Relationship with humans

Not only can cyanobacteria be consumed by aquatic organism, but can be also offered as food for humans too, such as spirulina. Spirulina is provided with rich protein in food, therefore can be used in other circumstances, such as manure or fodder. They can be used in agricultural fields because these bacteria contain special cells called heterocyst, which fix and preserve nitrogen in the fields, and spirulina can also reclaim used soil.

Other than the positive effects of cyanobacteria, there are also the negative effects of it. Some cyanobacteria species contain toxins that harm humans and animals, which can be exposed from drinking or bathing in contaminated water. The toxins affect humans with symptoms such as skin irritation, stomach cramps, vomiting, nausea, diarrhoea, fever, sore throat, headache, muscle and joint pain, blister of the mouth, and liver damage. Instant exposure to cyanobacteria toxins may cause asthma, eye irritation, rashes, and blisters around the face.