For much of microbiology’s history, microorganisms were predominantly studied as planktonic, free-floating cells, typically analyzed under laboratory conditions using nutrient-rich culture media. However, a rediscovery of an earlier observation by Antonie van Leeuwenhoek—that microorganisms readily adhere to and grow on exposed surfaces—spurred extensive research into surface-associated microbial communities, now known as biofilm. These studies revealed that biofilm-forming microorganisms exhibit distinct phenotypes compared to their planktonic counterparts, with notable differences in gene expression and growth behavior. Biofilm development involves a series of specialized mechanisms for surface attachment, establishment of a structured microbial community, and eventual detachment (biofilm dispersal).

As microbial populations increase and reach a critical density, they initiate cell-to-cell communication through a process called quorum sensing. This signaling system, mediated by chemical molecules known as autoinducers, activates genes involved in biofilm formation, differentiation, adherence, and detachment. Biofilm-associated cells differ from their free-floating forms in several key ways: the production of an extracellular polymeric substance (EPS) matrix, slower growth rates, and the selective regulation of specific genes. The attachment process is highly intricate, influenced by factors such as the characteristics of the growth medium, the substrate, and the microbial cell surface.

Mature biofilms are structured communities of microbial cells embedded in an EPS matrix, providing a robust environment for intercellular communication and horizontal gene transfer. This matrix is vital to biofilm stability and resilience, allowing the microbial community to survive in harsh conditions and resist antimicrobial treatments. The study of biofilm is particularly relevant to public health, as it is implicated in chronic infections, such as its relevance in GI disorders. Biofilm is also associated with bacterial infections involving medical devices, such as catheters and implants.

A defining feature of biofilms is their extracellular polymeric substance (EPS). This matrix constitutes 50–90% of the biofilm’s total organic carbon and serves as the primary structural component. While EPS’s chemical and physical properties vary across species, polysaccharides form the principal component. In gram-negative bacteria, EPS often contains polyanionic polysaccharides due to the presence of uronic acids (e.g., D-glucuronic, D-galacturonic, and mannuronic acids) or ketal-linked pyruvates. These anionic properties enable the binding of divalent cations like calcium and magnesium, which cross-link polymer strands, enhancing the biofilm’s mechanical strength. Conversely, EPS may exhibit a predominantly cationic composition in gram-positive bacteria such as Staphylococcus species, contributing to a different type of biofilm architecture.

The EPS matrix not only provides structural integrity but also plays a crucial role in protecting the microbial community from environmental stressors, including antibiotics, immune responses, and desiccation. Additionally, the matrix facilitates the retention of nutrients and waste products, creating microenvironments within the biofilm that support diverse metabolic activities.

Quorum sensing and autoinducers are fundamental to biofilm regulation. In gram-negative bacteria, quorum sensing is often mediated by acyl-homoserine lactones (AHLs), while gram-positive bacteria typically use oligopeptide-based signals. These molecules coordinate collective behaviors, including EPS production and biofilm dispersion, ensuring the community’s survival and adaptability under changing environmental conditions.

Conclusion

Biofilm represents a paradigm shift in our understanding of microbial life, moving beyond the simplistic view of planktonic cells to recognize the complex, cooperative, and resilient nature of surface-associated communities. Their ability to adapt through quorum sensing, EPS production, and genetic exchange highlights their ecological and clinical significance. While biofilms contribute to persistent infections and industrial challenges, they also offer opportunities for innovation, such as bioremediation and bioengineering. Continued exploration of biofilm dynamics is essential to mitigate their negative impacts while harnessing their potential in beneficial applications, making biofilm research a cornerstone of modern microbiology.