The plating efficiency of Chlorella: so far, its zero

Several weeks ago it occurred to me that I need to answer some really basic questions on my own in order to become more experienced about Chlorella and how it grows, so the first one I decided to ask is:

How efficiently does Chlorella form colonies?

or, put another way:

If I plate 20 live cells, will I get 20 colonies?

This came up partly form a discussion about whether flying insects play any role in between-pond population dynamics of green algae (specifically Chlorella).  But that is another story, pretty much we just wanted to know if you could find green algae on the surface of insects.  The answer to that so far has been “no” (to be posted), and that begged the question if my laboratory strain of Clorella (a planktonic critter) would form colonies on an agar plate.

Metthod: I pulled a big green glob out of my stock slant and resuspended  in 0.5ml of Alga Gro, counted the cells with the hemocytometer, and then spread 25ul, 50ul and 100ul on 3 different kinds of 6cm plates:

Nutrient Agar – a full bodied media containing all kinds of nutrients.  Typically used to grow non-fastidious bacteria.  Has multiple carbon sources.

Pond Alga Agar – a low calorie media containing Carolina’s  Alga Gro supplement (I *think* this is just inorganic salts, but its proprietary) and water from the pond (Carolina reccommends “spring water”, our pond water has to be close enough).

There is plenty of carbon in that pond water.  Since Chlorella is an autotroph it should need that carbon, which will only encourage contaminating heterotrophs. So, I also made up:

dI H2O Alga Agar – a zero calorie version of the above, made with dI water.  A true autotrophic challenege.

The plating efficiency of Chlorella is zero final figure

As a control, I incubated the dilution tubes with the plates under a grow light (12 hours on, 12 hours off) too.  Glad I did that.


My Chlorella culture isn’t pure, which was obvious when I counted cells.  Whatever the “other” is does form colonies but isn’t an autotroph.

Chlorella does not grow into colonies under these conditions.  I wasn’t confident that they would, considering that they are planktonic critters. It might be worth exploring a few different conditions.  Based on my reading, lowering the % agar might be worth trying (easy to do).  Trying to add different factors is a likely solution but is not easy to do in a teaching lab.

Luckily the plaque assay protocol doesn’t require colony growth, but there are questions for which the technically easiest answer would be a plate count.  Those will have to wait.


About SubOptimist

I am an Associate Professor in the Science Department at Georgia Perimeter College, Clarkston. I teach introductory biology courses at both the majors and non-majors level in addition to microbiology. Previous to that I spent 7 years as a postdoctoral researcher on different viruses. While I don't miss being on the "grant treadmill", I think better when I write and miss writing up data for papers and grants; this blog helps me with that a little. And sometimes my kids' insanely funny and cute antics need to be shared with the world. Any view expressed in this blog is that of me personally and not Georgia Perimeter College or the GPC Clarkston Science Department.
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