Deadly bacteria were infecting primitive organisms two billion years ago

By Mark Waghorn via SWNS

Deadly bugs that kills humans were infecting primitive organisms two billion years ago, according to new research.

The first complex life on Earth was infected with ancestors of the legionella bacteria that cause Legionnaire's Disease.

Study lead author Professor Lionel Guy, of Uppsala University, Sweden, said: "Our study can help us understand how harmful bacteria arise and how complex cells evolved from simpler cells."

Scientists have long puzzled over the evolutionary shift from simple bacteria-like cells to more complex eukaryotes.

The more complex cells allowed for the transition from the simple cells that first colonized the planet to complex cellular life such as fungi, plants and animals.

Two billion years ago, ancestors of legionella bacteria already had the ability to avoid being digested by eukaryotes.

Instead, they began using eukaryotic cells - complex cells with a nucleus that make up amoebas, fungi and human beings – to multiply.

The legionella bacterium belongs to a large group called Legionellales. All Legionellales bacteria can infect eukaryotic hosts - amoebas, insects or our own cells.

Co-author Dr. Andrei Guliaev, from the same lab, said: "We discovered that the ancestor of the whole group lived about two billion years ago, at a time when eukaryotes were still in the making, evolving from simpler cells to the complex cell structure they have now.

"We believe Legionellales were among the first to infect eukaryotic cells."

The first step in an infection with legionella bacteria is for a eukaryotic host, such as an amoeba, to bring the bacterium into its cell through a process called phagocytosis.

The next step for the amoeba would be to digest the bacterium and use its parts as an energy source.

But legionella bacteria have molecular tools that keep them from being digested and allow them to instead use the amoeba as an energy source so they can multiply.

In the study, the researchers show that all Legionellales have the same kind of molecular tools as legionella.

That 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 old – when eukaryotes were in the early stages of their evolution.

Mitochondria originated from another group of bacteria and became our cells' own energy factories.

Phagocytosis is considered necessary to absorb mitochondria but is very costly from an energy standpoint.

Prof Guy said: "Some researchers believe that mitochondria were required to deliver enough energy for phagocytosis to work.

"But our results suggest that phagocytosis came first – two billion years ago – while mitochondria came later."

The study was published in the journal Molecular Biology and Evolution.