Bacillus thuringiensis HD-1 Cry- : development of a safe, non-insecticidal simulant for Bacillus anthracis

Abstract

Aims: A representative simulant for spores of Bacillus anthracis is needed for field testing. Bacillus thuringiensis is gaining recognition as a suitable organism. A strain that does not form the insecticidal, parasporal crystals that are characteristic of this species is a more accurate physical representative of B. anthracis spores. We developed noninsecticidal derivatives of two isolates of B. thuringiensis HD-1.

Methods and results: Two plasmid-cured derivatives of B. thuringiensis HD-1, unable to make crystal toxins ('Cry(-) '), were isolated. These isolates and the existing Cry(-) strain, B. thuringiensis Al Hakam, were probed with PCR assays against the known insecticidal genes cry, vip and cyt. Their genomic DNA was sequenced to demonstrate a lack of insecticidal genes. This was confirmed by bioassays against a number of invertebrate species. Real-time PCR assays were developed to identify the B. thuringiensis HD-1 Cry(-) derivatives and an effective differential and selective medium was assessed.

Conclusions: All three Cry(-) isolates are devoid of known insecticidal determinants. The B. thuringiensis HD-1 Cry(-) derivatives can easily be recovered from soil and identified by PCR with some selectivity.

Significance and impact of the study: The B. thuringiensis HD-1 Cry(-) derivatives represent accurate, nongenetically manipulated simulants for B. anthracis with excellent human and environmental safety records.

Keywords: Bacillus anthracis; Bacillus thuringiensis; noninsecticidal; safety; simulant; spore.