Do bacteria age? Biologists discover the answer follows simple economics

Oct 27, 2011

When a bacterial cell divides into two daughter cells and those two cells divide into four more daughters, then 8, then 16 and so on, the result, biologists have long assumed, is an eternally youthful population of bacteria. Bacteria, in other words, don't age -- at least not in the same way all other organisms do.

But a study conducted by at the University of California, San Diego questions that longstanding paradigm. In a paper published in the Nov. 8 issue of the journal , they conclude that not only do bacteria age, but that their ability to age allows bacteria to improve the evolutionary fitness of their population by diversifying their reproductive investment between older and more youthful daughters. An advance copy of the study appears this week in the journal's early online edition.

"Aging in is often caused by the accumulation of non-genetic damage, such as proteins that become oxidized over time," said Lin Chao, a professor of biology at UC San Diego who headed the study. "So for a single celled organism that has acquired damage that cannot be repaired, which of the two alternatives is better—to split the cellular damage in equal amounts between the two daughters or to give one daughter all of the damage and the other none?"

The UC San Diego biologists' answer—that bacteria appear to give more of the cellular damage to one daughter, the one that has "aged," and less to the other, which the biologists term "rejuvenation"—resulted from a computer analysis Chao and colleagues Camilla Rang and Annie Peng conducted on two experimental studies. Those studies, published in 2005 and 2010, attempted unsuccessfully to resolve the question of whether bacteria aged. While the 2005 study showed evidence of aging in bacteria, the 2010 study, which used a more sophisticated experimental apparatus and acquired more data than the previous one, suggested that they did not age.

"We analyzed the data from both papers with our computer models and discovered that they were really demonstrating the same thing," said Chao. "In a bacterial population, aging and rejuvenation goes on simultaneously, so depending on how you measure it, you can be misled to believe that there is no aging."

In a separate study, the UC San Diego biologists filmed populations of E. coli bacteria dividing over hundreds of generations and confirmed that the sausage-shaped bacteria divided each time into daughter cells that grew elongated at different rates—suggesting that one daughter cell was getting all or most of the from its mother while the other was getting little or none. Click this link to watch the time-lapse film of one bacterium dividing over 10 generations into 1,000 bacteria in a period of five hours and see if you can see any differences.

"We ran computer models and found that giving one daughter more the damage and the other less always wins from an evolutionary perspective," said Chao. "It's analogous to diversifying your portfolio. If you could invest $1 million at 8 percent, would that provide you with more money than splitting the money and investing $500,000 at 6 percent and $500,000 at 10 percent?"

"After one year it makes no difference," he added. "But after two years, splitting the money into the two accounts earns you more and more money because of the compounding effect of the 10 percent. It turns out that bacteria do the same thing. They give one daughter a fresh start, which is the higher interest-bearing account and the other daughter gets more of the damage."

Although E. coli bacteria appear to divide precisely down the middle into two daughter cells, the discovery that the two daughters eventually grow to different lengths suggests that bacteria do not divide as symmetrically as most biologists have come to believe, but that their division is really "asymmetrical" within the cell.

"There must be an active transport system within the bacterial cell that puts the non-genetic damage into one of the ," said Chao. "We think evolution drove this asymmetry. If were symmetrical, there would be no aging. But because you have this asymmetry, one daughter by having more damage has aged, while the other daughter gets a rejuvenated start with less damage."

Explore further: How the signal from light triggers biological action in bacteria

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Cynical1
2.3 / 5 (3) Oct 27, 2011
Proof the evolutionary model makes perfect sense.
antolethron
3 / 5 (2) Oct 27, 2011
The author of this article quoted Lin Chao saying

"Aging in organisms is often caused by the accumulation of non-genetic damage, such as proteins that become oxidized over time"

and then

"If bacteria were symmetrical, there would be no aging."

To me it seems that if the first statement is true, then the second would be false regardless of symmetry.
nanotech_republika_pl
not rated yet Oct 27, 2011
This is amazing stuff. I mean how many people even if they suspected it, explicitly said something like that? So why only 9 votes so far? Do people not vote or are there just 9 people visiting physorg.com?
RealScience
not rated yet Oct 27, 2011
republika - many people don't vote, and even some people who often vote don't bother if the article already has a solid 5-star rating.
tkjtkj
5 / 5 (1) Oct 28, 2011
the interesting thing is that 'damage' here is ill-defined: as evolution involves 'fitness for a varying environment', each instance of a 'daughter-cell with damaged genome' is really merely an 'offering' to possible survival of the species were the environment to change. In that case, 'damage' would mean perhaps 'increased survivability' in some future modified environment .. hardly a detrimental change! Rather, it would be more likely to be the 'key to future survival'.
'Damaged' should be seen as 'opportunity', IMHO. It's the UNdamaged 'daughter' that would be more likely NOT to have abilities to survive adverse conditions, if you get my (genetic) drift. ;))

CHollman82
1.7 / 5 (11) Oct 28, 2011
'damage' here is ill-defined: as evolution involves 'fitness for a varying environment', each instance of a 'daughter-cell with damaged genome' is really merely an 'offering' to possible survival of the species were the environment to change. In that case, 'damage' would mean perhaps 'increased survivability' in some future modified environment .. hardly a detrimental change! Rather, it would be more likely to be the 'key to future survival'.
'Damaged' should be seen as 'opportunity', IMHO. It's the UNdamaged 'daughter' that would be more likely NOT to have abilities to survive adverse conditions, if you get my drift.


