Towards a Better Production of Bacterial Exopolysaccharides 2018

Applied Microbiology and Biotechnology (2018) 102:1587–1598 https://doi.org/10.1007/s00253-018-8745-7 MINI-REVIEW Towards a better production of bacterial exopolysaccharides by controlling genetic as well as physico-chemical parameters Dipanjan Sengupta1 & Sriparna Datta1 & Dipa Biswas1 Received: 9 September 2017 /Revised: 22 December 2017 /Accepted: 27 December 2017/Published online: 17 January 2018 # Springer-Verlag GmbH Germany, part of Springer Nature 2018 Abstract Bacterial extracellular polymeric substances, which are basically bacterial metabolites, have currently become a subject of great concern of modern day microbiologists and biotechnologists. Among these metabolites, bacterial exopolysaccharides or EPS, in particular, have gained a significant importance. EPS are formed by the bacteria in their late exponential or stationary phase of growth under special situations for specific purposes. They take part in the formation of bacterial biofilms. There is a great diversity in the types of EPS. Strikingly enough, a same species of bacterium can produce different types of EPS under different situations. The importance of EPS is largely because of their different applications in various industries. Now that the bacterial EPS has got the potentiality to become an upcoming tool in various futuristic applications of human benefit, the focus currently develops towards how better they can be produced in the laboratory by promoting the favorable factors for their production. While studying with different EPS forming bacteria, both the intrinsic factors like genetic configuration of the bacteria and the extrinsic factors like culture conditions under the influence of different physico-chemical parameters in order to maximize the EPS production have been taken into consideration. Both the factors have proved their worth. Hence, towards a better outcome for EPS production, it is indicated that a genetic manipulation of the bacteria should be synchronized with a proper selection of its culture condition by controlling different physico-chemical parameters. Keywords Exopolysaccharides (EPS) . Genetic manipulation . Culture conditions . Physico-chemical parameters . Quorum sensing Introduction 2015) because of their potential in commercial applications for human benefit (Freitas et al. 2011). In the last couple of decades, a good deal of enthusiasm has Unlike bacterial intracellular metabolites, which are not been noted in carrying out intensive studies in the field of only scarce but also difficult to isolate for detailed study, the applied microbiology and industrial biotechnology regarding extracellular metabolites, particularly the exopolysaccharide the discovery, isolation, characterization, and optimization of or EPS component of bacterial biofilms, have great potentials different bacterial extracellular polymeric substances, particu- in industrial applications for human welfare (Madhuri and larly the bacterial exopolysaccharides or EPS (Ruas-Madiedo Prabhakar 2014). Hence, different types of bacterial EPS have and de los Reyes-Gavilán 2005; Bramhachari and Dubey been isolated, characterized, and utilized in different domains 2006; Paulo et al. 2012; Bales et al. 2013; Torres-Rodríguez of human interest like food and beverage industry, preserva- et al. 2014; Madhuri and Prabhakar 2014; Liang and Wang tion of dairy products, cosmetics, textiles, agriculture, waste management, bioremediation, pharmaceuticals, medical ap- plication in wound healing, and so on (Ates 2015). Bacterial exopolysaccharides, as the name implies, are extracellular metabolites secreted by the organism especially in * Sriparna Datta [email protected] the late log (or exponential) phase or at the onset of stationary phase of growth when there is either a scarcity of further 1 nutritional and favorable factors or the organisms are unable Department of Chemical Technology, University of Calcutta, 92, to utilize them. EPS are high molecular weight biopolymers Acharya Prafulla Chandra Road, Kolkata 700009, India 1588 Appl Microbiol Biotechnol (2018) 102:1587–1598 and, though structurally diverse, they are essentially made up eventually resulting in a matrix-like network. This very much of a carbohydrate moiety and a non-carbohydrate moiety like mimics the cell adhesion molecule (CAM) in the eukaryotic pyruvate, acetate, succinate, and phosphate (Nwodo and Okoh cells. 