Identification of two expressed flagellin genes in the insect pathogen Bacillus thuringiensis subsp. alesti

Flagellin from Bacillus thuringiensis subspecies alesti strain Bt75 was isolated both from the culture medium and from flagella. Two protein forms with molecular masses close to 32 kDa were obtained from flagella; one form was identical to the flagellin purified from the culture medium. The N-terminal amino acid sequences were identical for both forms. Two genes coding for flagellin have been identified in B. thuringiensis subsp. alesti. The flaB gene was cloned and sequenced in its entire length. The clone containing the flaA gene was incomplete. Both genes were expressed in the mid-exponential growth phase. The flaB gene was flanked by long (355 bp) direct repeats protruding into the coding region in both the N- and C-terminal parts of the gene. DNA sequences related to the flaB gene were found in most other B. thuringiensis subspecies, and in two of them, subsp. kurstaki and subsp. entomocidus, such sequences were present in multiple copies.