Eleven days
September 10, 2016 12:28 PM Subscribe
The Evolution of Bacteria on a “MEGA-Plate” Petri Dish - a cinematic approach to visualizing drug resistance
What I really wanted to know was how different all the separate mutations were.
posted by CheeseDigestsAll at 1:34 PM on September 10, 2016
posted by CheeseDigestsAll at 1:34 PM on September 10, 2016
I wish this had been done decades ago so that people arguing for saner antibiotic use would have had an easy-to-understand and irrefutable visual aid to bolster their arguments.
posted by Johnny Wallflower at 1:40 PM on September 10, 2016 [1 favorite]
posted by Johnny Wallflower at 1:40 PM on September 10, 2016 [1 favorite]
In order to achieve high antibiotic resistance, does the final strain lose some of its relative fitness for environments without the antibiotics?
It would be interesting to compare the resistant strain against the original strain in a setting where they had to compete for the same resources.
posted by tss at 2:03 PM on September 10, 2016 [2 favorites]
It would be interesting to compare the resistant strain against the original strain in a setting where they had to compete for the same resources.
posted by tss at 2:03 PM on September 10, 2016 [2 favorites]
What I really wanted to know was how different all the separate mutations were
Probably enough that tensions between them would often boil over into fisticuffs, but in the 11th hour they overcome their differences to advance together in victory against their common enemy. [cough] humans [cough]
posted by CynicalKnight at 2:12 PM on September 10, 2016 [1 favorite]
Probably enough that tensions between them would often boil over into fisticuffs, but in the 11th hour they overcome their differences to advance together in victory against their common enemy. [cough] humans [cough]
posted by CynicalKnight at 2:12 PM on September 10, 2016 [1 favorite]
[cough] humans [cough]
Sounds like you're a little sick there. Need some antibiotics?
That video was pretty amazing to watch.
posted by dazed_one at 2:14 PM on September 10, 2016 [2 favorites]
Sounds like you're a little sick there. Need some antibiotics?
That video was pretty amazing to watch.
posted by dazed_one at 2:14 PM on September 10, 2016 [2 favorites]
That video was pretty amazing to watch.
Wasn't it, though?
posted by a lungful of dragon at 2:28 PM on September 10, 2016
Wasn't it, though?
posted by a lungful of dragon at 2:28 PM on September 10, 2016
That was seriously cool, and quite beautiful in its way.
In order to achieve high antibiotic resistance, does the final strain lose some of its relative fitness for environments without the antibiotics?
Depends on the nature of the mutations but generally yes. There are several common mechanisms through which resistance tends to work, and they all necessarily involve modifying a pathway crucial for the bacteria's growth and survival or (in the case of horizontal transmission of resistance between bacteria by exchanging extra circles of DNA called plasmids) maintaining DNA for and expressing entirely new genes.
Given how finely honed bacterial metabolic pathways tend to be, due to their fast generation time and intense selective pressure, any substantive modification to an enzyme, transmembrane channel, etc is almost bound to come at some energetic cost.
If you took bacteria from the centre band and transferred them to antibiotic-free medium, I'd bet that you'd fairly quickly see reversion mutants, losing their antibiotic resistance and regaining their original fitness for the clean agar. Probably not as quickly -- the revertents' selective advantage would almost certainly be less dramatic than in the original experiment -- but you'd get there.
One of my undergraduate lab projects was growing flu virus in the presence of antibodies against its HA type (haemagglutinin being one of the two main targets for antibodies, the H in "H1N1"), demonstrating that it evolved an escape mutation, then growing those mutants without antibody again and demonstrating that it reverted to the original genotype. A virus isn't a bacterium, but the principle is the same.
posted by metaBugs at 2:30 PM on September 10, 2016 [10 favorites]
In order to achieve high antibiotic resistance, does the final strain lose some of its relative fitness for environments without the antibiotics?
Depends on the nature of the mutations but generally yes. There are several common mechanisms through which resistance tends to work, and they all necessarily involve modifying a pathway crucial for the bacteria's growth and survival or (in the case of horizontal transmission of resistance between bacteria by exchanging extra circles of DNA called plasmids) maintaining DNA for and expressing entirely new genes.
Given how finely honed bacterial metabolic pathways tend to be, due to their fast generation time and intense selective pressure, any substantive modification to an enzyme, transmembrane channel, etc is almost bound to come at some energetic cost.
If you took bacteria from the centre band and transferred them to antibiotic-free medium, I'd bet that you'd fairly quickly see reversion mutants, losing their antibiotic resistance and regaining their original fitness for the clean agar. Probably not as quickly -- the revertents' selective advantage would almost certainly be less dramatic than in the original experiment -- but you'd get there.
One of my undergraduate lab projects was growing flu virus in the presence of antibodies against its HA type (haemagglutinin being one of the two main targets for antibodies, the H in "H1N1"), demonstrating that it evolved an escape mutation, then growing those mutants without antibody again and demonstrating that it reverted to the original genotype. A virus isn't a bacterium, but the principle is the same.
posted by metaBugs at 2:30 PM on September 10, 2016 [10 favorites]
I'd be interested to see if this technique could be used to somehow evolve bacteria that can survive and learn to eat difficult to deal with toxins, like PCBs.
posted by MikeWarot at 3:01 PM on September 10, 2016 [1 favorite]
posted by MikeWarot at 3:01 PM on September 10, 2016 [1 favorite]
I'd be interested to see if this technique could be used to somehow evolve bacteria that can survive and learn to eat difficult to deal with toxins, like PCBs.
