Massive accumulation of purple sulfur bacteria. Thiopedia roseopersicinia, in a spring in Madison, Wisconsin. The bacteria grow near the bottom of the spring pool and float to the top (by virtue of their gas vesicles when disturbed. The green color is from cells of the eukaryotic alga SpirogyraMassive accumulation of purple sulfur bacteria .Thiopedia roseopersicinia,in a spring in Madison,Wisconsin. The bacteria grow near the bottom of the spring pool and float to the top (by virtue of their gas vesicles)when disturbed.The green color is from cells of the eukaryotic alga Spirogyra