Bacteria possess fine tentacle-like projections that extend from their outer surface called pili. When the pili from two bacteria touch, the pilus membranes can momentarily fuse, joining the cytoplasm of the two cells together. At the moment of fusion, the two bacteria can exchange copies of their plasmids. Bacteria are also able to scarf-up free floating DNA in the environment, so plasmids released into the environment, as might occur when a cell dies and its cytoplasm leaks out, may be scavenged by other cells. However, the environment is tough on free-floating DNA and the plasmids easily break down. A third, more effective means of distributing "awareness" plasmids arose when bacteria learned how to package their plasmid DNA into protective protein shells, creating viruses. Viruses contain "information" that are released to other individual cells in the environment. Some viruses kill the cells that pick them up, while other viruses protect the cells that they "infect." Sometimes "information" is life affirming, sometimes it's lethal.

Bacterial communities evolved a means to increase their survival by deploying an polysaccharide extracellular matrix to envelope all of the cells in the community and "protect" them from the ravages of the wild environment. Individual bacteria were able to move through "irrigated" channels within the matrix. The channels also allowed a communication of extracellular materials and information molecules, which provided a communal integration among all of the members of the community. The cellular community may be populated with a variety of bacterial species. For example, oxygen-fearing anaerobic forms of bacteria can live at the bottom of a community, while oxygen-loving aerobic bacteria are present in upper levels of the same community. Bacteria within the community are readily able to exchange their DNA, and in so doing enable the cellular citizens to acquire specialized, differentiated functions.

These matrix-encased bacterial communities are called biofilms (see illustration below). Biofilms have become very important since they are now recognized to protect bacterial communities from antibiotics. The bacteria that form tooth cavities are actually biofilm communities, which resist our efforts to scour them from our teeth. The resistive and protective nature of the biofilms enabled these communities to be the first life forms to leave the ocean and live on the land.

Many years ago, biologist Lynn Margulis founded the concept that mitochondria were bacterial-like organisms that invaded the cytoplasm of more advanced nucleus-containing cells called eukaryotes. At first her ideas were ridiculed by the establishment, but over the years it has become a widely accepted belief. Interestingly, an understanding of the communal nature of bacteria in biofilms offers another interpretation.

The micrograph on the left illustrates a an example of a biofilm in a human lung. The infective pseudomonas bacterial clump is encased in a dark staining extracellular matrix ( see arrow) comprising a biofilm. Encapsulation within the matrix protects the bacteria from the immune system’s efforts to destroy them. The matrix, primarily made of carbohydrates, can also contain the muscle proteins, actin and myosin, which are found bound to the outer surfaces of some bacteria. The external actin and myosin proteins enable the bacteria to move within the film’s matrix.