The story about operons and the high interconnectedness of prokaryote genomes
makes me wonder: bacteria kick out the antibiotic-coding gene after a few hoursā¦ but how does it know which gene to kick out?
Does it have a way to tell which genes are more āalienā than others? (Or are we only talking about plasmids here?)
Iāve heard itās hard to genomic manipulate some genomes because the cells keep kicking out new genes
One could speculate there is some sort of mechanism, perhaps epi-genetic, that is able to tell which genes are more alien /ā new than others somehow?
Bacteria have systems such as CRISPR that are specialized in detecting exogenous DNA such as from a potential viral infection.
They also have plasmids that are relatively self-contained genetic packets, which are commonly the site of mutations conferring resistance, and which are often exchanged in the bacterial equivalent of sex.
However, to the best of my knowledge, thereās no specific mechanism for picking out resistance genes from others, beyond simple evolutionary pressures.
The genome is so small and compact that any gene that isnāt āpulling its weightā so to speak will likely be eradicated as it no longer confers a survival advantage, such as when the bacteria find themselves in an environment without antibiotics.
Not to mention that some genes are costly beyond the energy requirements of simply adding more codons, some mechanisms of resistance cause bacteria to build more efflux pumps to chuck out antibiotics, or to use alternate versions of important proteins that arenāt affected by them. Those variants might be strictly worse than the normal susceptible version when antibiotics are absent, and efflux pumps are quite energy intensive.
Thereās no real foresight involved, if something isnāt being actively used for a fitness advantage, itāll end up mercilessly jettisoned .
Yeah I think itās a great question and I donāt know that I have a great answer. Plasmids (small rings of DNA that float around separately) are part of the story. My understanding here is pretty sketchy, but I think plasmids are way more likely to be deleted than the chromosomal DNA, and for some reason antibiotic resistant genes tend to be in plasmids (perhaps because they are shared so frequently through horizontal gene transfer)? So the ādelete within a few hoursā bit is probably overstating the average case of DNA deletion in bacteria. I would be surprised if it āknewā about the function of the gene, although I agree it seems possible that some epigenetic mechanism could explain it. I donāt know of any, though!
So happy to see this post appear! š„
The story about operons and the high interconnectedness of prokaryote genomes makes me wonder: bacteria kick out the antibiotic-coding gene after a few hoursā¦ but how does it know which gene to kick out?
Does it have a way to tell which genes are more āalienā than others? (Or are we only talking about plasmids here?) Iāve heard itās hard to genomic manipulate some genomes because the cells keep kicking out new genes
One could speculate there is some sort of mechanism, perhaps epi-genetic, that is able to tell which genes are more alien /ā new than others somehow?
Iād love to hear your thoughts
Bacteria have systems such as CRISPR that are specialized in detecting exogenous DNA such as from a potential viral infection.
They also have plasmids that are relatively self-contained genetic packets, which are commonly the site of mutations conferring resistance, and which are often exchanged in the bacterial equivalent of sex.
However, to the best of my knowledge, thereās no specific mechanism for picking out resistance genes from others, beyond simple evolutionary pressures.
The genome is so small and compact that any gene that isnāt āpulling its weightā so to speak will likely be eradicated as it no longer confers a survival advantage, such as when the bacteria find themselves in an environment without antibiotics.
Not to mention that some genes are costly beyond the energy requirements of simply adding more codons, some mechanisms of resistance cause bacteria to build more efflux pumps to chuck out antibiotics, or to use alternate versions of important proteins that arenāt affected by them. Those variants might be strictly worse than the normal susceptible version when antibiotics are absent, and efflux pumps are quite energy intensive.
Thereās no real foresight involved, if something isnāt being actively used for a fitness advantage, itāll end up mercilessly jettisoned .
Thanks!!
Yeah I think itās a great question and I donāt know that I have a great answer. Plasmids (small rings of DNA that float around separately) are part of the story. My understanding here is pretty sketchy, but I think plasmids are way more likely to be deleted than the chromosomal DNA, and for some reason antibiotic resistant genes tend to be in plasmids (perhaps because they are shared so frequently through horizontal gene transfer)? So the ādelete within a few hoursā bit is probably overstating the average case of DNA deletion in bacteria. I would be surprised if it āknewā about the function of the gene, although I agree it seems possible that some epigenetic mechanism could explain it. I donāt know of any, though!