La Morfología De Los Cuerpos Paraesporales Y Su Relación Con La Actividad Biológica En Cepas Cubanas De Bacillus Thuringiensis

The main characteristic of the bacteria Bacillus thuringiensis is the production of parasporal bodies (proteic crys- tals), which constitutes the active principle of commercial bioinsecticides. Crystal's morphology is one of the most used criteria in the characterization of B. thuringiensis strains. The aim of this work was to study the parasporal bodies' morphology of three native strains of B. thuringiensis (LBT-87, LBT-99 y LBT-111) and to determine if there is a correlation between this element and preferential toxicity previously reported for each strain. The B. thuringiensis samples studied belong to the strains' collection of the Instituto de Investigaciones de Sanidad Vegetal, Havana. Bacterial samples were analyzed by Light and Transmission Electron Microscopy. For Light Microscopy, crystal violet stained frotis from autolysated B. thuringiensis cultures were studied. For Transmission Electron Microscopy, ultrathin sections obtained from Spurr embedded B. thuringiensis pellets were analyzed. Crystal's morphology was in correspondence with the biological activity previously reported for each strain. The strain LBT-87, toxic against the dipter insect D. melanogaster, showed irregular crystals with bar-shaped inclusions. The strain LBT-111, toxic against the lepidopter insect H. virescens, presented bipiramidal and cubic crystals. The strain LBT-99, toxic against the nematode M. incognita, presented a very small crystal attached to the spore.