Cyanobacteria Identification

Cyanobacteria are blue-green bacteria that usually appear spherical in shape. They can often be identified with the naked eye because of their tendency to form symbiotic relationships with different organisms, thus creating larger colonies. When viewed under a microscope, these colonies typically appear as chains of individual cells all linked together.

Significance

• Cyanobacteria are bacteria, typically unicellular, that engage in the process of photosynthesis (conversion of light into energy). Cyanobacteria contain a green pigment known as chlorophyll that allows them to perform photosynthesis. They play an important role in the nitrogen cycle by converting nitrogen into organic forms like ammonia and nitrate. Plants like legumes often develop a symbiotic relationship with cyanobacteria, feeding off the organic compounds created by them. Cyanobacteria can also form symbiotic relationships with fungi, thus creating entirely new organisms known as lichens.

Identification

• Cyanobacteria are also known as “blue-green algae” on account of their blue-green hue, which is apparent when viewed under a microscope. However, cyanobacteria can also be seen with the naked eye because they clump together to form massive colonies. Cyanobacteria colonies are usually found in water, both fresh and salt. Look for a thin, green-blue film (also known as pond scum) floating on the surface of standing water. This pond scum is actually a collection of cyanobacteria colonies dwelling on the water’s surface.

  Cyanobacteria are fairly easy to identify under a microscope. However, there are multiple forms of cyanobacteria, each with distinct characteristics. For example, Coccogoneae are spherical cyanobacteria and Hormogonea are cyanobacteria that contain filaments. When you view cyanobacteria under a microscope, look for strands composed of several individual, spherical cells (similar to a chain). These are collections of several Coccogoneae. Be on the lookout for cells that appear blue-green when the light from a microscope shines through them. This will help you identify cyanobacteria more quickly.

  In addition to links of spherical cells, cyanobacteria also exist in the shape of a spiral (Spirulina) as well as individual, bulbous cells. Cyanobacteria lack flagella, which are thin projections that provide mobility for cells by motoring them through liquids. While not self-mobile, cyanobacteria may still show some movement under a microscope because of their inherent ability to glide over watery surfaces.

Warning

• Sometimes cyanobacteria will lose their chlorophyll and become entirely new cells, known as heterocysts. When this occurs, cyanobacteria lose their blue-green tint as well as their ability to perform photosynthesis. This can make them more difficult to identify under a microscope.