1 Int.J.Curr.Biotechnol. Volume 5; Issue 12; December, 2017

Arun Kumar Pradhan, Environmental applications of biosurfactant: A critical review, Int.J.Curr.Biotechnol., 2017,5(12):1 - 9.

Environmental applications of biosurfactant: A critical review

Arun Kumar Pradhan 1, 2*

1Centre for Biotechnology, Siksha ‘O’ Anusandhan University, Bhubaneswar, Odisha, India - 751 0032M/S Odisha NET Academy & Research Centre, Bhubaneswar, Odisha, India - 751 021.

A R T I C L E I N F O A B S T R A C T

Article History:Received 01 November 2017Received in revised form 19 November 2017Accepted 12 December 2017Available online 30 December 2017

Key words:Bioremediation; Biosurfactants; Emulsi-fication; Poly-aromatic aromatic hydro-carbons; Surface tension.

Biosurfactants are macromolecules obtained from microorganisms belonging to several generaand phylum as secondary metabolites. These molecules have similar characteristics as ofsynthetic surfactants such lowering the surface tension, emulsification and dispersion,flocculation, cell aggregation, cell adhesion activity. The Biosurfactants vary in their chemicalproperties and molecular weight as well and are usually secreted extracellularly. The chemicalnature of biosurfactant varies from being fatty acids, phospholipids, and glycolipids tolipopeptides and is accordingly classified. Some of the examples of biosurfactant producingmicroorganisms are Lysinibacillus fusiformis, Bacillus tequilensis, Acinetobacter sp., Aspergillusniger, Arthrobacter. The enormous diversity of biosurfactants obtained from various organisms,a wide range of applications is possible. Polyaromatic aromatic hydrocarbons are by productsduring petroleum refining and other industrial process. These have oncogenic characteristicsand are difficult to degrade to the presence of large number of aromatic rings since the ringshelps in decreasing the volatility and solubility. Biosurfactants enhance the mineralization ofthese poly-aromatic hydrocarbons by direct adhesion of cell on PAH and thus emulsifying it.Considering several benefits of microbial biosurfactants on reducing the environmental pollutionand enhancing the yield of industrial process, the biosurfactants have promising future to beused in industries. Several microbial biomes need to be exploited for novel biosurfactants andshould be applied for the benefit and a sustainable environment.

IntroductionMicrobial population metabolise a wide range of bioactivecompounds habitually on surface of cell or secreteoutside the cell. These secondary metabolites are havingsurfactant like properties is called bio­surfactants.Biosurfactants are secondary metabolites havingamphipathic characteristics. This characteristic propertycomes from the presence of a polar head and non-polartail. These are obtained from diverse bacterial, fungusand plants. The diversity of sources itself describes thediverse structure correlated to functionality. The synergyof the hydrophobic tail is parallel across the microbialdomain. The chemical structure of biosurfactants mostlyincludes either a glycan bonded to a lipid molecule or afatty acid attached to a peptide or it may happen that achain of amino acids linked to lipid molecule which inturn attached to a polysaccharide (Pradhan et.al, 2013 &2015). Biosurfactants are categorised into different groupsbased on their chemical nature (Table 1). The utilizationof biosurfactants is considered to be an alternative tothose of commercially available surfactants. Due to theirimmense diversity in chemical structure, thebiosurfactants exhibit different metal specificity and thusgiving a view of its efficiency for removal of toxic metals.The use of biosurfactants has many advantages such aseconomic start up, less expensive for large scaleprocessing, environmental friendly and overall can

considered as a green technology. Microbial surfactantsare of biotechnological importance and exhibit hugepotential such as: lowering of surface tension, spreading,enhancing the growth of microorganisms, metalsequestration, inducing apoptosis in cancerous cells andantimicrobial action (Pradhan et.al, 2013, 2014).

Advantages of biosurfactantsThe unique properties of biosurfactant such asbiodegradability, widespread applicability, highpotentiality for pharmaceuticals strays it from syntheticsurfactants. Its biotechnology has proved it as animportant discovery for replacement of chemicalsynthetic surfactant.

