric oxide were used to study the ability of engineered Pf strains to reduce the extracellular oxidants. Experiments revealed that the ΔMbhL strain, produced the highest exo-electrogenic ability among these Pf strains. To the best of our knowledge this is the first report that compares the exoelectrogenic ability of different strains of genetically engineered Pf.