There are about five billion bacteria on Earth. There are about 40 million bacteria in one gram of soil and about 1 million in one milliliter of fresh water. A total of 472 species of bacteria have been recorded from Bangladesh in Encyclopedia of Flora and Fauna of Bangladesh. Among them, 300 species of Cyanobacteria, 60 species of Proteobacteria, 42 species of Firmicutes and 70 species of Actinobacteria.