Hyperthermophiles are microorganisms that thrive in extremely hot environment from 80 ^oC and upwards. They are the most primitive organisms evolved to survive in the early unhostile earth. The simplest and versatile respiratory electron transport chain of these hyperthermophiles made them suitable candidates for microbial fuel cells (MFC) anode catalysts to generate power at high temperatures. We explored the extracellular electron transfer ability of a hyperthermophilic archaeon called Pyrococccus furiosus (PF). PF is an aquatic anaerobe that grows optimally at 100 ^oC using a wide range of substrates such as carbohydrates and peptides¹. The respiratory chain of PF is simple and unique that it does not require any terminal electron acceptor, rather reduces proton to H₂ through membrane bound enzyme complex called hydrogenase². Their ability to reduce the extracellular oxidants such as insoluble Fe(III) oxide and soluble Fe(III) citrate has been investigated. PF reduced Fe(III) oxide during its growth at 90 ^oC and the PF culture re-suspended in MOPS buffer (pH 7.5) was found to reduce Fe(III) citrate significantly using H₂ as an electron donor. Further, low scan-rate cyclic voltammetry at 90 ^oC using potassium ferricyanide as a mediator showed greater mediated electron transfer by PF compared to the control without PF. The proof of concept study reported here reveals the potential of PF to generate electricity in MFCs at high temperature locations such as in solfataric fields or near hydrothermal vents. Moreover, such studies also help to advance our understanding in the field of biogeochemistry of the early hot environment and exobiology.

References:

1. S. D. Hamilton-Brehm, G. J. Schut and M. W. W. Adams (2005) J Bacteriol., 187(21): 7492–7499
2. S Mukund and M. W. W. Adams (1991) J. Biol. Chem., 266(22), 14208-14216.