This post was contributed by Jacob Lazarus, a postdoctoral researcher at Harvard.
There’s an astounding number of ways to create chromosomal mutations in bacteria, so many that it may be difficult to decide which path to take. A quick and easy way to introduce a mutation in the chromosome is to disrupt expression of a gene with an antibiotic resistance cassette. This leaves a “scar” in the chromosome, sometimes interfering with expression of surrounding genes. However, there are ways to create scarless mutations, ones that don’t leave any undesired scars in the chromosome.