User:Parismm/Extracellular polymeric substance

The first step in formation of Biofilms is adhesion. The initial bacterial adhesion to surfaces involves the classic adhesin–receptor interactions. Polysaccherides, lipids and proteins in the matrix all can function as the adhesive agents. EPS also promotes cell–cell cohesion (including interspecies recognition) to facilitate microbial aggregation and biofilm formation. Other interspecies interactions depend on mechanosensors or specific adhesin (protein)–receptor (saccharide) pairs. In general, the EPS-based matrix mediates biofilm assembly as follows. (i) The EPS formed at the site of adhesion (produced on bacterial surfaces or secreted on the surface of attachment) form an initial polymeric matrix promoting microbial colonization and cell clustering. (ii) Continuous EPS production in situ further expands the matrix three-dimensionally while forming a core of EPS-enmeshed bacterial cells. (iii) This core provides a supporting framework, facilitating the development of 3D clusters and aggregates (or microcolonies). Minerals are the result of biomineralization processes tightly regulated by the environment or bacteria and serve as an essential component of the EPS. They also provide structural integrity to biofilm matrix and act as a scaffold to protect bacterial cells from shear forces and antimicrobial agents. Afterwards, as biofilm becomes established, an essential physical feature of EPS is to provide physical stability and resistance to mechanical removal, antimicrobials, and host immunity. EPS-associated viscoelasticity of mature biofilms (afforded by exopolysaccharides and eDNA) makes their detachment from the substratum challenging even under sustained fluid shear stress or high mechanical pressure. In addition to mechanical resistance, EPS also promote protection against antimicrobials and enhanced drug tolerance. EPS can act as a diffusion-limiting barrier against various antimicrobials resulting in limited drug access into the deeper layers of the biofilm. Retarded penetration due to the reaction of antimicrobials with EPS components, (e.g., positively charged agents likely bind to negatively charged polymers) also contributes to the antimicrobial tolerance of biofilms, enabling inactivation or degradation of antimicrobials by enzymes present in biofilm matrix. Another prominent chemical function of the biofilm matrix is its role as local nutrient reservoir of various biomolecules, for example, fermentable polysaccharides. A recent report revealed that due to osmotic pressure differences in V. cholerae biofilms, the microbial colonies physically swell, thereby maximizing their contact with nutritious surfaces and thus, nutrient uptake. However, it is important to keep in mind that biofilm formation may be essential for some beneficial functions. B. subtilis, for example, has gained interest for its probiotic properties as it can effectively maintain a favorable balance of microflora in the gastrointestinal tract. In order to survive processing and storage of food, as well as passage through the upper gastrointestinal tract, B. subtilis produces an extracellular matrix that protects it from stressful environments. In addition, B. subtilis can effectively protect plants against diverse microbial threats. The protein matrix component TasA and the exopolysaccharide have both been shown to be essential for effective plant-root colonization in both Arabidopsis and tomato plants.

Function[edit][edit]
Production of EPS followed by adhesion to the surface give rise to the formation of biofilm. compositional support as well as protection of microbial communities from the harsh environments are the major roles of matrix which compromises EPS. One of the challenges of EPS-enriched biofilms is regarding its formation on implant surfaces which would contribute to microbial accumulation, cross-kingdom interaction, antimicrobial resistance, biofilm virulence, and, consequently, peri-implant tissue damage. In 1960s and 1970s, light was shed on the presence of exopolysaccharides in the plaque associated with tooth decay. In the field of paleomicrobiology, dental biofilms and their EPS components on provide the scientists with information about the composition of ancient microbial and host biomolecules as well as the diet. Minerals in EPS were found to contribute to morphogenesis of bacteria (in Bacillus subtilis and Mycobacterium species), structural integrity of the matrix and also associate with medical conditions e.g. calcite generated by Pseudomonas aeruginosa, calcium and magnesium causing catheter encrustation in the biofilms of Proteus mirabilis, Proteus vulgaris, and Providencia rettgeri, presence of CaCO3 in the matrix of B. subtilis and Mycobacterium smegmatis biofilms.

New Approaches to target Biofilms[edit]
Application of Nanoparticles are one of novel techniques to target biofilms due to their high surface-area-to-volume ratio, their ability to penetrate to the deeper layers of biofilms and the capacity to releasing antimicrobial agents in a controlled way. Studying NP-EPS interactions would provide deeper understanding to develop more effective NP. Some factors that would alter the potentials of the NP to transport antimicrobial agents into the biofilm include physicochemical interactions of the NPs with EPS components, the characteristics of the water spaces (pores) within the EPS matrix and the EPS matrix viscosity. Size and surface properties (charge and functional groups) of the NPs are, respectively, the major determinants of the penetration in and the interaction with the EPS.

nanomaterials could provide alternative ways to control EPS-mediated biofilm virulence. For example, on-demand 'smart release' nanocarriers that can penetrate biofilms and be triggered by pathogenic microenvironments to deliver drugs or multifunctional compounds (from catalytic nanoparticles to aptamers, dendrimers, and bioactive peptides) have been developed to disrupt the EPS and the viability or metabolic activity of the embedded bacteria. The use of probiotics or phage therapy targeting EPS has also been considered as potential antibiofilm strategies.

approaches focused solely on EPS degradation (or antimicrobial activity) may not achieve efficacy within the complex (physicochemical) biofilm microenvironment. Prospective therapeutic strategies need to target simultaneously the biofilm matrix components and the embedded microorganisms to eradicate the pathogenic niche with minimal cytotoxicity to surrounding tissues.

EPS in Microalgal Biofilms
EPS is also present in the microalgal biofilm in which the algae cells encase themselves. Formation of Biofilm starts with reversible absorption of floating to the surface, then followed by production of EPS the adsorption will get irreversible. EPS will colonize the cells at the surface with hydrogen bonding. Replication of early colonizers will be facilitated by the presence of organic molecules at the surface. As the colonizers are reproducing, the biofilm grows and becomes a 3-dimensional structure. Microalgal biofilms consist of 90% EPS and 10% algal cells. algal EPS has similar components to the bacterial one; it is made up of proteins, phospholipids, polysaccharides, nucleic acids, humic substances, uronic acids and some functional groups, such as phosphoric, carboxylic, hydroxyl and amino groups. Algal cells consume EPS as their source of energy and carbon. Furthermore, EPS protects them from dehydration and reinforces the adhesion of the cells to the surface. In algal biofilms, EPS has two sub-categories; soluble EPS (sEPS) which is the and bound EPS (bEPS) with former being distributed in the medium and the latter being attached to the algal cells. Bounded EPS can be further subdivided to tightly bounded EPS (TB-EPS) and loosely bounded EPS (LB-EPS). Several factors contribute to the composition of EPS including species, substrate type, nutrient availability, temperature, pH and light intensity.