This is done to kill off some of the many bacteria in soil that compete with those of the genus Streptomyces. Streptomyces will form spores in the dry soil and will grow on media. Use a marking pen to divide 2 petri plates of isolation medium in half. Immediately spread with flamed loop or glass spreader, being careful not to cross the line drawn to separate the halves. Streptomyces are round, chalky colonies.
Different species are white, greenish brown, gray, pink or other colors.
Using a flamed loop, carefully scrape a well isolated colony of Streptomyces and streak it onto a plate of transfer media. You may divide this plate in half and select 2 or more different colonies, or use another plate. This will be your pure culture. Incubate for 3-5 days at room temp. Make a qualitative observation of the original dilution plates.