Some algae such as Microcystis, Chrococcus, Osdilatoria, Anabaena etc. cause water blooms in water reservoirs and on death and decay emit bad smell. Water gets contaminated with such things which make the water unfit fordrinking by animals and fishes die in it. An antibiotic chlorellin is extracted from a green alga Chlorella. It is also used in space research. Bacteria are prokaryotic and mostly heterotrophic and play important role in decompositon of dead organic matter thus in cycling of matter in ecosystem.