Analysis of a Protein Fraction in the Spore Coats of Bacillus thuringiensis

The composition and the properties of a protein fraction isolated from the purified spore coats of Bacillus thuringiensis have been studied. This fraction, obtained by action of mercaptoethanol and urea or guanidine on intact coats, shows a strong similarity with crystal protein, with regard to amino acid composition, electrophoretical behaviour and end group analysis (an N‐terminal phenylalanine and a C‐terminal lysine have been found). Immunological studies indicate a partial homology with parasporal inclusion, but not identity. A similar fraction has also been extracted from the spore coats of an acrystalliferous mutant strain. It is concluded that a crystal‐like protein, highly insoluble in character, is one of the components of the spore coats and might be related to other structural proteins associated with the morphogenesis of the spore.