Wednesday, September 23, 2009
Green Ball Mystery Solved
Well, I finally found out what these gelatinous green balls are, the ones my friend Ellen found floating by the thousands in Pyramid Lake a week or so ago (See blog post for 9/14). Here's another photo of one I picked out of the water, just to give some sense of scale.
I went out to Skidmore College today to call on Professor of Biology David Domozych, taking along a small jar of the stuff I'd lifted out of the lake. And he knew at a glance what it was. "Those sure look like Nostoc balls," he said, and he whisked me down the hall to his lab, where we looked at one under the microscope. "No doubt about it," he said as he explained that each gelatinous ball was composed of a colony of numerous filaments of cyanobacteria, contained within a thin membrane. He seemed a good deal interested in our find, explaining that these balls are not all that common, occurring in only about 2% of ponds and other wetlands.
To get a better look, Professor Domozych sliced one of the balls with a razor and smeared some of the contents onto a slide, which he carried off to another microscope that displayed an image on a computer screen. Now I could see the strands of cells, strung like beads on a necklace, the semi-opaque green ones interrupted here and there with clear colorless ones. The green cells contain the chlorophyll that allows this cyanobacteria to photosynthesize, creating nutrients from sunlight. The clear cells, he explained, are "heterocysts," the sites of nitrogen fixation, where atmospheric nitrogen is converted into ammonia. The straight streaks you can see in this photo are the remains of the razor-sliced membrane that enclosed all these filaments.
He then illuminated the slide with ultraviolet light, causing the chlorophyll-laden cells to fluoresce an eerie red. He pointed out that the heterocysts did not react to the light like that. No chlorophyll, no fluorescence. I'm very grateful to Professor Domozych for giving me a copy of these photos to show on my blog. I told him he could keep the samples I fished out of the lake, and he seemed pleased to have them, explaining that his students could cultivate some more. Cyanobacteria is fascinating stuff.
Professor Domozych told me that these Nostoc balls can sometimes grow to the size of baseballs; he had heard about some pond in California, where these large balls sink at night and lie on the bottom, but when the sun rises, they pop up to the surface, causing the water to look like it's full of big bubbles. Another thing I learned about them (I found this out browsing the web) is that some species are good to eat. Apparently, you can buy dried Nostoc balls in Asian markets and use them in stir-fries or soups or as thickeners for other foods.
I have certainly learned some new things today about cyanobacteria. Now I'll have to find out how it tastes. But, oh darn! I gave my Nostoc balls away. Too bad.