Do bacteria age or are they immortal?

The term “aging” generally conjures up images of graying hair, slowing pace, and the eventual appearance of wrinkles. Yet, beyond these physical markers, aging is a fundamentally cellular and molecular process, even for organisms like bacteria, which also experience age-related changes.

From humble single-celled organisms to complex mammalian systems, all living organisms experience the impact of passing time, according to a recent report from the American Society for Microbiology.

As they age, cells accumulate damage that impairs function, leading to numerous age-related disorders in humans. But what about bacteria? Can these single-celled entities feel the passage of time?

Bacteria age and binary fission factor

Bacteria, being single-celled organisms, propagate differently from humans. Rather than sexual reproduction, they undergo a process known as binary fission.

In this process, they duplicate their DNA and divide into two, resulting in rapid replication. Interestingly, the fastest-growing bacterium can split in less than 10 minutes.

Historically, it was believed that bacteria, thanks to binary fission’s symmetrical nature, did not age. After all, this process results in a parent and offspring identical in age, leading to a concept dubbed “functional immortality.”

Aging, it was assumed, required an asymmetric division where the parent is older than the offspring.

Aging of bacteria

Contrary to the longstanding belief, evidence emerged in 2005, suggesting that, like us, bacteria do age. The researchers found that Escherichia coli (E. coli) exhibit differences between “old” and “new” (parent and offspring) cells.

These distinctions became evident as scientists watched the cells divide under a microscope, noting that older cells’ growth rate and offspring production decline over time.

Moreover, the senior cells died more frequently than their younger counterparts. Clearly, despite similar appearances, cells underwent divisions that left them functionally asymmetric and susceptible to aging.

Asymmetry to the rescue

So, how does this asymmetry help? It turns out, this type of division is crucial for the population’s overall fitness.

An asymmetric division maintains variance, the variety upon which natural selection acts. More variation typically means a better chance of survival under changing conditions.

One of the key players in this aging process is protein aggregation. This process occurs in bacteria and eukaryotic cells and is associated with age-related diseases in humans, such as Alzheimer’s and Parkinson’s, where harmful protein clumps can lead to cell death.

In bacteria, scientists found a smart way of dealing with this problem. As a feature of asymmetric division, older cells accumulate these proteins segregating age-related damage and keeping their offspring looking “younger” at the molecular level.

Cellular states of stress

Another culprit contributing to aging, both in humans and bacteria, is stress. E. coli cells activate a stress state inside the cell to survive mutations accumulated over their lifetimes.

Some of these mutations, while not lethal, can negatively impact the cell’s fitness by causing a critical protein to lose its function.

In a study analyzing the effects of over 60 different nonlethal loss-of-function mutations in E. coli, researchers found that these mutants increased their metabolic activity to compensate for lost protein function.

Still, this adaptation comes at a cost. These cells grow slower and enter a state similar to purgatory faster than non-mutants, especially in nutrient-poor environments.

The findings suggest an “aging cost” associated with maintaining resistance to stress on a population level. Could understanding bacterial aging lead us to new antibiotic targets? Might this ancient mechanism of aging shed light on certain human diseases perpetuated through cellular stress states?

Complexities of aging

Time and age certainly doesn’t stand still for anyone, humans and bacteria included. But perhaps bacteria’s susceptibility to aging is a blessing in disguise.

These hardy organisms make excellent subjects for studying the nuances of aging, given their rapid growth and the ability to observe numerous generations in a single experiment. After all, understanding the complexity of aging is inherent to unlocking the mysteries of life itself.

The discovery that bacteria are not eternal beings, as once thought, but vulnerable to aging like all living organisms, signifies the interconnectedness of life at every level.

The concept of time, aging, and the decline in function straddle across the biological spectrum, making it possible to draw parallels between the simplest life forms and the most complex ones.

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