Few merits of biosurfactants as compared to chemicallysynthesized surfactants are listed below-Biodegradability: They are easily biodegradable ascompare to the chemical surfactant.Biocompatibility and digestibility: These propertiesallow their application in cosmetics, pharmaceuticals andfood ingredients.Specificity: Biosurfactant are more specific in action, asthese have specific organic functional groups whichimpart more variability in structure and function ofmolecule.Bioremediation: Biosurfactants are efficient in degradingindustrial emulsions, degradation of oil spillage,solubilising toxic metals in polluted soil.Easy availability of microbes and feed stock:Biosurfactant producing microorganism can be isolated

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*Corresponding author.Email address: arunpradhan83@gmail.com

ISSN: 2321 - 8371

Volume 5; Issue 12; December, 2017 Int.J.Curr.Biotechnol. 2

from many pristine as well as polluted ecosystems likenatural water bodies and soil besides waste like oil/hydrocarbon contaminated soil, or municipal waste. Theraw materials require for production of biosurfactant arealso easily available

Types of biosurfactantsThere are different types of biosurfactants found innature and are classified into two different categoriesbased on chemical structure of the biosurfactant molecule.Though not all are widely understood, but are stillimportant for green chemistry. Below mentioned aredifferent types of biosurfactants with brief descriptions:

GlycolipidsA glycolipid is defined as sugar moiety attached to achain of n- numbers of aliphatic acids through an esterbond. The glycan parts are mostly mono- or di-hexosesattached lipid moieties. Commonly rhamnose areobserved to be present in the biosurfactants producedby the Pseudomonas genera.

RhamnolipidsRhamnolipid is probably the most studied biosurfactantsamongst the all. The mono-rhamnolipid from P.aeruginosa grown on hydrocarbons (2-O-á-L-r ha mn opyr an osyl-á-L-3 -hydr oxydecan oyl -3 -hydroxydecanoic acid) and (2-O-á-1, 2-L-r h a m n op yr a n osyl -á - L- r h a m n op yr a n osyl -â -hydroxydecanoyl-â-hydroxydecanoate) was observed tobe di-rhamnolipid (Figure 1) (Edwards and Hayashi, 1965)

Sophorolipids SophorolipidsYeasts like in particular Candida (Torulopsis) bombicola,(Noordman et al., 1998; Salihu, Abdulkadir andAlmustapha, 2009) secretes exo-glycolipids known assophorosides consisting a dimer of sophorose joinedto fatty acid which exhibits more potency as detergents(Figure 2).

Trehalose lipidsThis is a lipid present in cell wall of Mycobacteriumtuberculosis (Figure 3). It is basically observed to betrehalose dimycolate responsible for the virulency ofMycobacterium tuberculosis and confers appreciableresistance against anti-tubercular drugs.

Cellobiose lipidsThis is a lipid consisting of ustilagic acid (Figure 4) linkedwith cellobiose secreted by Ustilago maydis (Noordmanet al., 1998; Salihu, Abdulkadir and Almustapha, 2009)

LipopeptidesThis is the type of biosurfactant which contains bothlipid and protein parts (mainly oligopeptide). Some ofthe well studied examples include surfactin, arthrofacin,iturin, serrawetin W2 etc. (Priya and Usharani 2009; Tanget al. 2010; Liu et al. 2012).

SurFactinSurfactin is a most common biosurfactants mainlyproduced by Bacillus spp .(Deka and Das, 2009;Gandhimathi et al., 2009). In surfactin peptide moietyremains in cyclic form (Priya and Usharani, 2009; Tang etal., 2010; Liu et al., 2012). There are 7 amino acidsattached to carboxyl and hydroxyl groups of a 14-C acidwith a lactone ring (Figure 5). It is having variousapplications like recovery of oil, bioremediation soil(Mulligan, Yong and Gibbs, 1999), antifungal activity (Liuet al., 2012), antibacterial property, and cytotoxic effects.

ArthrofactinMorikawa et.al. isolated a bacterium Arthrobacter speciesstrain MIS38,that produces lipopetide type biosurfactantsnamed as arthrofactin (Figure 6). They characterized thisbiosurfactant as 3-hydroxydecanoyl-D-leu-D-asp-D-thr-D-leu-D-leu-D-ser-L-leu-D-ser-L-ile-L-ile-L-asp lactonewith the help of NMR, GC-MS and HPLC.(Morikawa etal., 1993).

Bacillus subtilis CMB32 produces iturin-A (Figure 7)which controls a fungal pathogen Colletotrichumgloeosporioides, causal agent of anthracnose diseaseof pepper, blueberry, mango, and other crops (Peypouxet al., 1978; Kim et al., 2010).

Serrawettin W2Serratia marcescens W2 produces a biosurfactant namedas serrawettin (Figure 8). The production is regulated byacyl homoserine lactone (AHL) (Yue Chan et al., 2013).

