<human>:  What are the differences between a virus and a bacterium?
<bot>: The main difference between a virus and a bacterium is that a virus is an infectious agent that lacks the ability to reproduce on its own, and requires a host cell in order to replicate, while a bacterium is an independent single-celled organism that can reproduce on its own. Additionally, viruses are much smaller than bacteria, and viruses contain genetic material, whereas bacteria do not. Viruses also typically cause diseases, while most bacteria are harmless or beneficial to humans.