What is a bacteriophage?

A bacteriophage is specifically defined as a virus that infects bacteria. These viruses are highly specialized and can attach to bacterial cells, inject their genetic material, and subsequently hijack the bacterial machinery to replicate themselves. This process typically leads to the destruction of the bacterial cell, releasing new phages that can go on to infect other bacteria. Bacteriophages are significant in microbiology and have applications in research, therapy, and biotechnology.

The other choices do not align with the definition of a bacteriophage. A bacterium refers to a type of single-celled microorganism, while a fungus, which is another form of organism entirely, does not fit the criteria of being a virus or affecting bacteria specifically. A pathogenic bacterium refers to bacteria that can cause disease, but does not denote the viral nature of a bacteriophage. Thus, the only accurate description of a bacteriophage is that it is a virus that specifically targets bacterial cells.