Some of those bacteria were found in toxic waste sites, which work like these petri dishes to select for new strains.
posted by a lungful of dragon at 3:22 PM on September 10, 2016
Some of those bacteria were found in toxic waste sites, which work like these petri dishes to select for new strains.
posted by a lungful of dragon at 3:22 PM on September 10, 2016
10x at each step? This is seriously scary.
posted by hexatron at 3:22 PM on September 10, 2016 [2 favorites]
posted by hexatron at 3:22 PM on September 10, 2016 [2 favorites]
Re: PCBs, IANAbioremediation specialist, but I believe Biostimulation is preferred to selecting for what you think might work in a petri dish. Just give rate limiting nutrients to the existing bacteria in the soil (soil microbial diversity is incredible) and let something evolve which will use the contaminant as a carbon source (e.g. benzene, gasoline).
posted by benzenedream at 9:56 PM on September 10, 2016 [2 favorites]
posted by benzenedream at 9:56 PM on September 10, 2016 [2 favorites]
well, this is nightmare fuel.
posted by SecretAgentSockpuppet at 12:24 AM on September 11, 2016 [2 favorites]
posted by SecretAgentSockpuppet at 12:24 AM on September 11, 2016 [2 favorites]
metaBugs wrote:
If you took bacteria from the centre band and transferred them to antibiotic-free medium, I'd bet that you'd fairly quickly see reversion mutants, losing their antibiotic resistance and regaining their original fitness for the clean agar. Probably not as quickly -- the revertents' selective advantage would almost certainly be less dramatic than in the original experiment -- but you'd get there.
Assuming this is true, how would you account for the development of MERSA, which is persistently resistant, or any other of the so-called "superbugs"?
(Oh and by the way: an "eponysterical," I believe is in order.)
posted by Insert Clever Name Here at 10:56 AM on September 11, 2016 [1 favorite]
If you took bacteria from the centre band and transferred them to antibiotic-free medium, I'd bet that you'd fairly quickly see reversion mutants, losing their antibiotic resistance and regaining their original fitness for the clean agar. Probably not as quickly -- the revertents' selective advantage would almost certainly be less dramatic than in the original experiment -- but you'd get there.
Assuming this is true, how would you account for the development of MERSA, which is persistently resistant, or any other of the so-called "superbugs"?
(Oh and by the way: an "eponysterical," I believe is in order.)
posted by Insert Clever Name Here at 10:56 AM on September 11, 2016 [1 favorite]
Assuming this is true, how would you account for the development of MERSA, which is persistently resistant, or any other of the so-called "superbugs"?
The five fundamental forces of the universe are gravitational, electromagnetic, strong nuclear, weak nuclear and spite. Sometimes, the only explanation is spite.
More seriously -- and I want to stress that this is purely speculation, this isn't my area -- my impression is that this is a consequence of the balance between the different selective pressures. If it's true that the cost to bacteria of maintaining resistance is small (this paper (PDF) refers to data suggesting efficiency drops of 1% - 6% for various bacteria carrying drug resistance plasmids), then the selective pressure to lose resistance is quite slight, and you'd expect it to happen fairly slowly. In contrast, in environments where there are lots of antibiotics about -- like hospitals, where infections by multidrug-resistant bacteria seem to be most common -- the selective pressure to keep the resistance is huge. So you'd only need very occasional exposures to antibiotics to rapidly enrich the bacterial population for drug resistance, which would then start to slowly tail off until the next time that population is exposed.
posted by metaBugs at 1:44 PM on September 11, 2016 [1 favorite]
The five fundamental forces of the universe are gravitational, electromagnetic, strong nuclear, weak nuclear and spite. Sometimes, the only explanation is spite.
More seriously -- and I want to stress that this is purely speculation, this isn't my area -- my impression is that this is a consequence of the balance between the different selective pressures. If it's true that the cost to bacteria of maintaining resistance is small (this paper (PDF) refers to data suggesting efficiency drops of 1% - 6% for various bacteria carrying drug resistance plasmids), then the selective pressure to lose resistance is quite slight, and you'd expect it to happen fairly slowly. In contrast, in environments where there are lots of antibiotics about -- like hospitals, where infections by multidrug-resistant bacteria seem to be most common -- the selective pressure to keep the resistance is huge. So you'd only need very occasional exposures to antibiotics to rapidly enrich the bacterial population for drug resistance, which would then start to slowly tail off until the next time that population is exposed.
posted by metaBugs at 1:44 PM on September 11, 2016 [1 favorite]
Assuming a twenty-minute generation time between divisions, eleven days is about 750 generations. In human terms, 750 generations is about 15,000 years. Without any evolutionary/selective pressure on this population, there would have been 2750 =~ 10250 bacteria at the end of the experiment, which is vastly larger than the number of protons in the universe.
I wonder which disturbs me more: the speed with which these organisms respond to their novel environment, or the fact that they're doing so in spite of a 99% or higher fatality rate.
posted by fantabulous timewaster at 6:51 AM on September 12, 2016
I wonder which disturbs me more: the speed with which these organisms respond to their novel environment, or the fact that they're doing so in spite of a 99% or higher fatality rate.
posted by fantabulous timewaster at 6:51 AM on September 12, 2016
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posted by Stark at 1:28 PM on September 10, 2016 [3 favorites]