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A complete physical map of a Bacillus thuringiensis chromosome
1Biotechnology Centre of Oslo, University of Oslo, Norway.
Journal of Bacteriology
|February 1, 1993
Summary
Bacillus thuringiensis produces biological pesticides using insecticidal toxins, often on plasmids. Chromosomal mapping revealed significant variation among strains, suggesting Bacillus cereus and Bacillus thuringiensis should be reconsidered as distinct species.
Area of Science:
- Microbiology
- Genetics
- Molecular Biology
Background:
- Bacillus thuringiensis is a key source of biological pesticides due to its production of insecticidal toxins.
- Toxin genes in B. thuringiensis are frequently located on extrachromosomal plasmids.
- Understanding the genomic organization of these genes is crucial for optimizing biopesticide development.
Purpose of the Study:
- To construct a physical map of the Bacillus thuringiensis chromosome.
- To investigate the genomic location and variation of insecticidal toxin genes (cryIA-type) across different strains.
- To assess the genetic relatedness between Bacillus thuringiensis and Bacillus cereus.
Main Methods:
- Physical mapping of the B. thuringiensis chromosome using NotI restriction enzyme digestion and fragment alignment.
- DNA fingerprinting of 12 B. thuringiensis strains using NotI patterns.
- Hybridization studies using probes for cryIA-type toxin genes and Tn4430 transposon.
- Assays for hemolytic activity and Bacillus cereus enterotoxin presence.
Main Results:
- A physical map of the B. thuringiensis chromosome was constructed, with a total size of 5.4 Mb.
- Significant variation in NotI DNA fingerprint patterns was observed among the 12 strains.
- The cryIA-type toxin gene exhibited varied localization (chromosomal, extrachromosomal, or both) across strains.
- Hybridization data indicated complex integration patterns of toxin genes and transposons, often differing between chromosomal and extrachromosomal DNA.
- Many strains displayed hemolytic activity and B. cereus enterotoxin, suggesting close genetic ties.
Conclusions:
- Bacillus thuringiensis exhibits substantial genomic variability, particularly concerning the location of insecticidal toxin genes.
- The presence of hemolytic activity and Bacillus cereus enterotoxin in B. thuringiensis strains strongly supports a close genetic relationship.
- The findings challenge the current taxonomic distinction between Bacillus thuringiensis and Bacillus cereus, advocating for their reconsideration as a single species.