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I often find the fungus below growing on my (ostensibly) sterile plates in the 4⁰C room. Presumably it takes a few days to reach this size.

The colony looks puffy and dimpled in the middle, like a chocolate cake. The colony is actually black, but looks grey because of what I assume are hyphae and/or spores on top.

It looks like if I disturb the colony physically spores will be released (I haven't tried this because I don't want to contaminate the whole lab with aggressive spores). I notice that the center of the mass curves upward over time, and after a few more days of growth this colony will probably tear itself apart, leaving a gaping hole in the middle (based observation of similar contaminants on other plates, not pictured).

I suspect this is a very common lab contaminant. It grew to this size in less than 2 weeks, and was at 4C the entire time. I noticed many plates in the same batch/sleeve were contaminated, but each plate had only one colony, so it somehow spreads from plate to plate but not within the plate. What is it?

enter image description here

If anyone has any suggestions for simple but informative, classical microbiological techniques that would help identification (common stains, inexpensive selective media) I would be happy to try them - although it would be hard to justify very involved experiments since this doesn't pertain to my main research (in other words, if this was bacteria, sequencing the 16S would probably be out but a Gram stain is fine - this is very likely not bacteria, but I don't know the equivalents of those methods for fungi). Since identifying species is not really my strong suit, I'd appreciate if you link to a protocol when suggesting methods.

Update: I have found 4 more plates, all LB-Ampicillin, with what I suspect to be the same contaminant. With regard to Alan Boyd's comments, the colony morphology seems to be uniform in several aspects. It is not necessarily flower-shaped as I have claimed, but on the other hand, it never has a halo of satellites (dots) around it either.

Photos of the plates:

  • View from the top (agar side close to the benchtop) - shows round colony morphology and various stages of growth. Bottom left colony shows small dimple as the mass begins to swell. Top right shows cracks (actually tears) appearing as the mass is distorted by growth. Note that there is never two colonies on the same plate. The plates all came from the same sleeve in a cold room storage.
  • View of same colonies from the bottom - note star-shaped inward creases which form as the colonies grow and distort the surface.
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closed as off-topic by WYSIWYG, Chris, AndroidPenguin, The Last Word, AliceD Feb 26 '15 at 9:37

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  • $\begingroup$ Aspergillus niger? $\endgroup$ – Alan Boyd Sep 3 '14 at 17:58
  • $\begingroup$ @AlanBoyd According to the Wikipedia photo, A. niger colonies have a halo of dots around the main disc. In contrast, mine have very tidy edges (even after the middle bursts), and they are flower-like rather than circular. I don't know if this is significant. $\endgroup$ – Superbest Sep 3 '14 at 18:12
  • $\begingroup$ Yes I saw that. However fungal colony morphology is very dependent upon the composition of the agar. But if I was more confident I would have answered, not comented. $\endgroup$ – Alan Boyd Sep 3 '14 at 18:19
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    $\begingroup$ I am far from an expert, but looking at similar pictures around the net I would guess for some Cladosporium species. $\endgroup$ – skymningen Sep 4 '14 at 6:56
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    $\begingroup$ I'm voting to close this question because more details are necessary to answer this question accurately, however, this mould seems like Cladosporium. $\endgroup$ – WYSIWYG Feb 26 '15 at 6:23