CRYSTAL PROTEINS FROM BACILLUS-THURINGIENSIS SEROVAR MEDELLIN

Colombian strains 163-131 and 24-726 of the Bacillus thuringiensis ser ovar. medellin (Btmed), serotype H-30, are very toxic to mosquito larv ea. Strain 24-726 was serologically and biochemically characterized. I t is almost identical to the reference-strain 163-131. The parasporal inclusion of Btmed strain 163-131 was analysed by electron microscopy. The crystal protein matrix was very similar to that observed in B. th uringiensis serovar. israelensis (Bti). Aedes aegypti, Anopheles albim anus and Culex quinquefasciatus larvae were exposed to 500 x the half- lethal concentration (LC(50)) Of Btmed strains, Bti strain 1884 and B. thuringiensis serovar. morrisoni (Btm) strain PG-14. Mortality of Aed es aegypti occurred within approx. 60 min with the four strains, where as C. quinquefasciatus mortality was three times slower with Btmed tha n with strains 1884 and PG14. The onset mortality of Anopheles albiman us starts when other species are already dead. The thermolabilities of the mosquitocidal activities of the crystal proteins were tested by i ncubation of cultures for 20 min at various temperatures. Btmed lost a ll mosquitocidal activity at 73 degrees C, and 1884 and PG-14 at 79 de grees C. Sodium dodecyl sulphate-polyacrylamide gel electrophoresis an alysis of the crystals purified from strain 163-131 shows polypeptides at 100 kDa, multiple bands at 80, 75, 70, 67, and 65 kDa, and two dou blets at 40-41 and 28-30 kDa. Immunodetection with antibodies raised a gainst Bti toxins shows cross-reaction between the 30-kDa and to a les ser extent the 28-kDa polypeptides of Btmed crystals and Cyt A of Bti. A slight response is observed with the 65-kDa Btmed to serum raised a gainst Cry IV D of Bti.