Bacterial extracellular polymeric substances: Biosynthesis and interaction with environmental pollutants (2023)


Bacteria exhibit either planktonic (free-living) or sessile (surface-attached) modes of growth. Surface-attached mode of growth develops into structured communities of bacteria encased within a self-produced extracellular polymeric substances (EPS) matrix called biofilm (Rumbaugh and Sauer, 2020). EPS are high molecular weight polymers produced by bacteria, mainly composed of polysaccharides, proteins, lipids, and DNA. These polymers are the most abundant component of the biofilm that provide viscoelasticity, cohesion, protection, and nutrition to the bacteria. EPS is referred to as the “dark matter of biofilm” since only the polysaccharides component of the EPS is well studied. In contrast, other EPS molecules are less explored and cannot be characterized as either carbohydrates, proteins, or lipids (Flemming, 2016; Decho and Gutierrez, 2017). Polysaccharides are present in more amounts and are widely studied components of EPS that vary immensely in structure and function. Molecular weight of EPS ranges from 10 to 1000kDa; however, the chemical nature of EPS varies depending on the species-specific monosaccharides and non-carbohydrate substituents (Jiao et al., 2010; Nwodo et al., 2012). The difference in structure is based on the composition of monosaccharides, chain length, and branching. Extracellular polysaccharides produced by most bacteria range from linear homopolymers (e.g., dextran, curdlan, cellulose) to branched heteropolysaccharides containing three or more monosaccharides (e.g., alginate, xanthan, gellan, emulsan) arranged in a group to form repeating units (Lembre et al., 2012; Khan et al., 2022).

Structural and functional diversity of bacterial extracellular polysaccharides mainly depends on the organization of extracellular polysaccharide genes. Extracellular polysaccharides operon comprises an organized set of genes that regulate EPS synthesis, determine chain length, formation of repeat units, and polymerization and transport of the repeating units. Enzymes for synthesizing nucleotide sugar precursor and nucleotide sugar precursor molecules are crucial for the biosynthesis of extracellular polysaccharides. It has been observed that the over-expression of genes involved in extracellular polysaccharides assembly caused an enhanced yield of EPS (Vandana and Das, 2022).

Extracellular polysaccharides biosynthesis is a multistage process where extracellular polysaccharides are intracellularly synthesized and exported outside. The biosynthesis process starts with the forming of precursor sugar nucleotide (UDP-galactose, UDP-glucose, and dTDP-rhamnose) that forms repeating units. Modification of the extracellular polysaccharides is facilitated with the action of hydrolases and transferases by adding pyruvate, glycerate, succinate, or acetate. Biosynthesis and transport into the extracellular environment are facilitated by three pathways, Wzx/Wzy-dependent pathway, ABC transporter-dependent pathway, and the synthase-dependent pathway (Schmid et al., 2015). Extracellular polysaccharide polymers contain charge, apolar groups such as carboxyl, hydroxyl, sulphydryl, sulfate, phosphate, and hydrophobic regions. In addition, the protein components contain carbonyl and amino groups, while eDNA only contains hydrophobic and phosphate regions. These functional groups play a diverse role, such as nutrient acquisition and bioremediation of toxic pollutants (Wiśniowska and Kowalczyk, 2022).

EPS has a distinct sorption mechanism and binding sites (cationic and anionic), which help remove inorganic and organic pollutants. Bacterial EPS is involved in processes such as bioaccumulation and biosorption of inorganic compounds and degradation of organic compounds to reduce them to CO2, H2O, and CH4 with the help of enzyme activity (Mohapatra et al., 2020). Anionic functional groups of EPS form organometal complexes with metal ions by electrostatic interaction Priyadarshanee and Das, 2021a. In addition, hydrophobic functional groups in EPS bind with the organic pollutants by hydrophobic-hydrophobic interaction, which helps accumulate organic pollutants. Thus, bacterial biofilm-EPS-mediated bioremediation is a cost-effective, sustainable, and eco-friendly technique for restoring the contaminated environment.

Although the properties and biosynthesis mechanism of the extracellular polysaccharides component of EPS have been extensively reviewed, the role of EPS components in the interaction with environmental pollutants has not been reviewed yet. This review summarizes the properties and characterization of EPS based on various analytical techniques. Biosynthesis of extracellular polysaccharides through central carbon metabolic intermediates has been discussed elaborately. Further, the interaction mechanism of EPS matrix components with toxic pollutants has been discussed. In addition, the bioremediation of environmental pollutants by extracellular polymers has been reviewed comprehensively.

