Submitted to: Letters in Applied Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/24/2012
Publication Date: 3/27/2012
Citation: Melnick, R.L., Poleatewich, A., Backman, P., Bailey, B.A. 2012. Detection and expression of enterotoxin genes in plant-associated strains of Bacillus cereus. Letters in Applied Microbiology. 54:468-474. Interpretive Summary: Bacillus cereus is bacteria commonly found associated with plants in nature. This bacterium was studied for its beneficial abilities to reduce plant disease and increase plant growth. However, some bacteria produce toxins that cause human illness raising concern over their application to crops. We studied plant associated B. cereus from crop plants to determine whether these naturally occurring isolates have the genes associated with toxin production. We found that some isolates possessed the genes to produce toxins while other isolates lacked these genes. This information can be used by scientists seeking to develop safe and reliable methods for reducing plant diseases and increasing plant growth.
Technical Abstract: Bacillus cereus is an environmental microbe that commonly inhabits plants and soil. Twenty five plant-associated B. cereus isolates were obtained from apple, cacao, tomato, and potato. The isolates were screened for the presence and expression of enterotoxin B (BcET) components of the nonhemolytic enterotoxin (Nhe) and hemolysin BL (HBL) complexes. Nineteen of the B. cereus strains (76.0%) possessed the genes for enterotoxin production. Seven of the nineteen isolates had positive PCR amplification of all genes screened. All isolates that possessed enterotoxin genes were positive for the genes of the nhe operon. Sequencing of PCR amplicons confirmed the presence of enterotoxin genes in the plant-associated isolates. Endophytic B. cereus isolates were capable of expressing enterotoxin genes whether isolates were grown at 25°C or 37°C or in tryptic soy broth or blood heart infusion broth. Generally, isolates that possessed the genes had mRNA transcripts of the genes, except nheA was not expressed by B. cereus isolates Tc11 and TC12. Overall, commonly isolated plant-associated B. cereus isolates can have the genes for enterotoxin production and express these genes in vitro.