A slime layer is a loose, unorganized layer of extracellular polymeric substances that surrounds some bacteria and can be easily removed from the cell surface.
Explanation
Bacteria secrete extracellular polysaccharides, proteins and nucleic acids collectively known as the glycocalyx. When this material forms a thin, diffuse coating that is not tightly attached to the cell envelope, it is referred to as a slime layer. In contrast to a capsule, which is dense and firmly bound, the slime layer is amorphous and can be washed off. Slime layers protect cells from desiccation and phagocytosis, trap nutrients, and facilitate adhesion to surfaces. They are important in the early stages of biofilm formation; cells embedded in slime can move collectively across surfaces by gliding. Slime production is influenced by environmental conditions such as nutrient availability and growth rate. In clinical settings, bacterial slime contributes to persistent infections by shielding cells from antibiotics and immune factors. Industrially, slime layers and the resulting biofilms can foul pipelines and water systems.
Functions and Examples
- The slime layer helps bacteria adhere to rocks, plant roots, teeth and medical devices, serving as a scaffold for developing biofilms.
- It acts as a hydration barrier, reducing water loss and protecting against desiccation and phagocytic predators.
- By trapping extracellular enzymes and metabolites, slime layers can concentrate nutrients near the cell surface.
- Pseudomonas aeruginosa produces a mucoid slime in cystic fibrosis lungs that contributes to chronic infection.
- Dental plaque begins as a slime layer of streptococci on tooth enamel before maturing into a complex biofilm.
Although diffuse and easily removed, slime layers give bacteria a competitive advantage by promoting surface colonization and resilience. Their presence has implications for health, industry and environmental microbiology.
Related Terms: Capsule, Glycocalyx, Biofilm, Extracellular Polymeric Substance, Pellicle