Section snippets

Structure and properties of bacterial polymer

Biopolymers are biomolecules containing monomers joined by covalent bonds to form a long chain of molecules. The prefix ‘bio’ suggests that molecules produced by bacteria are biodegradable (Mohan et al., 2016). Polymer produced by bacteria is highly hydrated, gel-like, three-dimensional matrices called EPS that trap the bacteria.

EPS comprises a wide variety of biopolymers such as polysaccharides, proteins, lipids, and eDNA that interact with each other and provide structural stability to the


Extracellular polysaccharide is the major component of the EPS. EPS includes common carbohydrates like d-mannose, d-glucose, d-galactose, d-mannuronic acid, d-galacturonic acid, d-glucuronic acid, l-fucose, l-rhamnose, l-guluronic acid, N-acetyl-d-galactosamine, and N-acetyl-d-glucosamine (Sutherland, 2001, 2016). Composition and chemical properties of extracellular polysaccharides contribute to the functionality of biopolymers. It offers various functional roles, such as adherence to the

Biosynthesis of extracellular polysaccharides

Biosynthesis of extracellular polysaccharides occurs intracellularly and transports across the bacterial cell membrane; however, synthesis of some homopolysaccharides, such as levan, mutan, and dextran, occurs outside the cell. These exceptional homopolysaccharides are synthesized through extracellular secreted enzymes like glycosyltransferases (GTs) that act on the carbon substrate to convert into the polymer (Li and Wang, 2012). Apart from the simpler synthesis of these few

Interaction of polymers with environmental pollutants

Bacterial extracellular polymers sequester environmental contaminants by different mechanisms leading to superior removal efficiencies. Polysaccharides and proteins, the main constituents of the EPS, are significantly involved in interacting with environmental contaminants. Functional groups of the EPS having negative charge electrostatically attract the positively charged heavy metals (Huangfu et al., 2019). Metals interact with polyanionic EPS with varying degrees of affinity and selectivity.


Bacteria with aggregation or adhesion ability to a surface secrete a gelatinous matrix of EPS to construct biofilm. Extracellular polysaccharides interact among themselves as well as with other extracellular polymers such as proteins and eDNAs, providing essential structure and stability to biofilm. EPS production and secretion are based on the EPS genetic organization of the bacteria. The operon of extracellular polysaccharide involves functional genes, including GTs, polymerase, export, and

Credit author statement

Vandana: Writing – original draft, drawing of figures. Monika Priyadarshanee: Writing – original draft, drawing of figures. Surajit Das: Funding acquisition, Conceptualization, Supervision, Reviewing and Editing.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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Authors are thankful to the authorities of NIT Rourkela for providing research facilities. SD acknowledges the funding agency Department of Science and Technology, Government of Odisha [No. 1203/ST- (Bio)- February 2017 and ST-BT-MISC-0009-2022-2744/ST]. MP acknowledges the Department of Science and Technology, Govt. Of India, for providing INSPIRE Award (No. DST/INSPIRE Fellowship/2017/IF170195) for the doctoral study.

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What are extracellular polymeric substances in bacteria? ›

Extracellular polymeric substances (EPS) are organic polymers of microbial origin involved in bacterial cells' interactions with their environment [1]. EPS are comprised of polysaccharides, proteins, extracellular DNA (eDNA), and lipids.

What do the extracellular polymeric substances EPS do for the bacteria in a biofilm community? ›

Extracellular polymeric substances (EPSs) are natural polymers of high molecular weight secreted by microorganisms into their environment. EPSs establish the functional and structural integrity of biofilms, and are considered the fundamental component that determines the physicochemical properties of a biofilm.

What are the functions of extracellular polymeric substances? ›

Extracellular polymeric substances are responsible for the cohesion of microorganisms and adhesion of biofilms to surfaces, influencing spatial organization, allowing interactions among microorganisms, and acting as adhesives between cells (Wolfaardt et al., 1999).

Why do bacteria produce EPS? ›

The production of EPS is not only an advantage to the microbes but also to the soil environment in general. The adhesiveness is important for gluing soil particles together; high water holding capacity protects microorganisms and plants against drought, as well as permits the diffusions of nutrients in the environment.

What are extracellular bacterial infections examples? ›

Staphylococcus aureus, Streptococcus pyogenes, Pseudomonas aeruginosa, Escherichia coli are typical examples of bacteria which have been labeled extracellular pathogens, and wound infections, osteomyelitis, scarlet fever, certain forms of pneumonia, urinary tract infections are examples of infections caused by these ...

