[DIYbio] Re: Can a plasmid contain antibiotic synthesis and resistance genes?

One thing seems to have been forgotten in the discussion: Evolution.

Using externally supplied antibiotics, a selection pressure is constantly applied, selecting for cells with resistance to the antibiotic.
If the antibiotic is internally produced, cells could survive not only by expressing a resistance gene, but also by turning off/losing the resistance gene.
As both antibiotic production and resistance has an energy cost, one would expect cells which do not express the antibiotic to have an advantage over cells doing so and thus be selected for. If the antibiotic producing activity is lost, there is then no selection pressure for the resistance gene, and that might rapidly be lost too.

However, as long as there are enough non-revertant cells expressing the antibiotic, the cells in a population might keep each other in check.

This seems like an interesting topic for modelling/simulation. What could the evolutionary dynamics look like in this situation?
Many cells are expressing an antibiotic, thus maintaining selection pressure for the antibiotic resistance genes. However, any one cell might retain the antibiotic resistance genes while dropping the antibiotic production gene, possibly gaining an advantage. If enough cells do this, the advantage of having the antibiotic resistance genes disappear. In the initial condition, any single cell would thus lose out if it dropped both its antibiotic production and resistance genes. However, the population as a whole would benefit (increase growth) by doing so. Could the population overcome the disadvantage, at the single cell level, of mutations that would confer benefit at the population level?

Thoughts?

Best regards,
JP

kl. 22:33:55 UTC+1 tirsdag 29. januar 2013 skrev Nathan McCorkle følgende:

Such that it would first start expressing resistance, which would
trigger antibiotic production. The cell would be protected from the
antibiotic, and as long as the antibiotic was pumped out (maybe the
resistance is an efflux pump) it would only kill neighboring
non-transformants.

This would eliminate the need for buying antibiotics.

--
-Nathan

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