Monday, January 22, 2018

BacterioFiles 325 - Moisture Mobilizes Mycelium Multiples

Mushroom spore print
This episode: Figuring out how mushrooms launch their spores out using a trick of water surface tension!

Download Episode (6.7 MB, 7.3 minutes)

Show notes:
Microbe of the episode: Carrot torradovirus 1

News item

Video of artificial "spore" launching

Journal Paper:
Liu F, Chavez RL, Patek SN, Pringle A, Feng JJ, Chen C-H. 2017. Asymmetric drop coalescence launches fungal ballistospores with directionality. J R Soc Interface 14:20170083.

Other interesting stories:
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  • Gut interactions between bacteria and salt - also this
  • Bacteria can transform toxic metals into less harmful forms (paper)
  • Microbes generating electricity from swine wastewater

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    Episode outline:

    • Background: Fungi spread by very small spores
      • When not just growing and spreading out
      • Sometimes airborne or waterborne or carried on animal
    • But to promote max spread, have ways to make spores go farther
    • Mushroom hunters make spore prints to help ID mushrooms
      • Put cap on paper and see shape and color of spores released onto paper
      • Much more intricate and spread out than simple shape of gills
    • Because mushrooms actually launch spores out from gills
      • Use trick of surface tension from water droplets accumulated on spores
    • What’s new: Now, scientists publishing in the Journal of the Royal Society Interface have worked out more about how this trick works!
    • Spores launch pretty fast, ~2 mph
      • But too light to go far, just fall out of cap, then picked up by airflow
      • Important though, cos otherwise spores might stick to gills
    • Works this way: spore attached to pedestal (sterigma) on gill
      • Kind of semi-sphere shape
      • Film of water forms on flatter side of spore
        • Condensed from water vapor in the air
        • Mannitol and such secreted to pull water out of air, hygroscopic
      • Droplet called Buller’s drop forms at base of spore, near pedestal
        • Observed by Reginald Buller over 100 years ago
    • When droplet merges with film of water, surface tension causes water to spring forward
      • Away from pedestal
      • Pulls spore along with it
    • But this model doesn’t quite explain the behavior
    • Methods: Calculated model to describe physical behavior of launching
    • Then tested model using artificial “spores” made of Styrofoam
      • Much bigger and easier to see/measure than actual spores
      • Spores too small even for high-speed camera to show launch details
      • Link to movie of launch process
    • Applications and implications: Nanotechnology: propulsion, self-cleaning
    • What do I think: Amazing simple aspect of liquid physics accomplishes task of propulsion
      • Don't need mechanics other than shape
      • And chemistry for producing drops with right properties
      • Very effective and consistent in its accuracy
    • Fungi doing nanotech for a while now


    1. Are there any other fields besides nanotechnology this principle can be applied to?

      1. I thought this was a good question so I looked into it a bit. I think probably using surface tension forces as a means of propulsion wouldn't be very useful on larger scales, though water strider insects in the genus Gerridae do use it to walk on the surface of streams.

        But aside from propulsion, surface tension can definitely be an important force and worth considering in different applications. Here's a good summary:

        Surfactants, chemicals that reduce surface tension, can be pretty valuable and I've seen many research papers investigating microbes that can produce them.

        There are some pretty neat home demonstrations of surface tension properties that can be done, too:

        And it's not quite the same thing, but capillary action (adhesion of liquid to another surface rather than to itself) is used in technologies such as chromatography.

    2. Can mushroom hunters identify a poisonous mushroom from the spore print by the pattern or color they see?

      1. The color is the important thing. As an example, there's a kind of big white delicious mushroom called Parasol Mushroom or Macrolepiota procera, which has a white spore print (so you need to use a brown paper bag or something other than white paper to see it), but otherwise looks very similar to the mushroom Chlorophyllum molybdites which is also common and has a green spore print and is mildly toxic. But there are also similar-looking kinds of Amanita mushrooms, which can be deadly poisonous and also have white spore prints, so it's an important factor but not the only factor.

        More advanced mycologists can also learn a lot about a fungus by the shape of its spores directly, but that requires a microscope and such.