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Small Things Considered: If It Walks Like DNA, and Talks Like DNA…

Conjugative plasmids and transposons have been found guilty of spreading antibiotic resistance genes from pathogen to pathogen. But how do they get past the bacterial defenses against incoming foreign DNA? Most bacteria have some sort of restriction-modification system to take care of just such molecular invaders. With such a system, they modify their own chromosomal DNA by adding methyl groups to specific residues within a short recognition sequence which is different for different enzymes. Incoming DNA that doesn’t have those particular sites methylated is “restricted,” i.e., cleaved, by the restriction endonuclease. This is end of game for an incoming phage or other mobile element that had replicated in a different strain or species.

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Comments (1)

  1. Thank you for you post on conjugative transposons! Conjugative transposons are certainly fascinating driving forces of microbial evolution. However, I think that too often the public is bombarded with information about how microbes, especially those containing antibiotic resistant traits, are evolving to harm us rather than help us, when in reality, trillions of bacteria on and within us are working to keep us alive. One example of this specifically is the gut bacteria that help us degrade the complex carbohydrates we consume. Right now, I am looking at how new polysaccharides in our diet are challenging our gut bacteria to evolve and degrade these new substrates. In fact, many carbohydrate utilization loci within the genomes of these bacteria are located on conjugative transposons and seem to have acquired their polysaccharide utilization loci via lateral gene transfer.

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