Bacteria were already infecting eukaryotes two billion years ago

(ORDO NEWS) — Scientists have come to the conclusion that already two billion years ago, bacteria from the Legionellales group could infect eukaryotes by getting inside their cells in the process of phagocytosis. The discovery provides new evidence that phagocytosis predates mitochondria.

Researchers from Uppsala University (Sweden) concluded that the ancestors of the pathogenic gram-negative bacteria Legionella’s ( Legionellales ) began to infect eukaryotic cells two billion years ago. Unlike prokaryotes, which include bacteria, eukaryotes contain a nucleus and other complex structures in their cells.

These organisms appeared on Earth much later than prokaryotes, two billion years ago, their history was just beginning.

The results of the study, published in the journal Molecular Biology and Evolution, help to better understand the co-evolution of eukaryotes and their pathogenic bacteria, and also contribute to the debate about which came first – mitochondria or phagocytosis.

Legionellales are a broad group of pathogenic bacteria that infect many eukaryotic organisms. Including its representatives become the cause of acute infectious human diseases. The best known among them are Legionella pneumophila , the causative agent of Legionnaires’ disease, and Legionella longbeachae , which causes Pontiac fever.

Modern Legionella enter the cell during phagocytosis – the process of absorption and digestion of solid particles by eukaryotic cells. Bacteria have specialized molecular mechanisms that allow them to remain intact inside the host cell and use its energy resources for their reproduction.

By researching Legionellales , scientists have shown that all members of the group have molecular tools to keep them from being digested inside the host cell.

This suggests that the ability to infect eukaryotes already existed in the common ancestors of modern Legionella, who lived two billion years ago. Probably, these bacteria became one of the first parasites of cellular organisms.

The new findings are relevant in the context of a longstanding scientific debate about which came first, mitochondria or phagocytosis.

This question is reminiscent of the chicken-and-egg paradox. Mitochondria are cellular organelles in which organic compounds are oxidized and ATP is synthesized – a universal energy source for almost all biochemical processes.

According to the most popular hypothesis of the origin of mitochondria – the theory of symbiogenesis – they, like plant chloroplasts, originated from bacteria absorbed by a eukaryotic cell. This process would require phagocytosis, which requires so much energy that its existence is difficult to imagine in cells without mitochondria.

The results of the new study suggest that phagocytosis appeared before mitochondria. At the very least, this process must be as ancient as the bacteria Legionellales .

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