What are the 3 main extracellular materials? ›

Extracellular matrix is composed of three main proteins, namely, collagen, non-collagen and proteoglycan.

What is the main purpose of extracellular enzymes for bacteria? ›

Extracellular enzymes are produced by microbes to degrade complex organic matter into useable products that can be taken up across the cell membrane. These enzymes are required to access resources in chemically complex polymers, but they are also costly to synthesize and secrete (Koch, 1985).

Which of the following best describes why extracellular polymeric substances are important? ›

Which of the following best describes why extracellular polymeric substances are important? They are components of a biofilm secreted by the microbes present.

What are extracellular polymeric substances in wastewater? ›

EPS are a complex high-molecular-weight mixture of polymers excreted by microorganisms, produced from cell lysis and adsorbed organic matter from wastewater.

What is an example of a polymeric substance? ›

Polymers make up many of the materials in living organisms, including, for example, proteins, cellulose, and nucleic acids. Moreover, they constitute the basis of such minerals as diamond, quartz, and feldspar and such man-made materials as concrete, glass, paper, plastics, and rubbers.

What are two roles of extracellular components? ›

The extracellular matrix not only provides structural support to cells and tissues, but also plays important roles in regulating the behavior of cells in multicellular organisms.

What is the role of EPS in plant growth? ›

EPS and capsular polysaccharides represent the major components of biofilm and participate in cell-cell aggregation that is crucial for bacteria anchoring and adhesion to plant roots [127,128]. Therefore, the absence of EPS affects biofilm formation and root colonization, which may impact drought resistance in plants.

How do you extract EPS from bacteria? ›

3.1. 4 Heating Method
  1. Heat the bacterial culture at 80 °C for 10 min.
  2. Centrifuge the mixture at 11,180 × g for 10 min.
  3. Filter the supernatant with 0.45 μM acetate cellulose membranes.
  4. Finally, remove the extracting reagent in the EPS solution by membrane dialysis (3500 Da) for 24 h at 4 °C.
Dec 4, 2020

What are the conditions required for EPS production? ›

Optimization of cultural conditions shows that EPS production is dependent on temperature, initial pH, and concentrations of carbon, nitrogen, and phosphate in the medium.

How is EPS formed? ›

EPS is manufactured from styrene monomer; low levels of styrene occur naturally in many plants, fruit, vegetables, nuts and meat. EPS is a derivative of ethylene and benzene and is made using a polymerisation process which produces translucent spherical beads of polystyrene, about the size of sugar granules.

What kills extracellular bacteria? ›

Extracellular pathogens are dispatched by a combination of direct killing (NK cells and complement) and ingestion (macrophages and neutrophils).

What cells destroy extracellular bacteria? ›

Neutrophils, dendritic cells and macrophages release chemicals to stimulate the inflammatory response. Neutrophils and macrophages also consume invading bacteria by phagocytosis.

How do extracellular bacteria avoid killing? ›

iv) Avoid Phagocytosis

Some non-encapsulated extracellular bacteria avoid capture by phagocytes by temporarily entering non-phagocytes such as epithelial cells and fibroblasts.

What are 5 examples of extracellular fluids? ›

The extracellular fluid, in turn, is composed of blood plasma, interstitial fluid, lymph and transcellular fluid (e.g. cerebrospinal fluid, synovial fluid, aqueous humour, serous fluid, gut fluid, etc.). The interstitial fluid and the blood plasma are the major components of the extracellular fluid.

What is the most common form of extracellular material? ›

Collagen. Collagens are the major structural component of the ECM1. They are the most prevalent protein in the skin and bone, making up 25% of the total protein mass2.

What is the extracellular substance made of? ›

The extracellular matrix of connective tissue is composed of fibers and ground substance. In ordinary connective tissue, the principal fiber type is collagen (the most abundant protein in the body), with elastic fibers as a minor element; ground substance consists mainly of water.

Do extracellular enzymes make bacteria more pathogenic? ›

Overall, while the impact of extracellular enzymes on pathogenicity can vary, they are generally thought to make a bacterium more pathogenic by facilitating invasion, evasion, and spread within the host.

Would extracellular enzymes make bacteria more pathogenic Why? ›

Do you think extracellular enzymes would make a bacteria more or less pathogenic? More pathogenic because exoenzymes can degrade the extracellular matrix that holds tissues in the body together.

