Cold-loving bacteria: The effect of temperature on psychrotolerant exoelectrogen Shewanella loihica in microbial fuel cells

Abstract

Microbial fuel cells (MFCs) are battery-like devices that use microorganisms called exoelectrogens to oxidise organic matter and release electrons onto electrodes, producing bioelectricity. The transfer of electrons can occur through direct or indirect extracellular electron transfer. An important, highly variable parameter affecting MFCs is temperature. The effect of temperature on MFC technology has hardly been investigated, and therefore, the applicability of MFCs at different temperatures remains undetermined. Psychrotolerant exoelectrogens (PTEs), able to thrive in cold environments, can be used for low-temperature MFC operation. It is expected that the performance of PTE Shewanella loihica in MFCs will increase as the temperature decreases, by influencing its growth, morphology, and extracellular electron transfer. S. loihica was anaerobically cultured at 5°C, 15°C, and 25°C. MFCs operating with S. loihica were set up at the same temperatures and the output potential was monitored for 30 days. The highest growth rate and cell density was observed at 25°C, followed by 15°C. At 5°C, no growth was perceived. Cells were largest in the exponential and stationary phase, and smallest in the lag and death phase. The highest maximum electrical output was obtained at 25°C. However, 15°C showed the highest long-term average. An extremely low electrical potential was observed at 5°C.It can be concluded that S. loihica may have benefits for broadening the thermal window of operation of MFCs towards lower temperatures.