Natural isolates of Bacillus thuringiensis display genetic and psychrotrophic properties characteristic of Bacillus weihenstephanensis

Aim: To determine the potential of Bacillus thuringiensis, known primarily for its entomopathogenicity, to be a psychrotolerant contaminant of stored products. Methods and Results: We determined the genetic properties and diversity of cold-adapted isolates of B. thuringiensis based on (i) the presence of cspA, a genetic determinant that confers psychrotolerance in Bacillus weihenstephanensis, (ii) 16S rRNA genes, and (iii) pulse-field get electrophoretic (PFGE) genome profiles. We assessed the pathogenic potential of these isolates based on whether they harboured various combinations of known toxigenic-associated 1 determinants (nheA, hblA, cytK). Of 36 nonclonal B. thuringiensis cultured from soil and milk, 21 harboured cspA, and of these, 16 (76%) were psychrotolerant and possessed genetic signatures typical of psychrotrophic Bacillus species. The majority of psychrotolerant isolates contained various combinations of nheA, hblA, and cytK. Conclusion: Our results show that natural isolates of psychrotolerant B. thuringiensis occur in soil and milk, and suggest that psychrotolerance is determined by cspA. Significance and Impact of the study: The presence of cspA in combination with nheA, hblA, and cytK could be of concern if commercial products are contaminated with strains that harbour these determinants.