Counting Cells

In order to adjust the concentration of zoospores in the inoculum I produce for each species or isolate of Phytophthora that I am working with it is necessary to count the number of zoospores in small samples of the inoculum to estimate the concentration. Currently this is achieved using a haemocytometer:

This is a microscope slide with a very fine grid etched into it and when used with a calibrated cover slip the volume of the liquid sample viewed on one square of the grid is known and thus the concentration of particles counted can be calculated from this. Repeat counts are averaged to decrease the error of the estimate. This is a laborious and eye straining activity especially when there are many samples to be adjusted and a time constraint to adjust the concentrations before spores encyst.

This week I have been trying out a new piece of equipment called a 'countess' being developed by Invitrogen, a biotechnology company, I have it on loan for a week for testing and feedback. Here are some images of me trying it out.

I was counting zoospores which are smaller than 10 microns hence the spike in the graph at that size on the x axis. It looks as though there were a couple of sporangia in the sample too as there are 2 small spikes around 40 microns which is about the size of a sporangium which release zoospores (see time lapse slide show in the right bar of this page to see zoospores being released).