Dirty sex and microbes....

Stephen M. Marek smmarek at ucdavis.edu
Sat Feb 22 02:21:46 EST 2003

"Perplexed" <comps.etc at ntlworld.com> wrote in message
news:a9d79d15.0302192001.dcd1b4a at posting.google.com...
> naimhling at aol.com (Naimhling) wrote in message
news:<20030124084623.05338.00000080 at mb-ff.aol.com>...
> > Dang! Now that I have your attention....
> >
> > Somebody has to have seen this before; concentric ring patterns seen on
> > isolated circular colonies of common molds such members of Cladosporia,
> > Penicillia, etc?
> >
> > The colonies grow in a fashion that leaves distinct concentric rings
(see the
> > photograph at http://members.aol.com/naimhling/ceilingrings.jpg).  What
are the
> > factors influencing the formation of the rings?
> >
> > C'mon....SOMEBODY knows the answer.  (A bottle of Jameson goes to the
> > response that addresses the question.)
> >
> > Caoimhín

The rings are spores.  Many fungi sporulate in response to light-dark
cycles.  Try growing them in continuous light or dark.  The rings should
become less defined.  However, if the fungal culture has already been
conditioned to light-dark cycles, its circadian rhythm will maintain the
ringed sporulation pattern, for a time.

> I've been working with yeast and moulds from air plates as part of my
> job for a water company. The colonies with concentric rings of
> different colours only seem to grow when there are few competing
> colonies on the same plate and the surrounding air is fairly dry. I
> have also seen small colourless crystals crowning some of these
> colonies.
> I like to think that the reason they appear is purely to keep us poor
> microbiologists from going insane by giving us the occasional pretty
> "jewel" to look at. ;-) (and to make up for the smell!)
> Of course, if anyone knows of a more scientific answer, I'd love to
> know too.;-)

Crystals calcium oxalate are common in fungal cultures.  Some fungi also
produce other secondary metabolites which can precipitate as crytals.

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