2013). It is interesting to note that in biofilms, the microor- In reality, the isolation and characterization of bacterial ganism accounts for only about 10% of the dry mass EPS have not been very smooth because the yield of EPS from while the matrix accounts for the remaining 90% the bacteria is often very inadequate and is dependent on the (Flemming and Wingender 2010). Such extracellular nature of the culture media and on the concerned bacterial matrices impart several functions like microbial cell to species. Further, it is interesting to note that a particular bac- cell adhesion; microbial adhesion to a surface; signaling terial species can produce different types of EPS having dif- molecule for other cells to interact; inhibiting cellular ferent potentialities when the substrate of the culture media or desiccation; tolerating excessive changes in temperature, the culture condition changes (Dertli et al. 2013; Matsuyama pH, salinity, or radiation; fighting against antibiotics or et al. 2003). On the other hand, different species of bacteria toxic molecules; and even acting itself as a final source under the same genus can produce structurally different EPS of nutrition for the producer bacteria at extreme nutri- even if the culture condition remains unchanged (Celik et al. tional scarcity. 2008). Therefore, various attempts have been made to select Structurally, such metabolites are polymeric in nature and explore the capability of different species of a particular comprising repeating units which are, at large, polysac- bacterium having differences in its genetic configuration as charides in nature. Such extracellular polymeric sub- well as to study the role of different culture conditions under stances are henceforth coined as Exopolysaccharide or different physico-chemical parameters to optimize the yield of EPS. Apart from EPS, extracellular proteins are also a bacterial EPS so as to make such efforts economically viable produced as bacterial metabolites. The discovery of the and sustainable. first bacterial exopolysaccharide (EPS) dextran, pro- Eventually, it has come up to be a valid question whether duced by Leuconostoc mesenteroides, goes back to the the genetic composition of the bacterial species or the specific mid nineteenth century (Nwodo and Okoh 2013). It culture condition of the media plays a more distinctive or pioneered a field of an extensive research on the char- decisive role in the optimal production of a desired bacterial acter, structure, function, and potential applications of EPS. This review encompasses the significance and impor- bacterial EPS. tance of controlling both culture condition and bacterial genes With the advent of time, so many bacterial EPS like algi- on better EPS production in both qualitative and quantitative nate, cellulose, xanthan, gellan, levan, succinoglycan, and aspects. curdlan have been discovered, isolated, and studied in detail. They have diverse applications in human welfare like in food, oil, cosmetic, pharmaceutical, and other industrial sectors. For Why do bacteria produce EPS? example, bacterial EPS like dextran, levan, acetan, and xanthan have been widely used as viscosifier and thickening Owing to a gradual decline in natural resources, each agent in food industry; alginate has been established in wound and every life form on the Earth tends to exhibit a dual healing; colonic acid is widely used in cosmetic industry; trend for its survival. On one hand, during favorable emulsan has been identified for its propensity in the recovery conditions, there is a constant competition to outnumber of crude oil (Patel and Prajapati 2013); and so on. the other and, on the other hand, in adverse and ex- The isolation of EPS in the laboratory generally involves a treme situations, there is a tendency to colonize and stepwise procedure (Paulo et al. 2012). Sometimes this in- stay united to mitigate the hard time. volves a substantial time span for bacterial incubation such This dual behavior is well marked at bacterial level also. that the organism enters into the stationary phase of growth Based on such contrasting environmental conditions, they where the production of such secondary metabolites may be at synthesize several substances like toxins or endospores for its peak (Karuppiah et al. 2014). Often, the values of favorable sustenance and adaptation. Bacteria secrete polymeric sub- factors (like temperature, pH, and other culture conditions) for stance to their extracellular niche gradually resulting in the maximum production of bacterial metabolites differ signifi- formation of a colony of microbes often termed as biofilms cantly from those responsible for maximum growth of the or slime (Quiñones et al. 2005). Owing to the diversity of bacteria. This is really a matter of concern. Hence, intensive microbes, such metabolites produced have a diverse role in a research works are being contemplated to find out which fac- wide spectrum of research works and applications. tor(s) is/are primarily influencing the desired optimal yield of We often find that bio-films or pellicles are formed at the a bacterial EPS, whether it is primarily

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