As I might have mentioned already, my favorite protists are the shaggy, shapely, fast-moving ciliates. They have a lot to offer the idle protist-ogler. As a group, they include some of the largest and most ridiculous-looking microbes in the pond. Many are easy to identify without expensive equipment or special techniques. Some, like the noodle-necked Lacrymaria olor, can be recognized at a glance in the light microscope, even at low magnification. Others, like the stately Stentors, may need closer inspection for a species-level classification, but can still be identified by prominent features such as the colour of the cell, or the shape and distribution of various organelles.
Unfortunately, not all ciliates are so easy to tell apart. Some are like the “little brown birds” that plague neophyte birders, and can only be distinguished from one another by very close observation under exacting conditions. And many, I’m sorry to say, are pretty much impossible to identify, even to genus level, without the help of special stains that expose distinctive patterns in the cilia on the surface of the cell body.
The classic technique for exposing these structures is to fix the cells in some noxious and foul-smelling substance and then soak them in solutions containing various compounds of silver. Certain parts of the organism–most conveniently, for our purposes, the ciliary rows and the nuclei–are “argentophilic,” which is to say they stain darkly when exposed to silver. The ability to selectively stain these organelles revolutionized ciliate taxonomy in the second half of the 20th century, and it is still the most important technique available to modern ciliatology.
particular interest in ciliates, I’d never tried it until just a few days ago.
I’ve been slow to get around to this, mainly because it’s hard to do. Even the easiest methods of silver staining call for a cupboard full of powders and solvents, none of which is available at Shopper’s Drug Mart, and some of which must be handled and stored very thoughtfully. To procure the ingredients I had to find suppliers willing to do business with an individual buyer, and in some cases I had to pay special transport fees.
Then, of course, I had to assemble the equipment required to use this stuff safely: graduated cylinders, flasks, funnels, fixing jars, an accurate scale, syringes, latex gloves, etc.
And finally, I had to acquire a bunch of new skills. I haven’t stood at a lab bench since the ninth grade (40 years ago, if you can believe it), so I had to learn how to do simple tasks, like weighing, pouring and mixing. Fortunately, before undertaking any of this, I had the foresight to culture a full-sized biochemist, which was quite expensive and took about 23 years. He is currently living in my basement, and was very helpful at several points.
Here, then, is my first attempt at staining a plain old Paramecium by one of the silver carbonate methods:
Yes, there’s a lot of room for improvement, but, frankly, I’m delighted that it worked at all.
Here’s one more from the same slide, a specimen of a common hymenostome ciliate with the curious name of Glaucoma:
The impregnation could be more uniform, the focus could be sharper and the hot spot from the microscope lamp is downright annoying. However, I can count the kineties and easily see the shape of the macronucleus. That’s a step forward, for me.
The protocol I followed is the one developed by Augustin, Foissner and Adam in 1984 (described in Foissner’s updated guide to basic methods for ciliate taxonomy). I’m told that the original Fernandez-Galiano method gives more consistent results, so I’ll try that next.