Micrograph of a sample from Lake Dagow's anoxic zone at 6 meter
water depth.The reddish color is caused by purple sulfur bacteria.
Some of the phototrophic bacteria contain gas vesicles and form sheets
of several cells. The dark brownish-green, oval-shaped structures are
phototrophic consortia. They are composed of several tightly attached
cells showing a well coordinated behavior.
Phototrophic bacteria are always colored. They are often relatively large and form sheets or net-like structures. Some can form tightly associated consortia of multiple phototrophic cells surrounding a single colorless cell in the center. This symbiotic consortia may represent the majority of phototrophic bacteria present at the oxic-anoxic interface. This type of symbiosis enables non-motile phototrophic bacteria to move towards the light or escape from oxygen.