Transposon stability and a role for conjugational transfer in adaptive mutability
1Department of Biology, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139, USA.
Summary
Escherichia coli undergoing nonlethal selection show high rates of transposon loss, particularly when linked to lac alleles. This loss, often precise, can be a marker for conjugal DNA transfer events in hypermutable bacteria.
Area of Science:
- Microbiology
- Molecular Biology
- Genetics
Background:
- Prolonged nonlethal selection in Escherichia coli can lead to genetic alterations.
- The transposon Tn10 and the lacI33 allele are often studied in conjunction on episomes.
- Tetracycline sensitivity can arise from specific genetic events.
Purpose of the Study:
- To investigate the frequency and mechanisms of transposon loss in Lac(+) revertants of Escherichia coli.
- To determine the role of conjugal DNA transfer in transposon instability.
- To identify potential markers for hypermutability during nonlethal selection.
Main Methods:
- Culturing Escherichia coli with linked Tn10 and lacI33 on an F'128 episome under nonlethal selection.
- Analyzing Lac(+) revertants for tetracycline sensitivity and transposon presence/absence.
- Distinguishing between transposon loss, precise excision, and amplification events.
- Assessing tetracycline sensitivity in Lac(-) colonies resulting from cell transfer.
Main Results:
- Up to 20% of Lac(+) revertants exhibited tetracycline sensitivity, primarily due to Tn10 loss (precise excision) or amplification.
- Nonlethal selection on lactose medium yielded 10% transposon-free revertants, irrespective of conjugal transfer requirements.
- Approximately 5% of Lac(-) unreverted colonies from cell transfer were tetracycline-sensitive, all showing Tn10 loss.
Conclusions:
- High-frequency transposon loss in Escherichia coli under nonlethal selection is linked to conjugal DNA transfer.
- Transposon loss can serve as a marker for conjugal transfer events.
- Conjugal DNA transfer may be a significant factor in the mutability observed during nonlethal selection, identifying hypermutable bacterial subsets.
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