What does it mean to be an old bacterium?

[icakeov]

I saw this article recently:
https://www.sciencedaily.com/releases/2007/08/070827174320.htm

It says that "A research team has for the first time ever discovered DNA from living bacteria that are more than half a million years old"

Does this mean that this cell hasn't done any divisions since then (and thus avoided mutation), or somehow didn't have any mutations in all this time and might have kept replicating? Or something else?

And if the answer is the former, is this because due to such cold environment, the cell was just "functioning more slowly" and thus had it's "reproduction" process slow down. My impression was that unicellular organisms constantly grow larger and then eventually split.

In other words, what makes a bacterial cell "old"?

I hope I explained the questions well enough, any feedback super appreciated!

 

[BillTre]

I found the article not exactly clear.
Its not clear to me how they determined the age. Perhaps from stratigraphy (determining the age of the layers of the ice in which the bacteria were found).

Some bacteria can actually live reproduce in contact with ice (very slowly).
Many bacteria will just stop and be preserved in the ice, like food in your freezer. Colder is usually better.
Some animals have antifreeze molecules so they don't freeze at usualy freezing temperatures. Some bacteria may have similar molecules.

If the DNA is physically that old, cells should not have been dividing. In each division the old molecular components of the DNA the old DNA should be diluted by 50%. However, from the article it is not entirely clear to if that is what they meant.

My impression was that unicellular organisms constantly grow larger and then eventually split.

Certainly, this usually the case.

In other words, what makes a bacterial cell "old"?

I would think not dividing for a long time would make for an old cell, but not being dead (such as being frozen).
My point of view is that a dividing cell will make two new cells, however it could be argued that new two cells would be half as old as the original cell.

 

[icakeov]

Thanks BillTre

I found the article not exactly clear.
it could be argued that new two cells would be half as old as the original cell.

Would it be ok to also say (from actual physical molecular or atomic presence, rather than their "arrangement") that "half" of each cell's molecules/atoms are as "old" (or "original") as the parent's? From that angle, the "oldness" of a cell would just gradually "dissipate" , eventually there being none left, like a homeopathic experiment gone right.

Also, what confused me about the article (I agree it is super vague, I might try to find the actual research paper) is that they suggested that the bacteria was still "living and functioning". I imagine that it "started" functioning again once they defrosted it, but what I really wonder is whether a cell could develop an ability where it would actually not divide for millennia in "normal" conditions and just keep functioning without going through reproduction (sort of like what neurons do I guess, they seem to live for quite a while before their immanent death comes around).

Thanks again, that was very helpful!

 

[BillTre]

I imagine that it "started" functioning again once they defrosted it

That would be my guess.

I really wonder is whether a cell could develop an ability where it would actually not divide for millennia in "normal" conditions and just keep functioning without going through reproduction

This would surprise me.

 

[jim mcnamara]

but what I really wonder is whether a cell could develop an ability where it would actually not divide for millennia in "normal" conditions and just keep functioning without going through reproduction (sort of like what neurons do I guess, they seem to live for quite a while before their immanent death comes around

Stop and think about it. Under normal conditions all the other bacteria are going gangbusters and our lazy cell does nothing. An ant steps on the one cell. No more cell. No more species. Not dividing and growing would be pretty strongly selected against. Being able to eke out an existence under extreme cold conditions could be an advantage but with extra metabolic cost - the extra biochemistry needed to allow eking out to happen. So if extreme conditions come and go it might be something with an advantage. Periodic ice ages and interglacial (warm) periods are an example.

Milankovitch cycles 101: https://www.universetoday.com/39012/milankovitch-cycle/

 

[256bits]

Bacterial spores are a way of survival in extreme conditions.
https://en.wikipedia.org/wiki/Endospore
The bacteria has to make a choice of whether to reproduce, or make the spores, which would again become a bacterial colony under more favourable conditions. Certainly a method to achieve longevity, and continuation of the DNA.

 

[icakeov]

Thanks 256bits! That is really helpful.
I noticed in the link:

"In endospore formation, the bacterium divides within its cell wall. One side then engulfs the other. "

Does this mean that the bacteria still continues to "reproduce" in some rate throughout millennia, but just never ends up splitting?

(If yes, that is fascinating!)

 

[256bits]

Thanks 256bits! That is really helpful.
I noticed in the link:

"In endospore formation, the bacterium divides within its cell wall. One side then engulfs the other. "

Does this mean that the bacteria still continues to "reproduce" in some rate throughout millennia, but just never ends up splitting?

(If yes, that is fascinating!)

It is my understanding that when spore formation is complete then that is just it - I doubt that a spore itself can make another spore offspring.
You can think of a spore as not really being a bacterium anymore, but a state of the DNA as having the potential to become a bacterium once more.
I am not saying that the spore version is what the research team was working with, or an actual cooled down bacteria with low activity.
Just that it is a way for bacteria to achieve survival in difficult times.

You might want to look up if all bacteria have this capability, and then narrow down to some very broad extent what type the researchers could have been investigating if in fact it was spores that they found. The article could have at least designated a species, or a similar to today's.

 

[icakeov]

Many thanks again 256bits!
By the way, how would you interpret the quote from the wiki page?
It makes it sound like the endospore continues to divide "within", just not split into new endospores.
"In endospore formation, the bacterium divides within its cell wall. One side then engulfs the other. "

 

[BillTre]

It makes it sound like the endospore continues to divide "within", just not split into new endospores.
"In endospore formation, the bacterium divides within its cell wall. One side then engulfs the other. "

See this link for endospore info.
As said above, the endospore is not a something that is going to do a whole lot as a spore.
Its is often a special survival response (like an escape pad leaving a larger vessel which is running out of resources) to bad conditions for the cell.
The cell forms something that can be "woken" up later.
Once awoken, it can resume its normal functions.
In some cases spores might be infections entities. That would be a species specific property.

Ends can be achieved through unusual means in biology.
The end of surviving stringent conditions may be better met by one cell eating the others, because the survivor ends up with more provisions (from the cells it ate).
The other cells being there may be the result of some unrelated previous process.
Hard to tell of course. I'm not a bacteria life cycle specialist.

 

[256bits]

Many thanks again 256bits!
By the way, how would you interpret the quote from the wiki page?
It makes it sound like the endospore continues to divide "within", just not split into new endospores.
"In endospore formation, the bacterium divides within its cell wall. One side then engulfs the other. "

You may be reading too much into the quote you have isolated.
Formation is making something.
The bacterium is making an endospore.
The endospore sits and waits for favourable conditions to become a bacterium again.
End of story.
Billtre previous post for some more good info.

 

[Laroxe]

Yes, I found the article very unclear, I wasn't sure whether they were talking about the recovery of some viable DNA, I'm not sure what they mean by active and living DNA, DNA can only carry out its functions in a living cell. It isn't clear if they recovered all of the DNA or whether the cells became viable. I think despite the cells being frozen or whether they were able to spore or found as spores this is still a huge amount of time. Research like this is plagued by problems of contamination etc and would need several confirmations but it is interesting.