Animations and Visual Media
Bacterial biofilm formation
Most bacteria in aquatic environments are found in biofilms-surface-attached communities of micro-organisms, extracellular molecules and detritus – more commonly know as slime. For bacteria, life in a biofilm provides them with protection from environmental stresses such as water currents, predators, or antibiotics, and opportunities for biochemical and physiological cooperation between different organisms.
Formation of a bacterial biofilm involves a coordinated sequence of events and processes, including accumulation and multiplication of bacteria, bacterial signalling, and production of attachment molecules. The result of these combined processes is the development of a complex structure of bacterial microcolonies, microhabitats, extracellular polymers and fluid channels, filled with a dynamic community of bacteria.
Bacteria are attracted to areas with nutrients. Nutrients in aquatic habitats tend to accumulate upon surfaces, and bacteria may settle upon surfaces to take advantage of these nutrient concentrations. The accumulation and multiplication of bacteria at a site with favourable conditions results in formation of a microcolony – a growing pile of bacterial cells.
Bacteria are equipped with molecular signalling systems. Signal molecules emitted by a bacterium can be detected by other nearby bacteria. These signals allow bacteria to determine what other cells are out there and what they are doing, and are used to coordinate processes such as biofilm formation. As bacteria increase in abundance, signals will be detected at higher frequency. When signal frequency reaches a certain threshold, this may trigger a change in gene regulation and reconfiguration of cellular machinery for a new purpose, such as production of pili and extracellular polymers. This process is called quorum sensing.
Bacteria can extrude thin filamentous molecules called pili from their cell walls. Pili have an adhesive tip, can be retracted, and are used for motility and attachment. A single bacterium may have hundreds of pili. In a developing biofilm, bacteria use pili to attach themselves to other bacteria and the substrate, and to adjust their position in relation to each other.
The most characteristic feature of bacterial biofilms arises as the bacteria secrete extra-cellular polymeric substances – a mixture of polysaccharides, proteins and nucleic acids. This extra-cellular material forms a slimy matrix which cements the bacteria together and to the substrate. This gives structural support to the biofilm and helps provide resistance to external stressors.
Animations from Andrew Dopheide on Vimeo.