Fig. 6. The Percoll gradient will be constructed by layering 95 %, 75 %, 50 % and 25 % Percoll solution from bottom to top in a 50 ml ultracentrifuge tube. The spore suspension will be overlayed onto the gradient and centrifuged. After centrifugation, the supernatant will be removed and the spore pellet will be suspended in sterile water. After two or three times purification on Percoll gradient, the resulting pellet will contain very pure spores.