Cyanobacteria (“Blue-Green Algae”): Gotta love ‘em, gotta hate ‘em
Adding to reports from several other states, the Minnesota Pollution Control Agency this week announced the death of a dog after swimming in a lake harboring a harmful algal bloom (HAB). This summer you too may have witnessed an increase in greenish mats of cyanobacteria, also known as “blue-green algae,” floating on nearby lakes or ponds. Or if you live near a marine environment, you may have seen them on ocean estuaries or bays. If so, you’ve probably wondered, why is this happening? And what are the health consequences? Before answering these questions, let’s consider exactly what cyanobacteria are, and why we should at least respect, if not love, them.
As their name suggests, cyanobacteria contain a blue pigment (the Greek word for blue is kyanos). And they are bacteria, not algae. Like all prokaryotes, cyanobacteria lack a nucleus. But unlike all other bacteria, their cytoplasm contains chlorophyll, which allows them to obtain their energy through photosynthesis. By way of contrast, algae are eukaryotes—their cells, like ours, contain a nucleus. And the reason that cyanobacteria are sometimes wrongly considered algae is that the cells of algae contain chlorophyll within structures called chloroplasts. In fact, these structures found in algae and plants are thought to have originated from an endosymbiotic relationship whereby cyanobacteria were incorporated in algal and plant cells many eons ago. Thus the name “blue-green algae” is a misnomer, and the HABs caused by cyanobacteria should really be called “harmful cyanobacterial blooms.”
It is the chlorophyll in cyanobacteria that should make us revere them. Chlorophyll collects solar energy which converts carbon dioxide and water to produce glucose and oxygen. This phenomenon, called photosynthesis, is shared with algae and plants. The release of a massive amount of oxygen from cyanobacteria, called the “Great Oxygenation Event,” 2.4 billion years ago made life on Earth habitable for aerobic organisms—like us. Even today it is estimated that about half of the world’s oxygen comes from microscopic phytoplankton, such as cyanobacteria. The rest is produced on land by plants.
So cyanobacteria deserve our respect not only because they are the most ancient life form (3.7 billion year-old fossils of cyanobacteria called stromatolites were recently found in Greenland), but also because without them we wouldn’t be here.
Cyanobacteria are ubiquitous. They can be found in almost every terrestrial and aquatic habitat—oceans, fresh water, damp soil, and bare rocks (even rocks in Antarctica). The aquatic cyanobacteria are known for their extensive and highly visible blooms that can form in both freshwater and marine environments. The blooms have the appearance of blue-green paint. Not only are they unappealing to look at, they can be toxic and frequently lead to the closure of recreational waters.
HABs have been increasing in size and frequency worldwide. Currently, they are a major environmental problem in all 50 states. This mounting problem is fueled in part by human activities. Fertilization of plants can lead to nutrient pollution: in particular fixed nitrogen (nitrates, ammonia, and urea) and phosphorus, with runoffs into streams and lakes. Most blooms occur in warm water, and many experts believe that climate change (global warming) has played a substantial role in the genesis of increased HABs.
HABs are destructive because they use up oxygen in the water and block sunlight from reaching fish and plants which can result in massive fish die-offs. In some cases, HABs produce toxins that can sicken or kill a variety of land animals, including aforementioned pet dogs, as well as marine mammals. Although not all algal blooms are hazardous, it is highly recommended not to drink water from or swim in water that is contaminated by an algal bloom.
Finally, the economic impacts of HABs due to losses in the recreation and tourism industry, as well as financial losses from fish die-offs and the deaths of land animals, are providing heightened awareness and monitoring of this growing problem. The continual worsening of HABs is increasing incentives for development of more effective ways to treat and prevent them. But before we completely throw the baby out with the bathwater, let’s remember the vital role that cyanobacteria have played in evolution and our very existence.