Which bacteria produce extracellular enzymes? ›

Heterotrophic bacteria have the ability to produce extracellular enzymes (protease enzymes, amylases, and cellulases) that are necessary for the bioremediation of organic waste.

What are the two most significant extracellular ions? ›

Within the extracellular fluid, the major cation is sodium and the major anion is chloride.

What are the advantages of extracellular? ›

These extracellular, membrane-bound organelles can perform a variety of functions, including binding and delivery of DNA, transport of virulence factors, protection of the cell from outer membrane targeting antimicrobials, and ridding the cell of toxic envelope proteins.

What is the importance of this polymeric matrix for the biofilm microbes? ›

The polysaccharide component of the matrix can provide many diverse benefits to the cells in the biofilm, including adhesion, protection, and structure. Aggregative polysaccharides act as molecular glue, allowing the bacterial cells to adhere to each other as well as surfaces.

What is polymer used for in wastewater treatment? ›

As you can tell, polymers play an important role in wastewater treatment. Besides separating solids from liquids, they also help thicken sludge and dewater contaminated material for easier handling and disposal. Removing the water content from a waste sludge can change the waste properties from liquid to solid waste.

What are examples of extracellular materials? ›

Here, we are going to include the cell wall as a type of extracellular matrix, although animal and plant cell extracellular matrices are really different.
  • Cell wall. Cell wall. ...
  • Basal lamina. ...
  • Connective proper. ...
  • Tendon. ...
  • Cartilage. ...
  • Bone. ...
  • Nervous tissue. ...
  • Blood serum.
Apr 2, 2023

Where are extracellular substances found? ›

Extracellular polymeric substances are generally present at the exterior of cells, generated through active secretion, cell lysis, shedding of cell surface material, and also adsorption from the environment [53,54].

What are the 4 types of polymers? ›

The four basic polymer structures are linear, branched, crosslinked, and networked.

What are 3 common polymers? ›

Examples of synthetic polymers include nylon, polyethylene, polyester, Teflon, and epoxy. Natural polymers occur in nature and can be extracted. They are often water-based. Examples of naturally occurring polymers are silk, wool, DNA, cellulose and proteins.

What are 3 examples of polymers that you use daily? ›

Product made from polymers are all around us: clothing made from synthetic fibers, polyethylene cups, fiberglass, nylon bearings, plastic bags, polymer-based paints, epoxy glue, polyurethane foam cushion, silicone heart valves, and Teflon-coated cookware.

How can cells interact with the extracellular environment? ›

Cells interact with the extracellular environment through cell adhesion molecules, e.g., integrins. This interaction affects the formation of cell adhesions and the cytoskeleton. Embedded within adhesions and the cytoskeleton are signaling molecules that will affect biochemical pathways depending on how cells adhere.

What is the function of extracellular environment? ›

The extracellular structures may fulfill relevant roles in terms of structure and functional organization, contributing to fundamental processes like cell adhesion, migration, proliferation, differentiation, and apoptosis.

How do cells interact with extracellular materials? ›

Cell-matrix adhesion is the interaction of a cell with the extracellular matrix, mediated by multi-protein adhesion structures such as focal adhesions, fibrillar adhesions and podosomes. The ECM is a network of extracellular molecules which are secreted locally to ensure cell and tissue cohesion.

What is EPS in environmental science? ›

Extracellular polymer substance (EPS) is a potential bio-flocculant. • EPS is environmental friendly, non-toxic, and biodegradable. • Identification of EPS producing bacteria using different techniques are presented.

What does EPS stand for in environmental science? ›

Nationwide Environmental Protection Services (EPS) PCB Alternative Disposal Approval and Notifications | US EPA.

What are the biological activities of EPS? ›

The structure of the marine microbial Exopolysaccharides (EPS) is complex and diverse, and is linked to various biological activities, such as antibacterial, antioxidant, anti-cancer, antifreeze, anti-inflammatory, enhancement of immune activity and blood pressure, and lipid reduction.

Which bacteria produce EPS? ›

Among EPS producing bacteria, Lactic acid bacteria (LAB) have has grasped the attention of researchers thank to their strong ability to produce EPSs. The LAB strains as Streptococcus, Lactococcus, Pediococcus, Lactobacillus, Leuconostoc and Weissellale are often used to produce EPSs [7].

Is EPS secreted by bacteria? ›

Extracellular polymeric substances (EPS) are organic polymers of microbial origin involved in bacterial cells' interactions with their environment [1]. EPS are comprised of polysaccharides, proteins, extracellular DNA (eDNA), and lipids.

