Changes in physiological properties as a criterium for detection of plasmid loss in Bacillus thuringiensis

Recent technological improvements have extended the application range of dielectric permittivity biomass measurements to on-line monitoring of physiological changes during bacterial fermentations. In an industrial fermentation of Bacillus thuringiensis, it is important to verify the intactness of bacterial plasmid content in all steps of culture. Changes in certain plasmid resident properties of this bacterium affect the permittivity measurements and could represent the potential signs of change in the plasmid content. In order to study this, the permittivity measurements of cultures of two plasmid-containing (Cry+) and plasmid-free (Cry-) phenotype strains of B. thuringiensis H14 were followed and compared throughout the fermentation. They showed different profiles of permittivity during vegetative growth and sporulation phases which related to the inability of the Cry- phenotype strain to form aggregates and proteinaceous crystals, respectively. Cry- strain grew faster than Cry+ strain, but both of them were able to sporulate. The respiratory quotients of strains were similar during the growth phase but during sporulation phase the Cry- strain had a lower respiratory quotient than the Cry+ strain. Ke