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Biosurfactants are surface-active compounds produced by microorganisms. They display a variety of surface activities (surface tension decrease from 72 to 30 mN/m Helvaci et al., 2004) that increase the bioavailability of organic pollutants, including CO components, and thus enhance biodegradation (Nguyen et al., 2008; Rahman and Gakpe, 2008; Whang et al., 2008; Banat et al., 2010, 2014; Nguyen and Sabatini, 2011; Randhawa and Rahman, 2014). BSs belong to a structurally diverse group of amphiphilic biomolecules with both hydrophilic and hydrophobic moieties. They generally are grouped either as low or high molecular weight BSs, the former consisting of glycolipids and lipopeptides and the latter of high molecular weight polymeric BS. Due to their biodegradability and low toxicity they are very promising for use in remediation technologies as an alternative to the synthetic surfactants (Nguyen et al., 2008). Microbial BSs can replace the currently used chemical surfactants that are more toxic in many applications, like combating oil spills, bioremediation enhancement, micro-extraction of PAHs, pharmaceutical products, and detergent industry (Nguyen et al., 2008; Banat et al., 2010; Nguyen and Sabatini, 2011). There is a need for ecologically friendly and biodegradable surfactants (ionic or non-ionic) for reliable environmental cleanup. Commercially viable BSs have to be economically competitive therefore the development of good microbial BS producing cultures is required (Banat et al., 2000, 2010, 2014; Nguyen et al., 2008; Rahman and Gakpe, 2008; Whang et al., 2008; Nguyen and Sabatini, 2011; Randhawa and Rahman, 2014). Nowadays BSs still have not been employed extensively in industry because of the high production cost.
Biosurfactant production challenges and solutions for increasing the production yield are very well presented by Banat et al. (2014). Problems that limit BS industrial production include the required renewable substrate media quantities, slow growth rate of organisms on the substrate, low yield and final product purification from substrate impurities. Although cost effective BS production is still a goal to be attained, other important issues currently under investigation include the development-isolation of BS producing microorganisms (consortia or strains), the fine-tuning of their production ability by changing their incubation conditions (temperature, time, nutrients) and/or substrate type toward achieving a high yield and the production of lipid mixtures with an attractive/desired structure.
Sharma D. (2016) Classification and Properties of Biosurfactants. In: Biosurfactants in Food. SpringerBriefs in Food, Health, and Nutrition. Springer, Cham
S. Vijayakumar and V. Saravanan “Biosurfactants-Types, Sources and Applications” Review Article, 2015 “Types of biosurfactants: The chemically synthesized surfactants are usually classified according to their polarity, whereas, biosurfactants are generally categorized by their microbial origin and chemical composition as following.
Glycolipid: They are carbohydrates linked to long-chain aliphatic acids or hydroxyaliphatic acids by an ester group. Biosurfactants are majorly glycolipids. Among the glycolipids, the best known are rhamnolipids, trehalolipids and sophorolipids (Jarvis and Johnson, 1949). The sources and properties of the different glycolipids were discussed below:
- Rhamnolipids: Rhamnolipids are glycolipids, in which, one or two molecules of rhamnose are linked to one or two molecules of hydroxydecanoic acid. It is the widely studied biosurfactant which are the principal glycolipids produced by P. aeruginosa (Edwards and Hayashi, 1965)
- Trehalolipids: These are associated with most species of Mycobacterium, Nocardia and Corynebacterium. Trehalose lipids from Rhodococcus erythropolis and Arthrobacter spp. lowered the surface and interfacial tension in culture broth from 25-40 and 1-5 mNm, respectively (Asselineau and Asselineau, 1978)
- Sophorolipids: These are glycolipids which are produced by yeasts and consist of a dimeric carbohydrate sophorose linked to a long-chain hydroxyl fatty acid by glycosidic linkage. Sophorolipids, generally a mixture of at least six to nine different hydrophobic sophorolipids (Gautam and Tyagi, 2006) and lactone form of the sophorolipid is preferable for many applications (Hu and Ju, 2001)
Lipopeptides and lipoproteins: These consist of a lipid attached to a polypeptide chain (Rosenberg and Ron, 1999). Several biosurfactants have shown antimicrobial action against various bacteria, algae, fungi and viruses. Besson et al. (1976) reported the antifungal property and Singh and Cameotra (2004) reported the antibacterial property of the lipopeptide, iturin which was produced by Bacillus subtilis. Iturin from B. subtilis was found to be active even after autoclaving, pH 5-11 and with a shelf life of 6 months at -18°C (Nitschke and Pastore, 1990).
Surfactin: The cyclic lipopeptide surfactin are one of the most powerful biosurfactants composed of a seven amino-acid ring structure coupled to a fatty-acid chain via lactone linkage (Arima et al., 1968). Previous study reported that various physic-chemical properties of surfactin from B. subtilis. They found that the surfactin are able to reduce the surface tension and interfacial tension of water. The inactivation of herpes and retrovirus was also observed with surfactin.
Lichenysin: Bacillus licheniformis produces several biosurfacants which exhibit excellent stability under extreme temperature, pH and salt conditions which are similar to surfactin. McInerney et al. (1990) reported that lichenysin from B. licheniformis are able to reduce the surface tension and interfacial tension of water to 27 and 0.36 mN m-1, respectively.
Fatty acids, phospholipids and neutral lipids: Several bacteria and yeast produce large quantities of fatty acids and phospholipid surfactants during growth on n-alkanes. In Acinetobacter spp. 1-N, phosphatidyl ethanolamine-rich vesicles are produced which form optically clear micro-emulsions of alkanes in water. These biosurfactant are essential for medical applications. Gautam and Tyagi (2006) reported that the deficiency phospholipid protein complex is found to be the major cause for the respiration failure in the prematurely born children. They have also suggested that the isolation and cloning of the genes responsible for such surfactant can be employed in their fermentative production.
Polymeric biosurfactants: These are the best-studied polymeric biosurfactants including emulsan, liposan, alasan, lipomanan and other polysaccharide-protein complexes. Emulsan is an effective emisifying agent for hydrocarbons in water, even at a concentration as low as 0.001-0.01% (Hatha et al., 2007). Liposan is an extracellular water-soluble emulsifier synthesized by Candida lipolytica and is composed of 83% carbohydrate and17% protein (Cooper and Paddock, 1984; Chakrabarti, 2012). The application of such polymeric biosurfactant, liposan, as emulsifier in food and cosmetic industries were discussed by Chakrabarti (2012).”