2.5. Scanning electron microscopy
The crystalline inclusions of the most toxic isolates were prepared by centrifugation in discontinuous sucrose gradi-ents (Silva et al., 2004). These preparations were washed
and lyophilized before being deposited on a metallic sup-port. The samples were covered with gold for 180 s, using a sputter coater (EMITECH model K550) and observed in a ZEISS model DSM 962 scanning microscope