Exopolysaccharide, a.k.a extracellular polymeric substances or EPS, are complex carbohydrates derived from variable carbon sources produced by microorganisms of all taxa such as bacteria, fungi and algae, which are secreted outside into the external environment, either in the form of loosely bound slime or a jellylike substance or a tightly bound capsule.
They are formed by polymerisation of sugar residues such as glucose, galactose, glucosamine, and mannose with varying proportions and may be homopolysaccharides (HoPs) and heteropolysaccharides (HePs) with molecular weight ranging from 10 to 1000kDa.
Lipids, nucleic acid, proteins, lipopolysaccharide and minerals are components which may constitute in the formation of EPS. These macromolecules are produced as a biological response to unfavourable micro and macro environmental conditions, nutrient absorption and cellular interactions.
Glucan exopolysaccharide which is a polysaccharide derived from glucose was termed as dextran and was isolated from Leuconostoc mesenteriodes. Thereafter, multiple exopolysaccharides were uncovered and isolated, some of which included cellulose, xanthan, kefiran, gellan and alginate.
Certain plants, algae and microorganism produce a viscous water-soluble polysaccharide called mucilage, which is a mixture of EPS with minimal amount of protein such as polar glycoproteins or lectins that act as a repository of water and nutrients, agglomeration of membranes and facilitating seed germination and seed establishment through variable methods of seed dispersal and rhizosphere modification. Examples include succulents such as cacti, flaxseed (Linum usittatissimum), marshmallow (Althea officinalis) and legumes.
Protists like diatoms perform mucilage propulsion as a mode of locomotion where secretion of mucilage is inverse with respect to the direction of propulsion. Exopolysasccharides are also referred to as virulence factors which play a significant role in enhancing expression of virulence in bacteria by augmenting their ability to circumvent around the innate immunity of the host. This was tested by the of utilisation of EPS producing strain which led to abscess formation in mice and was capable to avoid response from human polymorphonuclear leukocytes.
In nature, bacteria grow in colonies which interact with one other in the form of poly-microbial aggregates as opposed to lab grown counterparts which are isolated and dispersed throughout the culture. These aggregates are encased in hydrated extracellular polymer (EPS) consisting of extracellular DNA, lipids and saccharides. Biofilms have thus been dubbed as “city of microbes” and the constituting exopolysaccharide as “house of biofilms”.
Biofilms have been extensively studied due to the significance found in processes such as adhesion, protection, binding and absorption but it also plays a pivotal role in human diseases such as cystic fibrosis pneumonia, biliary tract infections, otitis media and musculoskeletal infections. Extensive research is being undertaken in this field, primarily using encapsulated, gram-negative Pseudomonas aeruginosa which has been attributed as the Escherichia coli of biofilm research.
Bacterial exopolysaccharide has been under a thorough investigation to be used in bioremediation processes due to the ability to bind to cations and absorb charged particles(ions) via active and passive transport. They possess a great potential in sewage treatment, mining and industrial waste as metal binding sites of EPS can be manipulated by level of acetylation such that it may be utilised in extraction of heavy metals from waste.
EPS produced by latic acid bacteria is responsible for production of dairy products such as flavoured yogurts, cheeses and fermented cream. It is used in food, beverages and detergents as texturizers and stabilizers, which amplify the quality of processed food products. Biocompatibility and biodegradability of some exopolysaccharide have prompted their use in medical application such as formation of matrices in tissue engineering, wound healing and drug delivery.
Exopolysaccharides such as chitosan, mauran and shizophyllan show remarkable drug carrier properties whereas hyaluronic acid and pullulan can act as antitumor targeting agents with nanocarrier properties, which can overcome limitations of chemotherapeutic drugs.
Thus, exopolysaccharide may act as a viable alternative to products derived from plant and animal which will substantially decrease the levels of carbon footprint as well as the number of pollutants which are released in the environment due to large scale industrial production but also reduces waste materials produced by small scale laboratories by promoting recycling. It aims to have a positive impact on upstream and downstream bioprocesses by enhancing effectiveness and reducing adverse consequences.
References
- Dave SR, Vaishnav AM, Upadhyay KH, et al. Microbial exopolysaccharide - an inevitable product for living beings and environment. J Bacterial Mycol Open Access. 2016;2(4):109-111. DOI: 10.15406/jbmoa.2016.02.00034
- Nwodo UU, Green E, Okoh AI. Bacterial exopolysaccharides: functionality and prospects. Int J Mol Sci. 2012 Oct 30;13(11):14002-15. Doi: 10.3390/ijms131114002. PMID: 23203046; PMCID: PMC3509562.
- Team, E. W. (n.d.). exopolysaccharide (CHEBI:72813). https://www.ebi.ac.uk/chebi/displayAutoXrefs.do?chebiId=CHEBI:72813
- Yamanaka, T., Yamane, K., Furukawa, T., Matsumoto-Mashimo, C., Sugimori, C., Nambu, T., Obata, N., Walker, C. B., Leung, K. P., & Fukushima, H. (2011). Comparison of the virulence of exopolysaccharide-producing Prevotella intermedia to exopolysaccharide non-producing periodontopathic organisms. BMC Infectious Diseases, 11(1). https://doi.org/10.1186/1471-2334-11-228
- Daegelen, P., Studier, F. W., Lenski, R. E., Cure, S., & Kim, J. F. (2009). Tracing Ancestors and Relatives of Escherichia coli B, and the Derivation of B Strains REL606 and BL21(DE3). Journal of Molecular Biology/Journal of Molecular Biology, 394(4), 634–643. https://doi.org/10.1016/j.jmb.2009.09.022
- Schembri, M. A., Dalsgaard, D., & Klemm, P. (2004). Capsule Shields the Function of Short Bacterial Adhesins. Journal of Bacteriology, 186(5), 1249–1257. https://doi.org/10.1128/jb.186.5.1249-1257.2004
- Flemming, H. C., & Wingender, J. (2010). The biofilm matrix. Nature reviews. Microbiology, 8(9), 623–633. https://doi.org/10.1038/nrmicro2415
- Paul, P., Nair, R., Mahajan, S., Gupta, U., Aalhate, M., Maji, I., & Singh, P. K. (2023). Traversing the diverse avenues of exopolysaccharides-based nanocarriers in the management of cancer. Carbohydrate Polymers, 312, 120821. https://doi.org/10.1016/j.carbpol.2023.120821
Authors
Deep Paralikar, Dr. Latika Shendre, Dr. Viniti Vaidya
Microbial Diversity Research Center,
Dr. D. Y. Patil Biotechnology and Bioinformatics Institute,
Dr. D. Y. Patil Vidyapeeth, Tathawade, Pune - 411033, Maharashtra, India.