Shocking! Electricity generation from thermophilic microorganisms… Found in marine sediment!

These heat-loving bacteria; called thermophiles, can function in extreme conditions where ‘normal’ bacteria would perish. These extraordinary microorganisms have a range of distinctive abilities: higher activity, greater stability, longer life and utilization of a wide range of fuels. Because of these capabilities there has been an increased effort to explore how these microbes could be used as effective catalysts within microbial fuel cells (MFCs). MFCs facilitate chemical energy from a bio-convertible substrate to be converted directly into energy, this technology is currently an intriguing possible source of sustainable energy. However, the power and current densities that have been generated by these MFCs, have been relatively low. With this problem in mind, Mathis et al. (2007) investigated how MFC technology could be improved and focused on improving the function of the biological catalysts.

Environments such as hydrothermal vents and volcanic hot springs pipes are already known to support thermophilic bacteria life, but marine sediments with temperatures above 50°C, have also been discovered to possess not only mesophilic bacteria but thermophiles too (Madigan et al. 2005).

Within the structure of a MFC, bacteria use an anode as a terminal electron acceptor and use a soluble factor from the environment to act as an electron carrier to mediate the transfer of electrons to the electrode. Mathis et al. (2007) wanted to consider whether higher levels of electricity could be generated without the addition of an electron-carrying shuttle from marine sediment samples operated under thermophilic conditions compared to a those operated in a mesophilic MFC.

Samples were collected 2-30 cm below the sediment surface from Ashley River; Charleston Harbor SC. Sediment fuel cells were constructed and incubated at a designated thermophilic temperature of 60°C and mesophilic temperature of 22°C. For controls, several ‘killed-cell’ sediment fuel cells were constructed and treated with formaldehyde, so as to negate the activities of present sediment bacteria. The results produced; showed that the sediment fuel cells operated at 60°C with no addition of energy sources or electron-carrying mediators, were able to generate electrical currents directly and at nearly a tenfold higher than their counter parts, which had been incubated at 22°C. Mathis et al. (2007) also found the addition of cellulose to be a suitable fueling agent; with the current being sustained.

Community composition was analyzed via the examination of the 16S rRNA genes. It revealed that within the sediment sample incubated at 60°, two types of bacteria dominated: Gram-positive bacteria most related to Thermincola spp. and Gram-negative bacteria related to Deferribacter spp. Of which all cultures strains are know to be thermophilic.   

I found this study particularly intriguing because it extends our knowledge of thermophilic bacterial habitats; Mathis et al. (2007) indicated that thermophilic bacterial communities may be more dynamic and ubiquitous than formerly perceived and that these heat-loving bacteria are not just restricted to extreme thermophilic environments. Generating electricity with cellulose in a MFC under thermophilic conditions was first shown in this study. Which makes it pioneering within the field of research and also gives a promising indication that with the further understanding of the bacterial communities and technological advances of MFC engineering, MFCs could one day been a viable source of sustainable energy.

A review by Kim et al (2008), discussed the advancements, bacterial communities and applications of MFCs. More recently, Fu et al. (2013), have carried out electrochemical and phylogenetic analysis of current generating microorganisms in thermophilic fuel cells.

Mathis, B. J., Marshall, C. W., Milliken, C. E., Makkar, R. S., Creager, S. E. and May, H. D. (2007)

“Electricity generation by thermophilic microorganisms from marine sediment”. 

  Appl. Microbiol. Biotechnol, 78: 147-155.

http://link.springer.com/article/10.1007%2Fs00253-007-1266-4?LI=true

Fu, Q., Kobayashi, H., Kawaguchi, H., Vilcaez, J., Wakayama, T., Maeda, H. and Sato, K. (2013)

“Electrochemical and phylogenetic analyses of current generating microorganisms in a thermophilic microbial fuel cell”. 

 Journal of Bioscience and Bioengineering. 115: 268-271.

Kim, I. S., Chae, K. J., Choi, M. J. and Verstraete, W. (2008)

“Microbial Fuel Cells: Recent Advanced, Bacterial Communities and Application Beyond Electricity Generation”. 

  Environ. Eng. Res, 13: 51-65.

http://www.ceric.net/wonmun3/ksee/2008_13_2_EER354

Madigan, M. T. and Martinoko, J. M. (2005)

“Brock biology of microorganisms”. 

  11st edn. Prenice-Hall, Upper Saddle River, NJ.