Bacillus stearothermophilus contains a plasmid-borne gene for alpha-amylase.

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Abstract
The gene for thermostable .alpha.-amylase from the thermophilic bacterium B. stearothermophilus was cloned and expressed in Escherichia coli. Each .alpha.-amylase-producing colony contained at least a 9.7-kilobase-pair (kb) chimeric plasmid composed of the vector pBR322 and a common 5.4-kb HindIII fragment of DNA. B. stearothermophilus contains 4 plasmids with sizes from 12 to over 108 kb. Restriction endonuclease analysis of these naturally occurring plasmids showed they also contain a 5.4-kb HindIII fragment of DNA. Cloning experiments with the 4 plasmids yielded .alpha.-amylase-producing E. coli that contained the same 9.7-kb chimeric plasmid. Restriction endonuclease analysis and further recombinant DNA experiments identified a 26-kb plasmid that contains the gene for .alpha.-amylase. A spontaneous mutant of B. stearothermophilus unable to produce .alpha.-amylase was missing the 26-kb plasmid but contained a 20-kb plasmid. A 6-kb deletion within the region of the 5.4-kb HindIII fragment yielded the 20-kb plasmid unable to code for .alpha.-amylase. A nick-translated probe for the .alpha.-amylase coding region did not hybridize to either plasmid or total cellular DNA from this mutant strain of B. stearothermophilus. The gene for .alpha.-amylase is located exclusively on a 26-kb plasmid in B. stearothermophilus with no genetic counterpart present on the chromosome.