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Spotlight – Arash Komeili

We’re going to have an introduction to the works of Dr. Arash Komeili as a starter to today’s topic of prokaryotes. Dr. Komeili earned his bachelor’s in Biology at the Massachusetts Institute of Technology in 1996. He then pursued his Ph.D. from the University of California at San Francisco in 2001 and became an assistant professor at UC Berkeley in 2005.
He has made fascinating findings in the field of prokaryotes, which include his research on magnetosomes in bacteria by specifically studying Magnetotactic Bacteria (MB).

MBs were found in Italy by Salvatore Bellini (1963) and Richard Blakemore (Woods Hole Oceanographic Institution, Woods Hole, Massachusetts) almost 40 years ago (in 1975). Flagellated bacteria from a nearby swamp were found to always swim North in a drop of water on a microscope slide. These bacteria will reverse direction if the local magnetic field is reversed. they were found to be able to block out the stimuli given to them by the environment, be it light or pheromones. They were found to be able to navigate in a straight-line based on the geographical locations of the earth.
Richard Blakemore’s discovery was the finding of magnetosomes inside such bacteria.

Magnetosomes are organelles that have lipid bilayer membranes, embedded with transmembrane proteins andcontain magnetite (iron compound) crystals.  Magentosomes align next to each other forming chains, based on the earth’s magnetic field. They create a magnetic dipole (North and a South pole) that lets them move.

The crystalline magnetic minerals of magnetosomes are made up of three irons and four oxygen groups (Fe3O4 or Fe3S4. This is the exact composition found in regular magnets. MBs use magnetosomes to navigate (magneto-aerotaxis) to the microaerophilic environments in which they thrive, often in the mud, sediment, or specific layer of a water column within various aquatic environments.

Interestingly, magnetosomes are also in the human brains, fish, termites, and pigeons. However, their functions are not exactly known.

One way magnetosomes can stay in place is with the help of filaments that anchor them. Dr. Komeiliand his team were able to obtain microscopic images of these filaments and find out how they make cells behave like motile compasses.

The filament composition of these bacteria made it possible for these and many other MB species to find and maintain the proper membranous shape. These filaments are only distantly related to the ones found in mammalian bodies in that each filament is only designed for a specific task rather than being versatile, as observed in the mammalians’ filaments. Filaments found in MB species are also ATPases, meaning they can break and use ATP to help them bind and perform their designated tasks.

Another interesting finding was that the biomineralization and formation of magnetites didn’t happen in  the observed bacteria until appropriate mineral and low oxygen conditions were met.

Magnetosomes are organelles that aren’t widely known and talked about because of the very few species that have them, so research in this field is quite fascinating as the pieces of information learned are very novel. Other animals, such as pigeons, bats, turtles, salmon, rays and sharks can sense a local magnetic or electrical field (magnetoreception) in order to navigate or find prey (NY Times, 1981). It is unclear on the extent of similarities that may exist between magnetoreception and prokaryotic magneto-taxis.

Reference List:

1. https://www.nytimes.com/1981/06/14/us/tests-of-magnetic-bacteria-illuminate-polarity-s-role.html
2. https://plantandmicrobiology.berkeley.edu/profile/komeili
3. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4104051/
4. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3811606/#:~:text=The%20magnetosome%20chain%20causes%20the,part%20of%20the%20bacterial%20biomass
5. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3811606/#:~:text=The%20magnetosome%20chain%20causes%20the,part%20of%20the%20bacterial%20biomass
6. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5192964/

Images:

1. 1. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3811606/#:~:text=The%20magnetosome%20chain%20causes%20the,part%20of%20the%20bacterial%20biomass
   2. https://www.researchgate.net/figure/Magnetosomes-in-M-gryphiswaldense-A-TEM-micrograph-of-a-wild-type-cell-of-M_fig1_350928181
   3. https://www.sciencedirect.com/science/article/pii/S259015242100009X
   4. https://2014.igem.org/Template:Kyoto/Project/Magnetosome_Formation/content