CHLORELLA

genus of green algae found either singly or clustered in fresh or salt water and in soil. The alga is spherical and has a cup-shaped chloroplast. It is used often in photosynthetic studies, in mass cultivation experiments, and for purifying sewage effluents. Because Chlorella multiplies rapidly and is rich in proteins and B-complex vitamins (one tablespoon of the dried, lima-bean-tasting powder contains as much food value as one ounce of steak), it has been studied as a potential food product for humans both on Earth and in outer space. Chlorella farms, closed systems that provide humans with food, water, and oxygen, have been established in the United States, Japan, The Netherlands, Germany, and Israel. Chlorella's effectiveness in sewage purification depends on a growth-inhibiting substance (chlorellin) it synthesizes that prevents bacterial growth. Chlorella's reproduction is asexual by nonmotile reproductive cells (autospores).