I poured some agar plates and tried inoculating them with mushroom spores (I don't think they germinated bc of low humidity), but noticed what looks like mold with crystals on the surface of the agar.

My question is, what are these "dew-like" structures?

Top view

Side view

Location: Near Columbus, Georgia

Incubation conditions: Indoors (room temp), covered


1 Answer 1


I initially figured it was condensation from the agar. But it is not on your lid and you said you suspected humidity was low.

I found this here http://www.gettyimages.ca/detail/photo/mold-penicillium-vermiculatum-growing-on-high-res-stock-photography/128606087. penicillium with water droplets with this caption

Mold, Penicillium vermiculatum, growing on agar. The water droplets on the mold are part of the respiration process of the mold.

Those droplets do look like pure water. And oxidative metabolism does produce water:
CHOH+O2 -> CO2 + H2O. It is interesting that the top of the mold is so hydrophobic that the water forms little balls. Why might that be? If you know, comment please.

Other fungi might put stuff in the exudates that collect atop them. I read that some aspergillum species collect droplets of purple exudate on old colonies but I could not find good images. Here is another penicillium with amber looking exudate. These exudates can contain metabolic products.

penicillium colony with exudate from http://thunderhouse4-yuri.blogspot.com/2015/08/penicillium-citrinum.html

Exudates (or Extrolites): Some fungi can produce exudates as a by-product of their growth, many of which can be collected for commercial use. Mycotoxins are by-products (secondary metabolites) which are potent poisons. Penicillium citrinum produces Citrinin, a nephrotoxic mycotoxin which derives its name from the fungus. It may also produce other extrolites such as tanzowaic acid A, quinolactacins, quinocitrinines, asteric acid and compactin.

If these fungi were spreading out in their natural habitat of rotten stuff, the secreted mycotoxins would be clearing a path for them, wiping out those organisms that dare compete for that rotten stuff.

  • $\begingroup$ thanks Will! The droplets looked a little yellow (not captured well in the pic) to be just water, and I was actually going to take a closer look under a microscope once I finished building my flowhood, but now that I know the droplets are likely to occur again, I'll take a closer look without worrying about contamination! If they are waste products, it makes sense that the mold would excrete them onto a hydrophobic surface to avoid poisoning itself! Fascinating. I will share microscopic photos of the surface structure soon. $\endgroup$
    – Diio
    Nov 8, 2017 at 0:08
  • $\begingroup$ I like that scheme about the hydrophobicity providing a dumping ground for wastes. That would make sense. $\endgroup$
    – Willk
    Nov 8, 2017 at 17:52
  • 1
    $\begingroup$ It makes sense that the surface of the mold is hydrophobic if it needs to release spores in the air to get a good dispersion. Just my adaptive interpretation. $\endgroup$
    – bli
    Nov 16, 2017 at 10:37

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