In the last three-quarters of Earth history, bacteria have become the dominant life form on the planet. They have adapted to virtually all available ecological habitats and exhibit exceedingly diverse metabolic capabilities.
Many of them are symbionts of plants and invertebrates, where they carry out important functions for the host, such as nitrogen fixation and cellulose degradation. Others can cause disease in animals, humans, or plants.
They are found almost everywhere on Earth and are essential to our food webs. In the human body, more than half of our cells are bacteria.
Some species of bacteria can communicate with each other by producing small molecules called autoinducers or pheromones that elicit reactions from the immune system in other bacteria and the innate immune system in the host. This type of communication, known as quorum sensing, is very useful for maintaining healthy populations of bacteria in biofilms and preventing the spread of disease.
Cell Wall - About 90% of all bacteria have a cell wall that protects them from damage and prevents swelling due to osmotic pressure. This wall is usually made of peptidoglycan, a polymer that forms cross-links with proteins to make it strong and stiff. Some bacteria have double walls, with a thin inner wall of peptidoglycan and an outer wall of carbohydrates, proteins, and lipids.
Cytoplasm - The cytoplasm, or protoplasm, is the gelatinous substance inside the bacterial cell membrane and contains the genetic material (DNA) and ribosomes. Ribosomes translate the genetic code from nucleic acid into amino acids, which are the building blocks of proteins.
