Endospore dipicolinic acid detection during Bacillus thuringiensis culture

Aims: The aim of this work was to detect Bacillus thuringiensis endospore production during fermentation under conditions hindering endospore detection, i.e. in a complex undefined industrial medium with a high content of solids in suspension. Methods and Results: Bacterial endospore production was measured using the photoluminescence of dipicolinate (DPA) with Tb³⁺. The high temperature and pressure of a conventional autoclave was used to release DPA from the endospores. The endospore was obtained from B. thuringiensis var. kurstaki HD‐73 fermentations in industrial‐type media with 25·1 and 54·1 g l^?1 glucose, 4·4 and 35·3 g l^?1 soybean meal, 5·8 g l^?1 yeast extract, 9·2 g l^?1 corn steep solids and mineral salts. Conclusions: In this study, we successfully determined the DPA concentrations during the culture of B. thuringiensis in high‐concentration soybean meal media. A good correlation was found between microscope endospore counting and DPA measurements in the cultures. Significance and Impact of the Study: Because of synergy between Cry protein and endospore in B. thuringiensis bioinsecticides formulation, it is important to be able to determine endospore development during B. thuringiensis industrial‐type fermentation, in order to ascertain the beginning of sporulation.