Nav: Home

How flow shapes bacterial biofilms

June 06, 2019

Although we tend to think of them as solitary sojourners of the world, bacteria are actually very social organisms. In fact, the vast majority of bacteria live on surfaces by forming "biofilms": three-dimensional communities hosting thousands to millions of bacteria of such bustling activity that scientists describe them as "bacterial cities".

Bacteria form biofilms by attaching to each other on a wide variety of surfaces: the bottom of oceans, lakes or rivers, medical equipment and even internal organs, like the intestine, lungs, and teeth - the latter is the familiar dental plaque, a large source of income for dentists.

In short, biofilms are the preferred lifestyle of bacteria. They grow wide and thick, forming a new, social dynamic among their member microorganisms, while also defending them: biofilms can be notoriously inaccessible to antibiotics, which is why they have drawn a lot of medical research.

But looking at biofilms can also give us clues about broader social dynamics that have shaped the evolution of species across the entire planet, like cooperation, competition etc. And it is such questions that drive the work of Alexandre Persat, director of EPFL's Microbial Mechanics Lab.

"About ninety percent of bacterial life at the surface of Earth is found in the form of biofilms" he says. "Because these structures are so dense, they bring many species in proximity, which makes them interact socially and consequently drives their evolution. The outcome of social interactions such as competition or cooperation thus depends on the spatial arrangement of these cells. But what shapes the architecture and the organization of cells in biofilms, for example to mix or segregate, is still unclear."

In a new study, Tamara Rossy, a PhD student in Persat's group, expands our view of biofilms to look at how physical cues affect their development - more specifically, how they are affected by flow of the surrounding fluid. "Whether in oceans, lung infections skin, gut microbiota - the physics of fluids are ubiquitous to biofilms," says Rossy. "We wanted to study how flow changes their spatial organization."

To do this, Rossy had to first create a model biofilm that could be studied under controllable flow conditions. She chose two different clones of the bacterium Caulobacter crescentus, which is commonly found in freshwater lakes and streams, and undergoes a "stalked" cell stage that allows it to anchor on surfaces, colonize them, and form biofilms. Rossy grew the bacteria in microfluidic chips within which she could carefully control minute amounts of liquid flowing through channels just half a millimeter wide.

Rossy imaged the formation of biofilms at the level of single bacteria to monitor the effects of each flow rate on the bacterial colonies. The results showed dramatic differences in architecture between different flows: in weak flows, biofilms were very dense. In stronger flows, bacteria grew in sparse, cluster-like biofilms.

To understand this process, Rossy built a physical model that is reminiscent of the transport of molecules in fluidic systems. Using it, she found that stronger flows can dramatically impair the ability of bacteria to swim towards a surface and colonize it, resulting in sparse colonies.

But some results were also counter-intuitive. "High flow rates lower the probability of swimming bacteria to invade existing colonies," says Rossy. "In order to grow in such high flows, single cells rely on immediate attachment of daughter cells close to their mother cells."

Stronger flows also segregated the two populations, with potentially significant effects on the overall social dynamics between biofilm-dwelling bacteria. "Low and high flow really matter to the arrangement and structure of the biofilm," says Persat. "This shows that flow and, more generally, the physical environment of biofilms can affect the evolutionary history of a bacterial species; this is true at least between different bacterial clones like the ones we used, but it is very likely to apply across different bacterial species."

"Biofilms are a really fascinating and important facet of microbial life," he concludes. "We are only now appreciating how physical principles guide their architecture and how this feeds back into bacterial physiology and evolution. But we have only here scratched the surface -- there is still so much to learn."

Ecole Polytechnique Fédérale de Lausanne

Related Bacteria Articles:

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.
Drug diversity in bacteria
Bacteria produce a cocktail of various bioactive natural products in order to survive in hostile environments with competing (micro)organisms.
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

Teaching For Better Humans 2.0
More than test scores or good grades–what do kids need for the future? This hour, TED speakers explore how to help children grow into better humans, both during and after this time of crisis. Guests include educators Richard Culatta and Liz Kleinrock, psychologist Thomas Curran, and writer Jacqueline Woodson.
Now Playing: Science for the People

#556 The Power of Friendship
It's 2020 and times are tough. Maybe some of us are learning about social distancing the hard way. Maybe we just are all a little anxious. No matter what, we could probably use a friend. But what is a friend, exactly? And why do we need them so much? This week host Bethany Brookshire speaks with Lydia Denworth, author of the new book "Friendship: The Evolution, Biology, and Extraordinary Power of Life's Fundamental Bond". This episode is hosted by Bethany Brookshire, science writer from Science News.
Now Playing: Radiolab

One of the most consistent questions we get at the show is from parents who want to know which episodes are kid-friendly and which aren't. So today, we're releasing a separate feed, Radiolab for Kids. To kick it off, we're rerunning an all-time favorite episode: Space. In the 60's, space exploration was an American obsession. This hour, we chart the path from romance to increasing cynicism. We begin with Ann Druyan, widow of Carl Sagan, with a story about the Voyager expedition, true love, and a golden record that travels through space. And astrophysicist Neil de Grasse Tyson explains the Coepernican Principle, and just how insignificant we are. Support Radiolab today at