MOSQUITOCIDAL ACTIVITY OF THE CRYIC DELTA-ENDOTOXIN FROM BACILLUS-THURINGIENSIS SUBSP AIZAWAI

The cloned 135-kDa CryIC delta-endotoxin from Bacillus thuringiensis i s a lepidopteran-active toxin, displaying high activity in vivo agains t Spodoptera littoralis and Spodoptera frugiperda larvae and in vitro against the S. frugiperda Sf9 cell line. Here, we report that the CryI C delta-endotoxin cloned from B. thuringiensis subsp, aizawai HD-229 a nd expressed in an acrystalliferous B. thuringiensis strain is also to xic to Aedes aegypti. Anopheles gambiae, and Culex quinquefasciatus mo squito larvae. Furthermore, when solubilized and proteolytically activ ated by insect gut extracts, CryIC is cytotoxic to cell lines derived from the first two of these dipteran insects. This activity was not ob served for two other lepidopteran-active delta-endotoxins, CryIA(a) an d CryIA(c). However, in contrast to the case with a lepidopteran and d ipteran delta-endotoxin cloned from B. thuringiensis subsp, aizawai IC 1 (M. Z. Haider, B. H. Knowles, and D. J. Ellar, Eur. J. Biochem, 156: 531-540, 1986), no differences in the in vitro specificity or processi ng of CryIC were found when it was activated by lepidopteran or dipter an gut extract. The recombinant CryIC delta-endotoxin expressed in Esc herichia coli was also toxic to A. aegypti larvae. By contrast, a seco nd cryIC gene cloned from B. thuringiensis subsp. aizawai 7.29 (V. San chis, D. Lereclus, G, Menou, J, Chaufaux, S, Guo, and M. M. Lecadet, M ol. Microbiol. 3:229-238, 1989) was nontoxic. DNA sequencing showed th at the two genes were identical. However, CryIC from B. thuringiensis subsp. aizawai 7.29 had been cloned with a truncated C terminus, and w hen it was compared with the full-length CryIC delta-endotoxin, it was found to be insoluble under alkaline reducing conditions. These resul ts show that CryIC from B. thuringiensis subsp. aizawai is a dually ac tive delta-endotoxin.