Fatty acidsA number of microorganisms produce fatty acids whenthey are growing on polycyclic aromatic hydrocarbons.Gautam and Tyagi reported that N-phosphatidylethanolamine producedby Acinetobacterspp. was able to emulsify alkanes dissolved in water.The length of aliphatic chain of fatty acid determined thehydrophilicity and lipophilicity of biosurfactant. (Gautamand Tyagi 2006).

Polymeric biosurfactantsMost of the polymeric biosurfactants’ structure andfunctions are well studied.These include emulsan,liposan, alasan, lipomanan etc. According to Hatha et al.a very low concentration (0.001- 0.01%) of emulsansemulsify hydrocarbons in water (Hatha et al., 2007).Candida lipolytica also produces polymericbiosurfactants like liposan (Cooper and Paddock, 1984).A potent extracellular polyanionic amphipathicheteropolysaccharide is produced by Acinetobactercalcoaceticus RAG-1 and acts as efficient emulsifier(Rosenberg et al 1979).

Applications of biosurfactantA number of environmental applications are seen bybiosurfactants (Figure 9).

Restoration of water bodies from oil spillagePetroleum industry is one of the best non-renewableenergy resources for major transportation systems in acountry. However, they are also equally majorenvironmental pollutants. Spillage of petroleum productsinto the water bodies not only contaminates the watersystem but also brings toxicity to a major population oforganisms living in water bodies. Previewing this, a lotof attention has been paid to remediate such oil spillageaccidents and following it innovative techniques andtechnologies are being implemented. Application ofbiosurfactants is one such innovative technology toremediate the oil spillage.

A major accident that took place in 2011, November(Sedco 706 oil rig, Brazil) causing a leakage of total of5943 L spreading over 163 km2. Yet another oil spillagethat took place in the Gulf of Mexico in 2010 caused bythe explosion of an oil rig in USA. Numerous accidentshave been evident for oil spillage and have beenremediated using biosurfactants. The biosurfactant actson the oil particles causing distortion ofmolecules(emulsification) thus leading to breakdown ofoil. A novel approach which uses Pseudomonas putida

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5 Int.J.Curr.Biotechnol. Volume 5; Issue 12; December, 2017

Figure 1: Structure of (a) mono-rhamnolipid and (b)di-rhamnolipid

Figure 2: Sophorolipid

Figure 3: Trehalose lipid Figure 4: Cellobiose lipids (n=2-4, R=H/OH)

Figure 5: Structure of surfactin

Figure 6: Structure of arthrofactin

Figure 7: Structure of iturin

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Figure 8: Structure of serrawettin

Figure 9: Graphical representation for environmental applications of biosurfactant

commonly recognized as superbug was found to besuitable for restoration of water bodies from oil spillageand continues to one of the best findings till date (Zhanget al., 2005).An oil spill occurs when petroleum crude orprocessed is accidentally released into the environmentthereby spoiling the nearby aquatic ecosystem. Duringoil spillage, oil floats and makes the survivility of aquaticorganisms impossible. So research is required to find outthe organisms which can degrade oil, biosurfactantproducing bacteria.

A number of poly aromatic hydrocarbon degradingbacteria are discovered for example: Pseudomonasaeruginosa, Pseudomonas fluorescens, Bacillus spp.,Mycobacterium spp., Rhodococcus spp., Haemophilusspp., (Haritash and Kaushik, 2009). Bordoloi and Konwar,2009 described that different Pseudomonas aeruginosastrains enhances solubility and metabolism of petroleumhydrocarbons like phenanthrene, pyrene, fluorine andcrude oils.

Microbial Enhanced Oil Recovery (MEOR)There are many existing oil recovery methods areavailable like chemical flooding, miscible CO2 injection,and thermally enhanced oil recovery methods. But thisis one of the most important method for reusing the non-renewable source of energy. It is economic and a greentechnology to recover the residual oil present inreservoirs. The underlying principle of MEOR relies onthe crude oil’s viscosity reducing capacity of potentialmicroorganisms. Few of the methods used earlier wereinjection, dispersion and propagation of the potentmicroorganisms from the residual oil reservoirs, thenspecifically degrading of oil components followed by theexecuting the effect of microbial metabolites on the oilparticles. Fossil fuels are probably will remain the bestsource of energy despite the high economics ascompared to other renewable energy sources. Accordingto Cosse R. (1993) around 30-40% of oil is contributed byprimary methods whereas 15-25 % by secondary methods

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and rest (2–4 trillion barrels) is by microbial enhanced oilrecovery. This can be carried out by altering the physico-chemical properties of reservoirs and the environmentfor microbial growth.

