Molecular cloning and characterization of insecticidal crystal protein genes of Bacillus thuringiensis subsp. morrisoni strain PG14

Abstract

Bacillus thuringiensis subsp. morrisoni strain PG14, a gram positive spore forming soil bacteria, produces parasporal insecticidal crystal protein during its sporulation that is highly toxic to mosquito larvae of Aedes aegypti and Culex quinquefasciatus. Its crystal consists of at least 5 major polypeptides of approximately 144, 135, 128, 65-72, and 28 kDa. In this thesis two genes encoding mosquitocidal proteins of PG14 crystal protein were cloned and characterised. The 128 kDa protein product of one gene was highly toxic to Ac.aegypti larvae but slightly toxic to Cx.quinquefasciatus larvae, whereas the minor protein Products of 58,55, and 45 kDa of another gene (s) were slightly toxic to both species of mosquito larvae. The presence of the 128 kDa protein together with the 58, 55, and 45 kDa protein exhibited the synergistic effect in the toxicity agains t Cx. quinquefasciatus Larvae. These results were similar to those found in B. thuringiensis subsp. israelensis (Bti.) the other serotype strain that is found to be highly toxic to mosquito larvae. The 128 kDa and 58 kDa protein genes of both strains were homologous and the protein products of both strains were immunologically related. The 128 kDa protein of PG14 were also synergize with 58 kDa protein of Bti inthe mosquitocidal activity. The presence of homologous genes which are normally on the large plasmid and the synergistic ability of the gene products suggested that the plasmids might be transmissible between Bacillus strains.