This is true, but it's also true that the vast majority of mutations prove to be detrimental during the lifespan of the organism. As a percentage of all mutations it is a very rare occurrence for a mutation to be beneficial, and rarer still for it to be detrimental to begin with but later become beneficial due to a change in the environment.
ean
not rated yet Oct 28, 2011
And what about eukaryotic cells? Mitosis results in two identical daughter cells, perhaps they aren't identical after all? It is assumed that human cell undergoes 52 divisions (Hayflick limit)before senescence. Given each old mother cell divides into two brand new daughter cells, how are divisions counted? This has puzzled me since the early school years.
antialias_physorg
not rated yet Oct 28, 2011
Given each old mother cell divides into two brand new daughter cells, how are divisions counted?

In animal cells this is accomplished via telomeres (repeating base sequences at the end of the DNA strand). With each copy/division the last one doesn't get copied so the telomeres shorten during your lifetime.
When the telomeres become too short the cell automatically performs apoptosis (programmed cell death). This is our mechanism for avoiding accumulation of harmful mutations in cells (and also the reason why we age and die).

There are cells where the telomeres don't shorten or the apoptosis mechanism is disabled. While this may look like a recipe for immortality it just means that the cells accumulate defects and don't perform the purpose they are supposed to (in effect just drawing off nutrients and blocking the space from hosting functional cells). In other words: cancer.
ean
not rated yet Oct 28, 2011

In animal cells this is accomplished via telomeres


Yes, thank you, I know it. And all the new cells (corresponding division count=0) originate from stem cells in adult organisms then. This makes sense.
Eikka
5 / 5 (2) Oct 28, 2011
the interesting thing is that 'damage' here is ill-defined: as evolution involves 'fitness for a varying environment', each instance of a 'daughter-cell with damaged genome'


Except the article didn't speak of damage to the genome, but damage to the structure of the cell.

In essence, it says that when the cell divides, it leaves all the faulty parts in one half, and gives the other half all the good parts. That way one of the copies sacrifices itself to take all off the accumulated structural damage, so the other would have all the working tools to make flawless copies of the genome.

In business terms, this would be like a company splitting into two identical daughter companies, where one gets all the money and the other gets all the debt.
tkjtkj
not rated yet Oct 28, 2011
Re: CHollman82 : " As a percentage of all mutations it is a very rare occurrence for a mutation to be beneficial, and rarer still for it to be detrimental to begin with but later become beneficial due to a change in the environment."


Agreed .. but then, likewise, it's unusual for an environmental change to be beneficial .. 'Adaptation' means 'tuned for the niche' .. change the niche: probably bad news for the nicheee.
And as 'mom nature' cant predict futures any better than we can, she is obliged to present a wide variety of permutations/combinations of genetic capabilities. She cares very little for individuals: her job is, effectively, to worry about the species, not particular individuals. Individuals become important only when they happen to possess a characteristic that makes specie's survival more likely. In geo-time, environs are never stable, either. So: more variability is better.
tkjtkj
not rated yet Oct 28, 2011
the interesting thing is that 'damage' here is ill-defined: as evolution involves 'fitness for a varying environment', each instance of a 'daughter-cell with damaged genome'


Except the article didn't speak of damage to the genome, but damage to the structure of the cell.

In essence, it says that when the cell divides, it leaves all the faulty parts in one half, and gives the other half all the good parts. That way one of the copies sacrifices itself to take all off the accumulated structural damage, so the other would have all the working tools to make flawless copies of the genome.

In business terms, this would be like a company splitting into two identical daughter companies, where one gets all the money and the other gets all the debt.

The only important kind of cell-damage (other than a fatal structural mod) is damage to the DNA/RNA .. for that is where instructions for repair exist. Non-nucleic acid damage isn't inheritable.
CHollman82
1.4 / 5 (10) Oct 28, 2011
Agreed .. but then, likewise, it's unusual for an environmental change to be beneficial .. 'Adaptation' means 'tuned for the niche' .. change the niche: probably bad news for the nicheee.
And as 'mom nature' cant predict futures any better than we can, she is obliged to present a wide variety of permutations/combinations of genetic capabilities. She cares very little for individuals: her job is, effectively, to worry about the species, not particular individuals. Individuals become important only when they happen to possess a characteristic that makes specie's survival more likely. In geo-time, environs are never stable, either. So: more variability is better.


Yes, agreed. I think I was talking to hear myself talk as it seems we are in complete agreement about this.
tkjtkj
not rated yet Oct 28, 2011

Yes, agreed. I think I was talking to hear myself talk as it seems we are in complete agreement about this.


we do agree, yup. .. but if your reasons were thus, I, then am just as guilty ;)
Let's hope some others might have found it interesting ;))

CHollman82
2 / 5 (4) Nov 02, 2011
my roomate's sister makes $85 an hour on the laptop. She has been fired from work for 10 months but last month her paycheck was $8953 just working on the laptop for a few hours. Here's the site NuttyRich.com


Too bad you only make 15 cents a day trying to drive idiots to your scam site...