Changes in the properties of Bacillus thuringiensis after prolonged culture in a rich medium

Four strains of B. thuringiensis, which had been isolated in vegetative form from leaf surfaces, were grown for 500 generations in batch culture in a rich medium. One of the strains, S4g, differed from the parent in the following respects: greater cell width; changed plasmid profile; complete loss of ability to produce d-endotoxins; loss of ability to produce ß-exotoxin and disruption of vip3 gene; radically different fatty acid composition; and altered metabolic activity. Two of the other evolved strains (S1g and S6g) showed differences in fatty acid profiles compared with the parents. Genetic finger-printing showed that there were also mutations in the cry genes of two of the evolved strains (S1g and S2g). The d-endotoxins of strain S6g were significantly less toxic to the larvae of Pieris brassica compared with those of the parent and it also differed in the plasmid content.