Striking lane-like patterns found in bacteria populations

Date:
March 22, 2022
Source:
Okinawa Institute of Science and Technology (OIST) Graduate
University
Summary:
Researchers have found that competing strains of Escherichia coli
bacteria form distinctive lane-like patterns as their populations
grow.



FULL STORY ==========================================================================
It's well understood that populations of species don't distribute
at random.

Rather, as populations grow, individuals are organized around barriers in
the landscape. This organization can be seen in, for example, the growth
of the cells around the outer layer of plants and how bacteria arrange themselves in microspores in soil. In both these cases, barriers impact
the underlying genetic diversity of the populations. These dynamics have
been well researched in larger species -- from the way plants disperse
to how barnacles spread across a rock, but they have not before been
thoroughly studied in smaller systems, like that of bacteria.


==========================================================================
Now, by combining theoretical models and experiments, scientists from the Biological Complexity Unit and the Micro/Bio/Nanofluidics Unit at the
Okinawa Institute of Science and Technology Graduate University (OIST)
have shown that, when constrained to a channel, the bacteria Escherichia
coli will form lanes of genetically similar individuals that run parallel
to the barriers. This study was published in PNAS.

"If populations grow in the presence of spatial barriers, the barriers
can constrain the movement of individuals and affect the evolution of a population," explained first author Ms. Anzhelika Koldaeva, PhD candidate
in the Biological Complexity Unit. "We found that in a channel, the
bacteria tend to align along the barriers and form patterns in their populations. Other biological systems present similar structures --
for example, bacteria in porous soil and cells growing in certain
body tissues -- so these findings can have implications for a range
of research." Escherichia coli, also known asE. coli, are rod-shaped, single-celled bacteria that are found in many different environments,
including the food and intestines of healthy people and animals. E. coli reproduce asexually with a "mother" cell splitting apart to create two "daughter" cells. To observe the population structure, two strains of
E. coliwere used, which had different fluorescence -- one was red and
the other, green. This way, the researchers could identify which daughter
came from which mother. The two strains were the same in terms of size,
the length of the reproductive cycle, and other measures of fitness.

Researchers from the Biological Complexity Unit first developed a
model for the dynamics of the colony. They simulated the growth of
the populations over several generations with the aim of experimental validations as the next step.

Then, the Micro/Bio/Nanofluidics Unit teamed up with them and took on
the experimental challenge.

"We created a microfluidic platform with a temperature and
humidity control, which contained tiny microchannels to house the
bacteria," explained Prof. Amy Shen, Principle Investigator of the Micro/Bio/Nanofluidics Unit. "This was very difficult and a lot more complicated than a standard cell experiment. We had to feed bacteria
and the system was susceptible to contamination." This process was so challenging that it took former OIST PhD student Dr. Paul Hsieh-Fu Tsai
(now an Assistant Professor at Chang Gung University in Taiwan) almost a
year to build a reliable platform for long-term imaging of the bacterial growth. For the experiments, individual bacteria from each strain were
placed approximately in the center of the microchannel and videos were
recorded over an 80-hour period to observe the patterns that formed. These videos were then analyzed and the growth dynamics from these experiments
was compared to the simulations.

Both the simulations and the experiments confirmed that, within a few generations, in the first 12 hours, the two strains of bacteria started
to form the distinctive lane-like patterns.E. coli are elongated and thus aligned themselves parallel to the sides of the microchannel. However,
the two different strains did not become mixed but rather, as time went
on, they became more segregated into their own lanes.

Prof. Simone Pigolotti, Principle Investigator of the Biological
Complexity Unit, concluded, "by using a combination of theory and
experiments, we found something unexpected in the E. colisystem, which
is used by a lot of researchers across the world."

========================================================================== Story Source: Materials provided by Okinawa_Institute_of_Science_and_Technology_(OIST)
Graduate_University. Original written by Lucy Dickie. Note: Content may
be edited for style and length.


========================================================================== Journal Reference:
1. Anzhelika Koldaeva, Hsieh-Fu Tsai, Amy Q. Shen, Simone Pigolotti.

Population genetics in microchannels. Proceedings of the National
Academy of Sciences, 2022; 119 (12) DOI: 10.1073/pnas.2120821119 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/03/220322111333.htm

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