Microbial Exopolysaccharides

By Dr. Pooja Yadav, Assistant Professor, SHAS (Nutrition & Dietetics)

Exopolysaccharides (EPSs) are remarkable biopolymers produced by a wide variety of microorganisms, including bacteria, fungi, yeasts, and microalgae. Alongside these, natural polymers such as chitin and chitosan, typically obtained from the shells of crustaceans or the cell walls of fungi and certain yeasts, are of significant interest in the realm of biological polysaccharides. These materials are valued for their biodegradability, biocompatibility, and their ability to be transformed into functional forms like films, fibers, and membranes. Unlike chitin and chitosan which are primarily extracted from marine organisms EPSs are naturally secreted by microbes in response to environmental stress factors such as changes in temperature, salinity, pH, or exposure to chemicals and radiation. These secretions not only support microbial survival under harsh conditions but also offer substantial advantages over synthetic, petroleum-based polymers. EPSs are renewable, eco-friendly, and decompose naturally without leaving harmful residues in the environment. In terms of structural variety, EPSs can exist as capsular or slime forms. The capsular EPS forms a protective coat tightly bound to the cell surface, offering defense, while the slime type is excreted freely into the surrounding environment, aiding in microbial adhesion, biofilm formation, and protection against environmental threats. This versatility allows EPSs to be adapted for multiple applications, including biodegradable films, hydrogels, sponges, and nanocarriers for controlled delivery in pharmaceutical systems. Thanks to their functional properties and environmentally responsible profile, EPSs and related biopolymers are extensively used in fields such as biomedicine, food technology, cosmetics, and pharmaceuticals, serving as a sustainable alternative to synthetic materials.

Sources of Microbial Exopolysaccharides

Exopolysaccharides (EPSs) are naturally occurring biopolymers produced by a wide range of microorganisms, including bacteria, fungi, and algae. Among bacterial EPSs, gellan gum and welan gum are notable examples, commonly synthesized by Sphingomonas and Alcaligenes species, respectively. Fungal sources contribute EPSs such as scleroglucan, pullulan, and pleuran, which are derived from organisms like Sclerotium, Aureobasidium pullulans, and Pleurotus ostreatus. In the case of algae, EPSs like fucan, ulvan, and porphyran are produced by brown, green, and red algae, respectively. These algal polysaccharides are often sulfated, making them useful in pharmaceutical and nutraceutical applications due to their antioxidant and anticoagulant properties.

Microorganisms capable of synthesizing EPSs are commonly found in diverse ecological habitats, ranging from terrestrial to marine environments. They are frequently isolated from extreme ecosystems, including hot springs, hypersaline lakes, and deep-sea hydrothermal vents, as well as from industrial environments like wastewater treatment plants and effluents from food, pulp, and sugar-processing industries, where the carbon-to-nitrogen (C/N) ratio is typically high. These nutrient-rich yet stressful conditions often stimulate EPS production as a survival strategy. EPS-producing microorganisms span various physiological groups, including mesophiles, halophiles, and thermophiles, each adapted to specific temperature and salinity conditions. For example, Lactic Acid Bacteria (LAB) are widely recognized mesophilic EPS producers, contributing to food texture and probiotic health benefits in fermented dairy products. Similarly, certain halophilic archaea and thermophilic bacteria are known to produce EPSs with unique properties suited for industrial use under high-salt or high-temperature conditions.

Properties of microbial exopolysaccharides

Exopolysaccharides (EPSs) have garnered increasing scientific interest due to their diverse biological functions and unique chemical structures. Over the past decade, various EPSs and their modified forms have attracted attention for potential applications in medicine, food, and biotechnology. With limited discovery of new plant-derived polysaccharides, microbial fermentation has emerged as a promising and sustainable alternative for EPS production. The utility of microbial EPSs is further enhanced through structural modifications and functional derivatization, making them suitable for targeted and high-performance applications.

Antibacterial Activity

A growing body of research highlights the antimicrobial potential of EPSs. For example, EPS produced by Lactococcus lactis has shown notable antibacterial effects even at low inhibitory concentrations. Similarly, kefiran, when delivered through ultrasound-assisted methods, has exhibited antimicrobial efficacy. EPS derived from Aspergillus species, specifically DHE6, demonstrated antimicrobial effects against a broad spectrum of bacteria such as Bordetella pertussis, Pseudomonas aeruginosa, Staphylococcus aureus, and Bacillus subtilis. However, its effectiveness was limited against various strains of yeasts and fungi, indicating a selective antimicrobial spectrum.

