Revised click on Chondromyces crocatus REVISITED
Chondromyces crocatus - the bacterium that wanted to be a fungus!
There are a whole range organisms encompassing many hundreds (thousands?) of species that specialize in growing on animal droppings. The droppings of herbivores are rich in all kinds of nutrients that favour growth of microscopic life forms. These include masses of bacteria and the myriads of microorganisms that consume them as a food source e.g. ciliates, flagellates, amoebae and all kinds of protozoans. As well we find rotifers, nematodes, tardigrades and also larger organisms such as mites, springtails, insects and their larvae. Not least amongst this assemblage are the fungi and hundreds of species of fungi have been recorded from herbivore dung. In mycology courses we routinely incubate herbivore dung to find some 'good stuff ' for lab studies and we are seldom disappointed. The dung (horse and sheep droppings are good - moose if you can get it!) is placed on a wet paper towel in a plastic box and then left to incubate at room temperature. You will find new and interesting fungi every day or so for weeks on end. While a few of these are macroscopic unfortunately most are microscopic and you really need both a dissecting microscope and a regular microscope to take full advantage of the wonderful world of dung fungi.
Many years ago a pretty yellowish 'fungus' grew on some sheep dung I had incubated for a week or so in the lab. Under the dissecting microscope I could see this 'fungus' scattered over the surface of the droppings. I thought it was a fungus because it produced clusters of large yellow spores that looked like conidial clusters on branching support stalks (see photomicrograph below). I was wrong! It turned out the organism was a bacterium called Chondromyces crocatus, a species of the Myxobacteriales (Slime Bacteria).
In Cellular Slime Moulds (Acrasiales) under starvation conditions thousands of individual amoebae aggregate in streams and eventually form fruitbodies that mimic fungi. The same thing happens in the Myxobacteriales. In response to a chemical signal, possibly induced by starvation conditions, hundreds of thousands (millions?) of bacteria stream together and produce a massive (relatively) fruitbody. The large yellow "spores" that form clusters at the tips of the branches are actually packages of bacterial cells and each contains many thousands of bacterial rods. If you look a the "spores" at a higher magnification you can see the rods inside (click here). Each 'rod' is a separate bacterium. The spore packages will be dispersed by wind, water and/or insects in the same way as fungus spores and eventually the outer wall will break down and the individual bacterial rods will be released to begin the cycle again. Bacteria are supposed to be microscopic in size but this one produces fruitbodies that can be seen with a hand lens.
Why does Chondromyces do this? I havent seen an explanation but will hazard a guess.
Dung is a rich environment for microscopic life forms. Populations densities are high and competition is fierce. Its a dog eat dog world and survival is for the quickest and the smartest. If you can build up a population quickly and then find a way to escape from the predators that surround you on all sides then you have a better chance for long term survival. What better way than to mimic a fungus and produce fruitbodies with spore packages in the air and well away from the "madding" crowd below. There are of course many solutions to the problem of survival. If you are a student of fungi think of alternative methods of survival for microorganisms such as bacteria and fungi that live at high population densities in competitive environments or have to survive through adverse conditions for extended periods of time.