Sapojnik, M., Department of Life Sciences, Ben-Gurion University of the Negev, P.O. Box 653, Be'er-Sheva 84105, Israel
Zaritsky, A., Department of Life Sciences, Ben-Gurion University of the Negev, P.O. Box 653, Be'er-Sheva 84105, Israel
Boussiba, S., Microalgal Biotechnology Laboratory, Blaustein Institute for Desert Research, Ben-Gurion University at Sede-Boker, Sede-Boker 84990, Israel
Manasherob, R., Department of Life Sciences, Ben-Gurion University of the Negev, P.O. Box 653, Be'er-Sheva 84105, Israel, Department of Genetics, Stanford University School of Medicine, Stanford, CA 94305-5120, United States
Ben-Dov, E., Achva Academic College, MP Shikmim 79800, Israel, National Institute for Biotechnology in the Negev, Ben-Gurion University of the Negev, P.O. Box 653, Be'er-Sheva 84105, Israel

The genes cry1Ac and cry1Ca from Bacillus thuringiensis subsps. kurstaki HD-73 and aizawai 4J4, respectively, encoding δ-endotoxins against lepidopteran larvae were isolated, cloned and expressed in Escherichia coli, with and without cyt1Aa (encoding cytolytic protein) and p20 (accessory protein) from subsp. israelensis. Nine combinations of the genes under control of an early T7, PA1 inducible promoter, produced the encoding proteins. Toxicities were examined against larvae of three major agricultural pests: Pectinophora gossypiella, Helicoverpa armigera and Spodoptera littoralis. The clones expressing cyt1Aa, with or without p20, were not toxic. The clone expressing cry1Ac (pBt-1A) was the most toxic to P. gossypiella (LC50 of 0.27 × 108 cells g-1). Clone pBt-1CA expressing cry1Ca and cry1Ac displayed the highest toxicity (LC50 of 0.12 × 108 cells ml-1) against S. littoralis. Clone pBt-1CARCy expressing all four genes (cry1Ca, cry1Ac, p20, cyt1Aa) in tandem exhibited the highest toxicity to H. armigera (LC50 of 0.16 × 108 cells ml-1). Cyt1Aa failed to raise the toxicity of these Cry toxins against P. gossypiella and S. littoralis but significantly enhanced toxicity against H. armigera. Two additional clones expressing either cry1Ac or cry1Ca under tandem promoters, PA1 and PpsbA (constitutive), displayed significantly higher toxicities (7.5- to 140-fold) than their counterparts with PA1 alone, reducing the LC50 values to below 107 cells ml-1. © 2007 Springer-Verlag.