Microbes never fail to surprise me. Their abilities have amazed me for many years and I have become quite the microbe hunter. On my scientific journey, I have met some really interesting microbes. A few years ago, I came across my strangest and most shocking microbial friend yet, Rhodopseudomonas palustris TIE-1.  When I met TIE-1, they were dressed in pink, photogenic and very metabolically versatile. We became friends quickly.

As our friendship grew, I realized that TIE-1 had many hidden talents. Not only could they use electrons from iron to make rust, they could grow like an ancient iron-eating plant. Using light and these electrons from iron, they would thrive (Bose and Newman, 2011 Molecular Microbiology). What surprised me the most was that they would surround themselves in a blanket of rust. I kept wondering what they did under rust, worrying that it would gradually prevent them from getting electrons from iron, something they needed to survive. 

Nonetheless, whenever TIE-1 moved to a new place with enough light, they bounced back to life. This baffled me and I wanted to investigate further. Because rust can conduct electrons, I wondered if TIE-1 was still accessing electrons when under this rusty veil. To test this idea, I had to ask TIE-1 to use electrons from rust proxies such as electrically-poised electrodes. In essence, I asked TIE-1 to eat electricity! This was an undertaking; so, I asked some other friends in my laboratory at Harvard University to help me.

To all of our surprise, TIE-1 was not only able to use electrons from electricity, they even grew while doing this! They did this better when light was around. We published our interesting findings and revealed this shocking diet to the world (Bose et al., 2014 Nature Communications). I was very curious where the electrons TIE-1 took from electricity went. I was able to excite other people in my new laboratory at Washington University in St. Louis to work with TIE-1. In our recent publication, my lab along with collaborators shows that the electrons from electricity are going to the redox pool inside TIE-1 (Guzman et al., 2019 Nature Communications). Eventually these electrons go to carbon dioxide, which serves as a really low potential electron sink. TIE-1 jokingly said to me, “Can’t believe I had to sink this low to use electricity!”  

TIE-1 is very excited to know that not only can they make rust, they can also use electrons from electricity to reduce carbon dioxide. TIE-1 is indeed a light lover and at their best in the sun. On our ongoing adventure, my laboratory is looking for more microbes like TIE-1. We are developing new tools to study these organisms. We hope that this ability to combine electricity and light to reduce the global greenhouse gas, carbon dioxide, might be used to find sustainable solutions to the energy crisis. Most of all, we are finding microbes just like TIE-1 in soils, lakes, rivers and oceans. Who knew that sinking really low to eat electricity was this common and fun TIE-1!

References:

Bose A, Newman, DK. (2011) Regulation of the phototrophic iron oxidation (pio) genes in Rhodopseudomonas palustris TIE-1 is mediated by the global regulator, FixK. Molecular Microbiology 79(1):63-75.

Bose A, Gardel EJ, Vidoudez C, Parra EA, Girguis PR (2014). Electron uptake by iron oxidizing phototrophic bacteria. Nature Communications. 5, Article number:3391.

Guzman MS, Karthikeyan R, Binkley M, Jones C, Ranaivoarisoa TO, Singh R, Fike DA, Meacham JM, Bose A (2018). Phototrophic extracellular electron transfer is linked to carbon dioxide fixation in the bacterium Rhodopseudomonas palustris. Nature Communications. 10, Article number: 1355