RESUMO
Growth patterns of trichome and contaminative bacteria in Spirulina sp. liquid culture were observed, and it was found that the number of neutral and alkalophilic bacteria was always 105～106 times of that of Spirulina sp. trichome. It would be very difficult to get real pure Spirulina sp. strain by classical methods of dilution plate, capillary and single trichome selecting methods. A great deal of contaminative bacteria was washed out by two pretreatment processes. Low speed centrifugation was designed to wash the strains which usually deposit at bottom, and filtration method was designed to treat the strains usually floating at surface. Sandwich plate and dilution plate were designed for the purification of the mobile strains and non-mobile strains, respectively. A lot of strains were purified by the above processes and pure single trichome formed pure colonies on plates.