Monday, July 30, 2018

BacterioFiles 349 - Magnet Microbes Make Millivolts

Magnetotactic bacteria with
magnetosome chains visible
From: Edouard Alphandéry
Front. Bioeng. Biotechnol.
DOI: 10.3389/fbioe.2014.00005
This episode: Bacteria that contain tiny magnets can generate an electric current!

Download Episode (6.8 MB, 7.4 minutes)

Show notes:
Microbe of the episode: Mamastrovirus 2

Journal Paper:
Smit B.A., Van Zyl E., Joubert J.J., Meyer W., Prévéral S., Lefèvre C.T., Venter S.N. 2018. Magnetotactic bacteria used to generate electricity based on Faraday’s law of electromagnetic induction. Lett Appl Microbiol 66:362–367.

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Episode outline:
  • Background: Bacteria surprisingly physics masters sometimes
    • Some making non-metallic nanowires, transfer electrons, can generate electricity
  • Also magnetotactic bacteria
    • Make tiny magnets in cells, help orient according to magnetic field
    • Talked before: ep 269, used magnets to generate heat to kill pathogens
  • But magnetism and electricity also physically linked
    • Rotating wire around magnet can generate electric current
    • And electric current generates magnetic field
  • Can magnetic bacteria have same effect?
  • What’s new: Now, scientists publishing in Letters in Applied Microbiology have tested this out and found that magnetotactic bacteria can generate an electric current!
  • Methods: Used species Magnetospirillum magneticum
    • Produces ~15 tiny magnets, magnetosomes, per cell in lab
    • Extracted these magnetosomes, found they didn't clump together in solution
      • Still had membrane around them
  • Tested electric generation with capillary tube
    • Coiled copper wire around to create solenoid, with ends attached to multimeter
    • Flowed cells or purified magnetosomes through it
    • Passed across electromagnet field first to charge
  • Observed hardly any voltage from growth medium alone, ~0.2 mV
    • Cells passing through produced almost 3x more
    • And purified magnetosomes 1.1mV
  • Current produced is alternating; switches direction regularly
    • Why? Could be because of pump action
    • Peristaltic: roller squishes along flexible tube, then next roller comes along
    • Depending on pump, not very smooth pressure
    • So liquid gets pushed forward, then stops or even flows back a bit
    • Also possible the electromagnet collected particles until clump got dislodged, caused jump
  • Summary: Bacteria that make tiny magnet particles inside their cells can be used to generate electric current by pumping them through a tube with wire coiled around it
  • Applications and implications: Not very much current, hard to imagine a practical application
    • Maybe very low requirement, inaccessible place
    • Where magnetotactic bacteria naturally grow and flow through, coil a wire
    • Probably takes a lot more power to pump through tube than they generate
      • And moving liquid can generate power more directly, like hydroelectric
  • Right now, chemical-derived current from microbial fuel cells more practical
    • But improvements of system could be made
  • What do I think: Distinction between microbe and machine not always very great
    • Even minerals and physical properties are amenable to microbial chemical ingenuity
  • We still have much we can learn

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