The life cycle of a biofilm includes adhesion, aggregation, maturation and detachment or dispersion. The primary step involved in the initiation of biofilm formation is the attachment of small number of free bacterial cell known as planktonic cells, to an animate or inanimate surface with the help of pili and flagella. The attachment of cells to the substrate is known as adhesion stage which plays a vital role in growth cycle of a biofilm. Adhesion process of the planktonic cells can be carried out by primary adhesion or reversible binding and secondary adhesion or irreversible binding. As the bonding between the cells and the substrate becomes stronger, it turns into irreversibly attachment to the surface resulting in production of extracellular polymer or biofilm matrix.
Aggregation is the second stage of biofilm formation; the cells undergo cell division resulting in growth, accumulation and multiplication of cells leading to formation of microcolonies. The adherence of new planktonic cells to the already bound cells surrounded by biofilm matrix lead to further development of biofilm. The free and bound forms of bacterial cells are held together within the microcolonies by intercellular bonding, enclosed in an exopolysaccharide sheath which forms the basis of biofilm matrix, responsible for adhesion and cohesion of biofilm to the substrate.
Biofilm maturation is the third stage in process of biofilm formation. A mature biofilm is a heterogenous slimy multilayered cells embedded in an extracellular polymeric substance composed of polysaccharide (45-95%), proteins (1-60%), nucleic acids (1-10%), lipids (1-40%) and water channels. This highly hydrated channels acts as a filter allowing the transportation of nutrients and elimination of waste metabolic products across the cells that are multiplying within the biofilm. The third stage of biofilm development is maturation, a slow process and which undergoes remarkable changes in the microenvironment surrounding the bacterial cells.
Dispersion or detachment of bacteria from the biofilm structure is the last stage involved in development of biofilm. This stage can occur by different mechanisms namely seeding, erosion, sloughing and abrasion. The reason behind the detachment of cells might be the change in environmental condition, limited supply of nutrients or oxygen, cell growth or division, release of large number of individual cells or small aggregates. The rate of detachment increases with the biofilm formation.
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