Evolution of bacteria is observed in real-time

Hyperaxion Aug 20, 2020

By analyzing 500 generations of bacteria, researchers studied how they adapt to host cells in order to survive.

A team of scientists led by Professor Matthias Horn, University of Vienna, was able to observe the evolution of bacteria in the laboratory. They intended to study how bacteria adapt to host cells. The findings were published in the scientific journal PNAS.

Evolution of bacteria is observed in real-time by scientists
Two amoebae (pink) are infected by bacteria of the genus Chlamydia (yellow/blue). (Credit: Patrick Arthofer).

The researchers observed for 14 months how a bacterium of the genus Chlamydia found in water and soil evolved within a single-celled organism.

This bacterium is not the type that causes disease in humans – it uses single-celled organisms as hosts and survives thanks to the nutrients found in it.

It serves as a model for scientists to study the adaptation of bacteria that are dependent on other microorganisms to survive.

The experiments carried out in Vienna involved 500 generations of bacteria, equivalent to a period of 15,000 years if extrapolated to the average human lifespan.

Over a year and two months of analysis, the microscopic beings were kept under two different conditions: in one, the bacteria needed to infect new host cells to survive; in the other, they could multiply permanently within the same host cell.

According to Paul Herrera, the study’s first author, the infectivity of the bacteria did not change when they were able to remain in the same host cell or their “offspring”, when the host cell divided.

“However, bacteria become increasingly infectious when they have to move from one host cell to another host cell in order to survive,” Herrera said.

Molecular level

The researchers analyzed the bacteria’s genes at the beginning of the study and compared them with the genes obtained after 500 generations. The genetic material of the two groups of bacteria was found to be significantly different at 1,161 sites.

But that was not enough to explain the differences in infectious capacity. Subsequent analyzes revealed that bacteria that needed to switch hosts to survive expressed changes in genes essential for the infection mechanism.

“The transmission pathway plays a crucial role in the development of infectivity in host-dependent bacteria,” Horn said. “These modifications result in the host cells becoming more easily infected and give the bacteria a better chance to survive outside the host cell.”

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