How Bacteria Defend Themselves Against Phages

Antibiotic resistance is a growing global health issue, with the potential to surpass cancer as a leading cause of mortality in the coming decades. Researchers at Umeå University in Sweden have explored how bacteria develop defenses against viruses, offering insights into resistance mechanisms. Their study focuses on Staphylococcus aureus, a bacterium that can cause severe infections like septic shock and pneumonia. A subset of S. aureus has become multi-resistant to antibiotics, posing significant public health risks.

The researchers examined how S. aureus defends itself against bacteriophages, viruses that infect bacteria. Bacteria and phages are engaged in an evolutionary "arms race," where phages attack bacteria, and bacteria evolve mechanisms to resist. Much of this defense is encoded in the "mobilome," a transferable part of the bacterial genome. The mobilome often carries genes responsible for toxin production and antibiotic resistance, allowing otherwise harmless bacteria to become dangerous.

Using a cryoelectron microscope, the team identified specific genes in the S. aureus mobilome that grant immunity against phages. These genes produce proteins that block phages from replicating their DNA, preventing further bacterial infection. Ignacio Mir-Sanchis, lead author on the paper published in Nature Communications, explained, "A key protein expressed by one of the genes forms a structure around an important protein encoded by the phage's genome, thereby blocking the phage's ability to copy its DNA." 

This discovery sheds light on bacterial pathogenesis and resistance. Mir-Sanchis noted, "The discovery of this mechanism could be a door opener to understand several aspects of bacterial pathogenesis. On the one hand, we now understand better how resistant bacteria defend themselves against viruses. On the other hand, because these set of genes also encode for toxins and antibiotic resistance genes, it may therefore turn out that this is an important piece of the puzzle in the fight against antibiotic resistance."