Bacterial biofilms can emerge through the collective behavior of thousands or millions of cells.
Biofilms formed by Bacillus subtilis can use electric signals (ion transmission) to synchronize growth so that the innermost cells of the biofilm do not starve.
Under nutritional stress bacterial colonies can organize themselves in such a way so as to maximize nutrient availability.
Bacteria reorganize themselves under antibiotic stress.
Bacteria can swap genes (such as genes coding antibiotic resistance) between members of mixed species colonies.
Individual cells of myxobacteria coordinate to produce complex structures or move as social entities. Myxobacteria move and feed cooperatively in predatory groups, known as swarms or wolf packs, with multiple forms of signalling.
Populations of bacteria use quorum sensing to judge their own densities and change their behaviors accordingly. This occurs in the formation of biofilms, infectious disease processes, and the light organs of bobtail squid.
For any bacterium to enter a host’s cell, the cell must display receptors to which bacteria can adhere and be able to enter the cell. Some strains of E. coli are able to internalize themselves into a host’s cell even without the presence of specific receptors as they bring their own receptor to which they then attach and enter the cell.
Under nutrient limitation, some bacteria transform into endospores to resist heat and dehydration.
A huge array of microorganisms have the ability to overcome being recognized by the immune system as they change their surface antigens so that any defense mechanisms directed against previously present antigens are now useless with the newly expressed ones.
In April 2020 it was reported that collectives of bacteria have a membrane potential-based form of working memory. When scientists shone light onto a biofilm of bacteria optical imprints lasted for hours after the initial stimulus as the light-exposed cells responded differently to oscillations in membrane potentials due to changes to their potassium channels.