Stable communities of bacteria can resist chemical, physical, or pharmacological disturbance, whether they form photosynthetic mats on the shoreline of salty lagoons or masses of plaque on teeth. Sometimes bacteria of different kinds are attracted to one another to form a consortium inside a common slime coat. Different bacteria can act efficiently together. For example, one species will break down organic molecules, releasing hydrogen to methanogenic archaebacteria, which use the hydrogen to produce methane. Consortia of bacteria help to digest food in the stomachs of ruminants and help to form stromatolites.
Bacteria usually grow faster in consortia than they do alone.
Slime is produced by bacteria that infect wounds and diseased tissues in humans. For example, in osteomyelitis and arthritis, or where metal or plastic materials have been medically implanted in humans, bacteria often colonize exposed surfaces that are not protected by normal intact cell walls. Most serious medically, slime insulates bacteria from contact with antibiotics. Some cyanobacteria today store oxygen in bubbles in their slime coating. It s easy to imagine early cyanobacteria using their ability to tolerate oxygen, then evolving to use slime first as a defensive shield and then as an offensive weapon in the competitive environment inside stromatolites.