The bacterium Bacillus subtilis is quite adaptable, it moves about in liquids and on agar surfaces by means of flagella and alternatively, it can just stick to an underlying substrate.
The bacteria proliferate most effectively in this stationary state, while motile bacteria reproduce at a noticably lower rate.
In order to sustain and extend the colony, bacteria primarily require sufficient nutrients. Moving slowly means that nutrients are soon used up, but adventurous bacteria that decide to move out fast in search for a microbial Cockaigne may end up feeling lonely.
Which strategy offers the best prospects for the organisms? Should one specialize in growth or migration, or be a generalist and steer a balanced course?
Welcome to the world of theoretical biophysics, which makes theoretical physics look positively rigorous.
Bacillus Subtilis. Photo: Kookaburra / wikipedia.org. Link: Ludwig-Maximilians-Universitaet Muenchen
Ludwig-Maximilians-Universitaet Muenchen theoretical biophysicists in Professor Erwin Frey's group at the Nanosystems Initiative Munich created simulated scenarios, where the bacteria might seeded at the center of a plate containing nutrients. They gradually consume the nutrients available locally and are forced to colonize unpopulated territory.
“We have developed a special mathematical model in which these strategies compete with each other,” says Matthias Reiter, first author of the paper. “And this model enables us to prove that generalists are most successful.”
Experiments have only been performed on homogeneous bacterial cultures consisting of genetically identical cells but the theorists wanted to calculate the behavior of heterogeneous Bacillus subtilis populations. So they assigned a fixed migration rate to each bacterium, inherited by its progeny, and that rate determined the proportion of time the organisms spend in a motile state, as opposed to being engaged in nutrient uptake and proliferation.
Their numerical model derived that, initially, there is intense competition for the limited resources at the edge of the occupied territory. During this phase, individuals that reproduce fast and occupy as much space as possible are at an advantage. But they are soon superseded by colonies of generalists, which devote equal time to migration and proliferation. These gradually spread out, forming sectors as shown in the Figure.
The authors explain this behavior in terms of the invasion speed of so-called Fisher fronts. This speed is maximal in the case of a balance between growth and motility. Initially, colonies that steer a middle course form individual sectors, until they eventually occupy the entire invasion front.
“We intend to test our findings experimentally in cooperation with biologists, in order to compare our theory with experimental work,” Frey said. “It would even be possible to extend the model to more complex ecosystems, since it can, in principle, be transferred to all range-expansion phenomena in which growth and motility are complementary skills.”
Citation: Matthias Reiter, Steffen Rulands, Erwin Frey, 'Range Expansion of Heterogeneous Populations', Phys. Rev. Lett. 112, 148103 (2014) DOI: 10.1103/PhysRevLett.112.148103
- PHYSICAL SCIENCES
- EARTH SCIENCES
- LIFE SCIENCES
- SOCIAL SCIENCES
Subscribe to the newsletter
Stay in touch with the scientific world!
Know Science And Want To Write?
- The Five Stages Of A Dying Theory
- Order Patterned With Chaos - How Climate Is Predicted For Decades - With Exact Forecasts Only For Days
- Should Pregnant Women Be Concerned About BPA?
- Something is wrong in the Arctic
- Is The X(5568) A True Resonance ?
- Determining Prostate Cancer Risk With A DNA Methylation Biomarker
- Neanderthals: Not So Dumb
- "The 30,000 Global Warming Petition Is Easily-Debunked PropagandaNo scientist worth his salt would..."
- "On Feb. 20, 1962, John Glenn became the first American to orbit the Earth. At 3:30 p.m., the Port..."
- "There is a lot of information and a lot of disinformation available to you. You cherry pick the..."
- "That's some serious nonsense right there. Think about what you're saying: Because the world might..."
- "Arsonist will be new Fire ChiefEPA fears 'unprecedented disaster' for environment over Scott Pruitt..."
- NHL's Concussion Protocol, a Closer Look (Part 2)
- Uh-Oh — Smokers Are Drinking the 'Additives Cause the Cancer' Kool-Aid
- A New Way to Prevent HIV Infection
- A Novel Way to Stop HIV
- A Very Cool Way To Treat Carbon Monoxide Poisoning
- It’s Not Brain Surgery, But do You Know What is? Brain Surgery!