I think with this methodology you could easily exert evolutionary pressure in favor of small *organisms*. But even in a bacterium, the mass of its DNA is <1% of the total mass. So selecting for genome length seems hard. --Michael On Thu, May 12, 2016 at 2:27 PM, Allan Wechsler <acwacw@gmail.com> wrote:
I did not express myself well, if it wasn't clear that I was proposing explicitly measuring and selecting for genome size. A sketch of the experimental procedure:
Grow the organism in ten culture tanks. (The medium should be fixed at the start of the experiment. I expect different results depending on medium.) Ever so often (twelve hours, maybe?) grab a sample from each tank, and use it to "weigh" the genome by electrophoresis; use this data to identify the culture with the smallest average genome. Dump all the cultures except the best; restart the ten tanks with seeds from the best tank. Repeat thousands of times.
On Thu, May 12, 2016 at 1:58 PM, Tom Knight <tk@ginkgobioworks.com> wrote:
You would need a selection for small genome size to get evolution to work on this. While there is a built-in selection for size in that the doubling time is partially paced by genome replication, it is not a sharp selection. Genome replication is heavily pipelined, with 8 copies of the origin of replication and 1 copy of the terminus in rapidly growing coli cells. Also, the 570 kb genome is lacking in a huge number of genes that would normally be considered essential, such as all of the amino acid synthesis genes, all of the fatty acid synthesis genes, all of the nucleotide synthesis genes etc., so the experiment would have to be carried out in a very rich medium containing all of those compounds. Not impossible, and the good news is that likely no one has tried it. But knockouts of genes typically disable them, but don’t remove them. Coli is stable over hundreds of thousands or millions of replication cycles in continuous culture.
On May 12, 2016, at 1:38 PM, Allan Wechsler <acwacw@gmail.com> wrote:
A very late reply to this interesting thread. I am curious to know whether any biologists have tried letting evolution do this work: that is, breed some well-understood model organism (almost certainly E. coli K12 or something similar) and select for small genome. I think genome size can be easily calculated by electrophoresis. This ought to be easy to mechanize, and with a generation time of 17 minutes I suspect that evolution would start whittling away at the 4.6 Mbp genome pretty quickly. Leave it running for a few months and see how close it can get to this 531 Kbp goal line. I have a sneaking suspicion that it would surprise us.
2016-03-27 13:02 GMT-04:00 Warren D Smith <warren.wds@gmail.com>:
http://www.livescience.com/54165-artificial-bacterium-has-smallest-genome.ht...
531K base pairs.
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