AimsDecontaminating large, outdoor spaces of Bacillus anthracis spores presents significant problems, particularly in soil. Proof was sought that the addition of germinant chemicals could cause spores of B.anthracis and Bacillus thuringiensis, a commonly used simulant of the threat agent, to convert to the less resistant vegetative form in a microcosm. Methods and ResultsNonsterile plant/soil microcosms were inoculated with spores of B.thuringiensis and two nonpathogenic strains of B.anthracis. A combination of L-alanine (100mmoll(-1)) and inosine (10mmoll(-1)) resulted in a 6 log decrease in spore numbers in both strains of B.anthracis over 2weeks at 22 degrees C; a 3 log decrease in B.anthracis Sterne spore numbers was observed after incubation for 2weeks at 10 degrees C. Negligible germination nor a decrease in viable count occurred in either strain when the concentration of L-alanine was decreased to 5mmoll(-1). Germinated spores of B.thuringiensis were able to persist in vegetative form in the microcosms, whereas those of B.anthracis rapidly disappeared. The pleiotropic regulator PlcR, which B.anthracis lacks, does not contribute to the persistence of B.thuringiensis in vegetative form in soil. ConclusionsThe principle of adding germinants to soil to trigger the conversion of spores to vegetative form has been demonstrated. Bacillus anthracis failed to persist in vegetative form or resporulate in the microcosms after it had been induced to germinate. Significance and Impact of the StudyThe large scale, outdoor decontamination of B.anthracis spores may be facilitated by the application of simple, defined combinations of germinants.