Antioxidant Properties

EPSs also possess significant antioxidant potential. Although the exact mechanism remains unclear, their hydrogen-donating ability is believed to be central to this activity like the behaviour observed in other polysaccharide-based antioxidants. The antioxidant strength of EPSs is influenced by their monosaccharide composition, glycosidic linkage type, degree of branching, and molecular architecture. For instance, EPSs composed mainly of glucose tend to show low hydroxyl radical scavenging activity but demonstrate strong superoxide and DPPH radical scavenging abilities. Notably, EPS from Weissella cibaria SJ14, with a mannose concentration of 75.9%, showed excellent hydroxyl radical scavenging performance, comparable to standard antioxidants like ascorbic acid.

Anticancer Activity

With cancer incidence on the rise, the potential of natural agents like EPSs in prevention and treatment is of growing interest. EPS produced by Lactobacillus acidophilus has shown the ability to inhibit the growth of colon epithelial cells, and the effect increased proportionally with EPS concentration. Another study found that purified EPS fractions from Rhodococcus erythropolis HX-2 could selectively suppress the proliferation of cancer cells without significantly affecting healthy cells. Structural studies suggest that the anticancer activity of EPS is heavily influenced by its higher-order molecular architecture, including factors like helical conformation, chain flexibility, branching degree, and spatial configuration—rather than just its primary structure.

Hypocholesterolemic Effects and Cardiovascular Health

Cardiovascular disease (CVD) remains one of the leading global causes of mortality, with elevated blood cholesterol levels being a major risk factor. Socioeconomic factors also play a significant role in cardiovascular health. In this context, dietary interventions, including fermented dairy products, have shown promising cholesterol-lowering effects. Fermented milk products such as kefir, bioghurt, and acidophilus milk have been associated with reduced cholesterol levels. Specifically, milk fermented with Lactococcus lactis subsp. cremoris SBT0495 and EPS-producing Lactobacillus bulgaricus from homemade yogurt have demonstrated cholesterol-reducing potential. Although the exact mechanism remains to be fully understood, it is hypothesized that EPSs mimic dietary fibers by binding bile acids and enhancing their excretion, which in turn reduces intestinal cholesterol absorption.

Application of Microbial Exopolysaccharides

Exopolysaccharides (EPSs) possess a wide array of functional properties such as viscosity enhancement, emulsification, gelling ability, texture improvement, and immunomodulatory effects, making them valuable across numerous food and industrial domains. Their ability to influence the rheological properties of food matrices such as increasing viscosity, minimizing syneresis (water separation), and improving mouthfeel has led to their widespread use in food product development. A notable example is gellan gum, derived from Sphingomonas paucimobilis, which is widely used as a thickener, gelling agent, and emulsifier in various food systems.

Applications in Fermented and Meat-Based Foods

EPS-producing lactic acid bacteria (LAB) have applications that extend well beyond traditional dairy fermentation. In meat products, these microbes contribute to both fat reduction and textural enhancement. For example, EPS-producing strains have improved the spreadability of sausages and increased the water-holding capacity of ham, resulting in juicier products with improved sensory characteristics. Moreover, studies show that EPS-Ca6, a novel exopolysaccharide from Lactobacillus species, can effectively replace vitamin C in sausages. It reduces lipid peroxidation and oxymyoglobin oxidation, thereby improving the color stability of refrigerated meat products.

Edible Films and Packaging Innovations

EPSs are increasingly used in the formulation of edible films and biodegradable packaging aimed at enhancing food preservation. Polysaccharides like pullulan, xanthan gum, gellan gum, curdlan, bacterial cellulose, and galactopol are employed in creating both stand-alone films and edible coatings. These films are known for their excellent gas barrier properties, which help extend shelf life and maintain food quality. However, due to their hydrophilic nature, they are more suited to edible or short-term packaging. For example, kefiran has shown excellent film-forming capacity, and glycerol-plasticized kefiran films have demonstrated better flexibility and elongation than traditional materials like polystyrene and cellophane.

