Illustration of the DpK2 tail spike depolymerase from the Klebsiella pneumoniae bacteriophage. A bacteriophage, or phage, is a virus that infects bacteria, in this case Klebsiella pneumoniae. The DpK2 polymerase attacks the polysaccharides that form a protective capsule around the bacterium, allowing the phage to access cell surface receptors for entry into the cell.