Hydrocarbon degradation from waste resourcesPolycyclic aromatic hydrocarbons are a category of morethan chemicals that are insoluble and released into airfrom burning of hydrocarbons. These are persistentorganic pollutants (POPs). Alasan is a type of anionicalanine-containing bio-emulsifier. Since the polycyclicaromatic hydrocarbons are not soluble compounds. It isstudied the effect of alasan to increase the efficiency ofsolvents to solubilize the PAHs. From his report, it wasevident that the alasan concentration was linear with thesolubilisation of PAHYs. It was suggested that thebioemulsifier solubilizes PAHs by physical interaction,because of its hydrophobic nature (Barkay et al., 1999).Different biosurfactants produced from different sourceshave been reported for the hydrocarbon degradation(Table 2).

Protecting municipal water systems from mosquitolarvaeMosquitoes are one of the deadliest vectors causing alarge mortality (WHO reports 500 million) throughout theworld (Nabar & Lokegaonkar, 2015). The increase in thepopulation density has become more prone to themosquitoes due to increased rate of municipal wastescaused by people. Chemical industries are in urge toproduce more of chemical mosquitocides and theincreased resistivity of mosquitoes has brought seriousconcerns in the scientific community. Microbialmosquitocides can be considered as alternative to thechemical ones. Thus microbial insecticides can beconsidered as alternatives to chemical insecticides. Astudy by Nabar & Lokegaonkar (2015) reported thatbacteria producing larvicidal metabolites from variousenvironments are highly effective. The tested againstlarvae of Culex and Aedes moquitoes and found that 100% mortality of the mosquito larvae caused at very lowconcentration of secondary metabolites. Microbialmetabolites are highly capable due their selective toxicityand ready decomposability and are economic friendly.The high utility of biosurfactants against mosquito larvaemay be due to surface tension reducing capacity whichforces larvae sink into the water and thus death occurs.

Biobeneficiation of heavy metalsNickel is an important element for industrial purposes.Extraction of Ni from waste resources is extremelyimportant. Surfactants have proved to be important forextraction of Ni in the recent past. It is reported that theeffect of surfactant Tween-20 on the nickel extraction.Chromite over burden sample was used for Ni leaching.The bioleaching was carried out in presence ofAspergillus niger. The surfactant was also tested for itseffect on the growth of the same fungus. They observedthat the consumption of sugar in presence of thesurfactant increased so as the leaching efficiency (Beheraet.al, 2012).Similar studies have also been performed forthe recovery of industrially important metals such as Cuand Pb. Juwarkar et al. (2008) studied the enhancingcapacity of rhamnolipid for the recovery Cd, Cr, Pb, Cu,Ni.

Reduction of ChromiumChromium is the 7th most rich element on earth and can befound in 9 different oxidation states. Amongst the mostcommon are the Cr (III) and Cr (VI) in nature. Cr (VI)isconsidered to be carcinogenic and is considered as an

environmental hazard and on other side Cr (III) is requiredto animals as nutrition (USEPA, 1995). The difference onpart of both the states of Cr is due to their solubility. Athorough study on the detoxification of Cr (VI) in presenceof negatively charged biosurfactant was carried out byMassara et.al. (2007). They reported that thebiosurfactants could enhance the removal of Cr fromkaolinite was significant. They also studied it by using 2factorial experiments. Over a period of 24 days, near about100 % Cr was reduced which significantly suggested thatrhamnolipids are of beneficial use (Massara et.al, 2007).

ConclusionMicrobial biosurfactants are one of the importantsecondary metabolites. The biosurfactants have hugepotential in preventing and restoring the environment.The enormity in diversity of microorganisms producingbiosurfactants is incomparable to other sources. The widevariety of applications owes to the varied chemicalstructure of different biosurfactants of microbial origin.Some of well-studied biosurfactants are rhamnolipid,surfactin, elasting, emulsan etc. Due to the role andassociation of different macromolecules into one formgive biosurfactants the ability decontaminate municipalwater systems, reducing the carcinogenic hexavalentchromium, reduction or oxidation of heavy metals forbeneficiation. On the basis of its potentiality, themicrobial biosurfactants certainly are the need of the hourto protect our environment.

AcknowledgementThe author shows gratitude to Siksha ‘O’ AnusandhanUniversity, Bhubaneswar and M/S Odisha NET Academy& Research Centre, Bhubaneswar, Odisha for providingscientific support.

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