Bacteria are a type of unicellular organisms that lack any membrane-bound organelle. Typically, they are few micrometers in length. They have several shapes such as spheres, rods and spirals. Bacteria were among the first life forms to appear on Earth, and they are present everywhere. Bacteria can live as free organisms, symbionts or parasites.
The number of bacteria is estimated to be ~40 million bacteria in a gram of soil and a million bacterial cells in a ml of fresh water. There are approximately 5,000,000,000,000,000,000,000,000,000,000 bacteria on Earth, forming a huge biomass. Despite their importance, ubiquitousness and abundance, how much do we know about them?