Nav: Home

Bacterial population growth rate linked to how individual cells control their size

March 25, 2019

When family weddings all seem to coincide with one another, the phenomenon happens for a reason. An individual and their first cousins tend to be of a similar age, so their weddings usually happen in a similar time frame. But weddings for extended family members, say second and third cousins, tend to be more spread out. This is because the time between one generation to the next varies, meaning that families become more spread out from generation to generation.

A new study by University of Pennsylvania post-doc Farshid Jafarpour from the Department of Physics & Astronomy, who works in the lab of Andrea Liu, reveals that variations in generation times don't accumulate over multiple generations in single-celled organisms, like bacteria. He proposes a new theory, published in Physical Review Letters, that describes how factors that regulate the size of individual cells influence the growth rate of an entire population.

Unlike animals and plants, bacteria increase the size of their population simply by growing in size and then splitting in half to make two new bacterial cells. By studying bacteria when they are dividing on a regular basis, known as the exponential growth phase, Jafarpour was able to develop a model that mathematically describes this fundamental phase of population growth. "If you want to study the physics of bacterial growth, you really want to remove all the other parts that are not part of the growth phase," he says.

Jafarpour used a combination of math equations, computer simulations, and data from biology experiments that tracked the growth of individual bacteria cells. He was surprised to find that the model predicts that bacteria oscillate between slower and faster bursts of growth, in "synchronized bursts of divisions," instead of the population growing at a constant rate. These population-level oscillations in growth now provides a new, mathematical way for biologists to think about and to study population dynamics.

Previously, biologists knew that the generation time in bacteria populations was directly related to the size of individual cells. If a bacterium grows for too long, for example, its daughter cells are larger, and they must divide earlier to compensate for their size difference. This process, known as cell-size regulation, also cancels out some of the variability in the generation time, which keeps the division times in sync with one another for a much longer period of time than previously expected. It's this individual metric of cell size regulation that also seems to be causing the oscillations in growth rates seen in Jafarpour's model.

"The variability in generation times has two different sources: the variability in growth and the variability in division," Jafarpour explains. "The interesting result is that cell-size regulation is completely cancelling out the variability in division, so the only thing that's left is the variability in the growth of the individual cells. And, because that's smaller, the oscillations last a lot longer than you would expect."

This new model can now be used by biologists to obtain information on the variability of individual growth rates, which are difficult to measure in the lab but are extremely important for studying bacterial evolution. And while this model would need some modifications before it could be used to study other species, Jafarpour believes that helping biologists gain a better understanding of the physics that underlie population growth in bacteria is just one of many ways that physics can support the work done by biologists.

"Biology has become more focused on figuring out the molecular basis of mechanisms since the 1950s with the discovery of the structure of DNA, but now we are reaching a level where we have to go back and do more quantitative studies. Physicists have a long tradition of working with real-world systems, knowing how to apply a lot of the quantitative methods developed in mathematics and also understanding what variables are relevant and what variables aren't," Jafarpour says.
-end-
This research was supported by National Science Foundation Grant DMR-1506625.

University of Pennsylvania

Related Bacteria Articles:

How bacteria fertilize soya
Soya and clover have their very own fertiliser factories in their roots, where bacteria manufacture ammonium, which is crucial for plant growth.
Bacteria might help other bacteria to tolerate antibiotics better
A new paper by the Dynamical Systems Biology lab at UPF shows that the response by bacteria to antibiotics may depend on other species of bacteria they live with, in such a way that some bacteria may make others more tolerant to antibiotics.
Two-faced bacteria
The gut microbiome, which is a collection of numerous beneficial bacteria species, is key to our overall well-being and good health.
Microcensus in bacteria
Bacillus subtilis can determine proportions of different groups within a mixed population.
Right beneath the skin we all have the same bacteria
In the dermis skin layer, the same bacteria are found across age and gender.
Bacteria must be 'stressed out' to divide
Bacterial cell division is controlled by both enzymatic activity and mechanical forces, which work together to control its timing and location, a new study from EPFL finds.
How bees live with bacteria
More than 90 percent of all bee species are not organized in colonies, but fight their way through life alone.
The bacteria building your baby
Australian researchers have laid to rest a longstanding controversy: is the womb sterile?
Hopping bacteria
Scientists have long known that key models of bacterial movement in real-world conditions are flawed.
Bacteria uses viral weapon against other bacteria
Bacterial cells use both a virus -- traditionally thought to be an enemy -- and a prehistoric viral protein to kill other bacteria that competes with it for food according to an international team of researchers who believe this has potential implications for future infectious disease treatment.
More Bacteria News and Bacteria Current Events

Trending Science News

Current Coronavirus (COVID-19) News

Top Science Podcasts

We have hand picked the top science podcasts of 2020.
Now Playing: TED Radio Hour

Making Amends
What makes a true apology? What does it mean to make amends for past mistakes? This hour, TED speakers explore how repairing the wrongs of the past is the first step toward healing for the future. Guests include historian and preservationist Brent Leggs, law professor Martha Minow, librarian Dawn Wacek, and playwright V (formerly Eve Ensler).
Now Playing: Science for the People

#566 Is Your Gut Leaking?
This week we're busting the human gut wide open with Dr. Alessio Fasano from the Center for Celiac Research and Treatment at Massachusetts General Hospital. Join host Anika Hazra for our discussion separating fact from fiction on the controversial topic of leaky gut syndrome. We cover everything from what causes a leaky gut to interpreting the results of a gut microbiome test! Related links: Center for Celiac Research and Treatment website and their YouTube channel
Now Playing: Radiolab

The Flag and the Fury
How do you actually make change in the world? For 126 years, Mississippi has had the Confederate battle flag on their state flag, and they were the last state in the nation where that emblem remained "officially" flying.  A few days ago, that flag came down. A few days before that, it coming down would have seemed impossible. We dive into the story behind this de-flagging: a journey involving a clash of histories, designs, families, and even cheerleading. This show is a collaboration with OSM Audio. Kiese Laymon's memoir Heavy is here. And the Hospitality Flag webpage is here.