The ancestors of Legionella bacteria – which cause legionnaires’ disease – infected cells two billion years ago

Illustration of Legionella bacteria.

Researchers at Uppsala University have found that the ancestors of Legionella bacteria infected eukaryotic cells two billion years ago. This happened shortly after eukaryotes began to feed on bacteria. These results are described in a new study published in Art Molecular biology and evolutionalso contributes to the debate over chicken or egg about whether mitochondria or phagocytosis were the first.

“Our research can help us understand how harmful bacteria originate and how complex cells evolved from simpler cells,” says Lionel Guy, an associate professor of evolutionary microbiology at the Department of Medical Biochemistry and Microbiology who led the study.

Two billion years ago the ancestors of Legionella bacteria already had the ability to avoid digestion by eukaryotes. Instead, they began to use eukaryotic cells for reproduction – complex cells with a nucleus that make up amoebae, fungi and humans.

The bacterium Legionella, which causes legionnaires ’disease, belongs to a large group of bacteria called Legionellales. All Legionellales bacteria can infect eukaryotic hosts: amoebae, insects or our own cells.

Lionel Guy

Lionel Guy, Associate Professor of Evolutionary Microbiology at the Department of Medical Biochemistry and Microbiology, Uppsala University. Credit: Sanna Dovat Guy

“We found that the ancestor of the whole group lived about two billion years ago, at a time when eukaryotes were still forming, evolving from simpler cells to the complex cellular structure they have now,” said Andrei Gulyaev, a researcher at the Department of Medical Biochemistry. and microbiology. “We believe that Legionellales were among the first to infect eukaryotic cells.”

The first step in infecting Legionella bacteria is for a eukaryotic host, such as an amoeba, to transfer the bacterium into its cell through a process called phagocytosis. The next step for the amoeba will be to digest the bacteria and use its parts as an energy source. But Legionella bacteria have molecular devices that interfere with their digestion and allow them to use the amoeba instead as an energy source so they can multiply.

In the study, scientists show that all legionella have the same molecular devices as legionella. This suggests that the ability to infect eukaryotes already existed in the ancestor of all Legionellales. This means that phagocytosis is at least as old as Legionellales – two billion years – when eukaryotes were in the early stages of their evolution.

What has implications for the heated debate about chicken or egg in evolutionary biology about how eukaryotes came into being. Which came first? Were these mitochondria that originated from another group of bacteria and became our cells ’own energy factories? Or was it phagocytosis, which is considered necessary for the absorption of mitochondria, but very expensive from an energy point of view?

“Some researchers believe that mitochondria must have delivered enough energy for phagocytosis. But our results suggest that phagocytosis first appeared – two billion years ago – while mitochondria appeared later, ”says Lionel Guy.

Reference: “The adaptation of the host in Legionellales is 1.9 hectares, which coincides with eukaryogenesis” by Eric Hugheson, Andrei Gulyaev, Theo Amune and Lionel Guy on February 15, 2022, Molecular biology and evolution.
DOI: 10.1093; 10.1093 / molbev / msac037 The ancestors of Legionella bacteria – which cause legionnaires’ disease – infected cells two billion years ago

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