|My tub of PVA - not looking good...|
|The nastiness in close-up.|
A few minutes later I found an article by Garcia (1988) detailing just how genera of soil Fungi such as Aspergillus and Penicillium could grow in, and thus degrade, PVA when it is the only source of carbon - basically if it's in monoculture as in this case (presumably when the Fungi have no other choice). The research saw the depletion of carbohydrates, protein, and DNA, which was interpreted as an active turnover of those metabolites during degradation. This means these Fungi can metabolise PVA, and not only that, an increase in esterase activity (the enzyme breaking down esters) was seen along with a reduction in viscosity – yes, just like my tub of glue, it got more watery. So, I had suspects - all the circumstantial evidence was there, but was that what happened here?
|Above and below - images of Penicillium under different lighting conditions, showing asexual reproductive structures; this one courtesy of CMI...|
|...and thanks to 'Schimmel' for this one.|
|Aspergillus threads (stained); courtesy of the Australian Society of Cytology Inc.|
|Aspergillus asexual reproductive structure under an electron microscope (Thanks to the Fungal Cell Biology Group)|
A quick trip out to the glue-pot, a sample, my microscope on x400 and what do we get? Well, it’s looking good – many cells/spores and a few elongate/fibrous structures; pretty much exactly as in the rather better pictures above, and many others found on the Web.
|At x400 and unstained, my specimen - threads, cells and maybe squashed reproductive structures.|
I couldn’t find any nice clear examples of those splendid ‘floral’ reproductive structures show in the electron microscope image, but some of the structures seen in my sample do look like rather more battered and squashed versions. So, I’m pretty sure that it’s Fungi such as these that ate my PVA, and I don’t even leave it open when it's not being used; ah well...
Garcia, T.A. (1988). Fungal degradation of polyvinyl acetate. Ecotoxicology and Environmental Safety 16(1): 25-35.