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contamination in Chlamy culture

Elizabeth Harris chlamy at acpub.duke.edu
Thu Nov 13 12:09:52 EST 1997


Marcel Janssen asked:

>I am trying to maintain a pure chlamy culture, a mt+ wild type strain (CC
>1690 or 21 gr). Very frequently cultures appaer to be infected by a very
>small micro-organism. Its diameter is less than one tenth of the diamater of
>a chlamy cell. The organism is only visible at a magnification of 1000 under
>a phase-contrast microscope. The organism is motile and looks to be greenish
>in the interior.
>
>1) Does anybody have an idea what kind of organism this is? (a small green
>alga, a (photo-autotrophic) bacterium or...)
>2) Wil it harm my culture? Or is the organism just living from algal residues
>without influencing the algae?
>3) How could I get rid of it? the answer of this probably depends on the
>answer of question 1.
>


First, are you sure this is a contaminant rather than just brownian motion
of some cellular debris?  If you streak the culture on a rich medium
(Chlamy medium in agar plus yeast extract, peptone, or tryptone, for
instance), do you see colonies of the contaminant growing?

If so, then there are several ways to eliminate it.  You might start with a
visit to the following web site:

http://www.botany.duke.edu/DCMB/methods/cleanup.htm


Personally, I prefer the method I listed on this page, streaking the
culture at low density on nutrient medium, and teasing the Chlamy cells
away from the contaminant with a fine glass needle.  I use antibiotics for
cleanup only as a last-ditch measure.  If the culture is heavily
contaminated, however, so that a streak on nutrient medium produces mostly
bacteria with very few algal cells, then it helps to enrich for the Chlamy
first by growing on minimal medium.

Will it harm your culture?  That really depends on your purpose in growing
the culture, as well as on the nature of the organism.  While Chlamy cells
can exist happily in mixed culture with many kinds of other creatures,
especially in minimal medium in liquid, maintaining contaminated cultures
is hardly desirable.  I'd strongly recommend keeping axenic cultures in any
case.

Are you maintaining your cultures entirely in liquid, with transfer from
one liquid culture to another?  If so, you might want to start keeping a
stock culture on a rich medium on agar, where any new contaminants arising
will be readily apparent and can be eliminated before being transferred to
your experimental cultures.

Elizabeth Harris
chlamy at acpub.duke.edu






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