A little naked-amoeba-watching, anyone?

Updated: Jun 10, 2019

In the functioning of healthy soil, protozoa play a central role.

Protozoa are single-celled creatures that eat bacteria (for the most part) and poop out whatever nitrogen-rich compounds they don’t use. Without that process, most of the plant nutrients created by bacteria would never become available to plants.

When it comes to protozoa, it’s amoebae that we tend to see most often. A sample of high-quality soil should appear peppered with egg-shaped objects – amoebae that have formed an armored shell in response to disturbance (as in the picture below). The shell is called a ‘test’, the amoeba inside ‘testate.’ Since disturbance is an unfortunate part of sample preparation, the amoebae we see are usually testate.

But not always. When we spot one that’s not, we like to identify it as ‘naked.’

It’s a relatively rare find, but the richer your soil the more likely you’ll find one of those rarer things. Like the other day, when we inspected a recent compost batch: with microbial activity still at high levels, we found the usual testate amoebae all over the place, and before long about a half-dozen naked ones showed up too.

There were a couple like this one, just sitting and not doing much of anything apparent:

There are many species of amoeba, and they’re all very different. Some don’t form tests at all. Some emerge more quickly than others, so they could start showing up once the sample has sat under the microscope for a little while. Some possess a distinct physical structure, others are basically oozing blobs.

Like this one, which was on its way somewhere in a hurry:

A naked amoeba is usually found sitting more-or-less stationary, slowly extending pseudopods (extensions of its body) out toward some other organism or object. An amoeba swallows an object by wrapping a pseudopod around it. In the case of the fast-traveling amoeba, its pseudopods are larger sections of its body stretching out to grab a foothold before the rest of it oozes along behind.

If we don’t find any naked amoebae, it doesn’t mean our soil isn’t healthy. We like to see at least 10,000 amoebae per gram of soil, which is a fraction of the numbers we found in this compost. At those numbers, it’s pretty unlikely you’ll find any naked amoebae.

But keep nurturing your soil microbes, and sooner or later they’ll show up.

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