Dairy Products

EPS-producing microorganisms are widely employed in fermented dairy production, including cheese, yogurt, cultured cream, kefir, and milk-based desserts. These EPSs contribute to the creaminess, viscosity, and texture of dairy products by strengthening the casein network, enhancing water retention, and reducing whey separation (syneresis). They interact with milk proteins and micelles, leading to improved product consistency and desirable mouthfeel, which are key attributes in consumer acceptance.

Industrial Applications (Non-Food)

Beyond food, EPSs have notable uses in membrane technology and biomedical materials. Polysaccharides like gellan gum, curdlan, levan, hyaluronan, cellulose, pullulan, and alginates are utilized in the fabrication of filtration membranes. For instance, xanthan gum is integrated with synthetic polymers to enhance membrane strength and thickness. Researchers have created both pure EPS membranes and composite membranes, the latter combining EPSs with materials like polyether sulfone, often resulting in improved mechanical and functional properties.

Environmental Application: Heavy Metal Removal

As industrialization increases, the release of toxic heavy metals such as lead, cadmium, mercury, zinc, and nickel into soil and water systems has become a pressing environmental concern. These contaminants are persistent, non-biodegradable, and can accumulate in the food chain, leading to severe health and ecological risks. Traditional methods for removing heavy metals, such as chemical precipitation, reverse osmosis, ion exchange, and electrochemical treatments, often come with drawbacks including high costs, energy consumption, generation of secondary waste, and inefficiency at low metal concentrations. In this context, EPSs offer an effective, eco-friendly alternative for detoxifying contaminated environments.

EPSs possess a range of functional groups such as hydroxyl, carboxyl, sulfate, and phosphate moieties that enable them to bind heavy metal ions through mechanisms like ion exchange, electrostatic attraction, chelation, and surface adsorption. These properties allow EPSs to immobilize and sequester metal ions, thereby preventing their movement in soil or water and reducing their bioavailability. Various EPS-producing bacteria and fungi have been studied for this purpose, and many can form biofilms that enhance metal-binding efficiency even in extreme environmental conditions. For instance, EPS-alginate composites functionalized with urea and biuret have demonstrated a strong ability to remove nickel and zinc from aqueous systems. These bio-based materials are particularly promising for use in wastewater treatment plants, especially in industries such as mining, electroplating, and electronics manufacturing.

The advantages of EPS-based remediation go beyond just metal binding. Unlike synthetic chemicals, EPSs are biodegradable, non-toxic, and derived from renewable biological sources. This makes them a more sustainable choice for large-scale environmental applications. Additionally, EPSs can be applied in the form of gels, beads, or membranes, and can be incorporated into filtration systems to enhance performance. Their ability to operate under a wide range of pH and temperature conditions further increases their versatility in field conditions. Beyond water treatment, EPSs also show promise in soil remediation. When introduced into contaminated soil, EPSs can bind with heavy metals, reducing their mobility and limiting uptake by plants. This helps protect the food chain and contributes to the ecological restoration of degraded lands. Moreover, the presence of EPS-producing microbes in soil can improve its physical structure by enhancing aggregation and water retention, thereby promoting healthier plant growth even in previously contaminated environments.

Conclusion

Microbial exopolysaccharides (EPSs) are a versatile group of biopolymers produced by a wide range of microorganisms, and they hold immense potential in both the food and environmental sectors. These naturally occurring polymers exhibit diverse physicochemical properties, such as high water-binding capacity, emulsification, gelling ability, and stabilization, which make them suitable for numerous industrial applications. The structural complexity of EPSs is influenced by the microbial strain and the cultivation environment, giving rise to a wide array of functionalities. In the food industry, EPSs contribute significantly to enhancing product texture, viscosity, and shelf stability, serving as natural and sustainable alternatives to synthetic additives. Their incorporation into edible films and coatings offers an environmentally friendly strategy for preserving food quality, reducing spoilage, and extending shelf life. Well-known EPSs like xanthan gum and dextran are commonly used in dairy, bakery, and confectionery products to improve their rheological properties. Moreover, some EPSs possess prebiotic potential, supporting the growth of beneficial gut microbiota and promoting gastrointestinal health. In the environmental field, EPSs have demonstrated exceptional biosorption capabilities, effectively binding and removing heavy metals and other pollutants from wastewater. Their natural origin, biodegradability, and ability to function under a variety of conditions make them promising candidates for eco-friendly food innovations and sustainable environmental remediation technologies.