What factors affect EPS production? ›

bulgaricus. The factors found to affect EPS production in this medium were oxygen, pH, temperature, and medium constituents, such as orotic acid and the carbon source.

Why do we need EPS? ›

EPS helps investors understand whether investing in a particular company is profitable.

Is it mandatory to have EPS? ›

Employee Pension Scheme applies to those persons who are members of EPFO (Employee Provident Fund Organisation). Moreover, they contribute to the EPS account. For salaried employees earning up to ₹15,000, it is compulsory. Moreover, employees with a salary of more than ₹15,000 can contribute voluntarily.

What are 3 characteristics of EPS? ›

EPS products are comprised of 98% air, so they have excellent insulation and shock-absorbent properties. Furthermore, it is used in various industries because it has great lightness, processability, and durability. Also, due to it being a single material, it is easy to recycle.

What are the two types of EPS? ›

There are two different types of earnings per share: basic and diluted. Reporting basic EPS is required because it increases the comparability of earnings between different companies. Diluted EPS is required to reduce moral hazard issues.

What are the extracellular components of bacteria? ›

The extracellular matrix of bacterial biofilms is commonly composed of proteins, exopolysaccharides, nucleic acids, lipids and other minor biomolecules such as secondary metabolites.

What is the extracellular part of bacteria? ›

Many bacteria secrete extracellular polymers outside of their cell walls called glycocalyx. These polymers are usually composed of polysaccharides and sometimes protein. Capsules are relatively impermeable structures that cannot be stained with dyes such as India ink.

What are the extracellular structures of bacteria? ›

The extracellular matrix (ECM) is a mixture of secreted high-molecular-weight polymers produced by nearly all types of cell. In bacteria, it consists of three major components: polysaccharides, proteins, and extracellular DNA.

What are extracellular enzymes in bacteria? ›

Extracellular enzymes are produced by microbes to degrade complex organic matter into useable products that can be taken up across the cell membrane. These enzymes are required to access resources in chemically complex polymers, but they are also costly to synthesize and secrete (Koch, 1985).

What are the three main types of extracellular structures? ›

It is composed of three categories of materials:
  • Glycosaminoglycans and their proteoglycansthat resist compressive forces.
  • Adhesive glycoproteins (laminin, fibronectin, tenascin, nidogen)
  • Fibrous proteinsthat provide tensile strength (collagens, elastin)

What two components are commonly found in the extracellular? ›

Two main classes of extracellular macromolecules make up the matrix: (1) polysaccharide chains of the class called glycosaminoglycans (GAGs), which are usually found covalently linked to protein in the form of proteoglycans, and (2) fibrous proteins, including collagen, elastin, fibronectin, and laminin, which have ...

What extracellular structure allows bacteria to move? ›

Two types of surface appendage can be recognized on certain bacterial species: the flagella, which are organs of locomotion, and pili (Latin hairs), which are also known as fimbriae (Latin fringes). Flagella occur on both Gram-positive and Gram-negative bacteria, and their presence can be useful in identification.

Why are bacteria extracellular? ›

Main. Bacteria have historically been divided into two distinct groups: extracellular bacteria, which exist as free-living organisms in their environmental niches, and intracellular bacteria, which infect and replicate inside host cells.

What is the response to extracellular bacteria? ›

In an infection by extracellular bacteria, the host triggers a series of responses to combat the pathogen and prevent its spread. The main mechanism of the innate immune response to eradicate bacteria is activation of the complement system, phagocytosis, and inflammatory response (Figure 1).

How do bacteria do extracellular digestion? ›

Bacteria feed by the process of extra- cellular digestion. This occurs by the bacterial cell secreting digestive enzymes into the food source outside the bacterial cell. The digestive enzymes break down the food source (e.g. some warm chicken) and reabsorb the digested molecules into the bacterial cell.

Do all bacteria use extracellular digestion? ›

Unlike humans, a bacterium is an individual cell. This means that it must feed by extracellular digestion. Extracellular digestion involves enzymes being allowed out through the cell membrane and being secreted onto food molecules.

What is the structure and function of extracellular materials? ›

A large network of proteins and other molecules that surround, support, and give structure to cells and tissues in the body. The extracellular matrix helps cells attach to, and communicate with, nearby cells, and plays an important role in cell growth, cell movement, and other cell functions.

What is the role of extracellular enzymes in bacterial metabolism in an ecosystem? ›

Extracellular enzymes help microbes to digest and utilize fractions of organic matter, including EPS, which can stimulate growth and enhance microbial activity.


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