I have a reputation for being long-winded but I'll do my best to be brief ...
I inhabit a fishkeeping forum. Someone complained on the forum that the surfaces of plant leaves and wood in his aquarium were becoming covered with a black coating. He posted photos. The photo of the coating on wood looked like cyanobacteria, but it was the wrong colour. I wondered if it could be filamentous Diatoms, which I'd never seen before, so I asked if he'd send me some to look at. He did - samples of both leaves and wood-scrapings.
The samples were packed without excess water and spent three long and cold days in the postal system. When they arrived I transferred them to a dish each, added water containing macronutrients (NPK) and parked them between the top of an aquarium and its lights to recover. I'll refer to the coating on leaves as the 'leaf sample' ; and the coating on wood as the 'wood sample'.
Crushed between a pair of slides, the 'wood' sample was noticeable darker than the 'leaf' sample. After a while, the 'wood' sample in its dish began producing many gas bubbles, while the 'leaf' sample produced very few.
- Day2BubblesSmaller.jpg (158.98 KiB) Viewed 3953 times
Under a microscope (I have a Celestron Pentaview) both samples consisted mainly of a matt of squirming cyanobacteria together with Diatoms of multiple types. The major difference between the two, in context, was the proliferation of these objects in the wood sample (they are absent from the leaf sample) :
- (x400 magnification)
- PICT0008Smallert.jpg (74.43 KiB) Viewed 3953 times
They have a thick wall, and I fancy there's a mucous coat on the outside. They're all the same - I couldn't find any that looked different in terms of the number of 'cells', or were smaller or bigger. They appear to be non-motile and there's no movement discernible inside them. At first I thought that the prominences at either end were tubes, but now I think they're not. It seems unlikely that they photosynthesise, given the dark aspect and thick walls. They didn't appear to be perturbed when I added a few grains of salt to a sample in a well-slide.
My current 'theory' is that they could be heterocycsts because of the supposed hydrogen (or even akinetes) but I've not seen any that are obviously part of a cyano filament, and I haven't found anything near a match in Google images. Something to do with the wood, then? Or something completely independent of both cyano and wood?
I don't know - I'm at a complete loss!
Does anyone have any ideas as to how I might progress to an ID, or even seen these things before?