Is it true that the smallest living things are bacteria which are approximately 1 micrometer in size?

The claim that bacteria are the smallest living organisms is false. There are other organisms that are smaller than bacteria, such as some viruses and archaea. One example is Nanoarchaeum equitans, a microbe that lives in hydrothermal vents and is 200 to 500 nm in diameter. It has the smallest non-viral genome ever sequenced and is recognised by Guinness World Records as the smallest living organism.  Another example is porcine circovirus, a virus that infects pigs and has a diameter of only 17 nm. This is the smallest known virus and can pass through filters that block bacteria. Bacteria are therefore not the smallest living things in the world.