Biosurfactants And Its Application

Project and Seminar Material for Microbiology

Abstract

This study was carried out on the application of biosurfactant. Microbial surfactants (Biosurfactants) are amphiphilic compounds produced in living spaces or excreted extracellular hydrophobic and hydrophilic moieties that confer on the organism the ability to accumulate between fluid phases thus reducing surface and interfacial tension. Biosurfactants are produced by several microorganisms which include Acinetobacter sp., Bacillus sp, Candida antartica, Pseudomonas aeruginosa. The physiological role of biosurfactant production in microorganisms includes antimicrobial activity and the ability to make substrates readily available for uptake by the cells in adverse environmental conditions. Biosurfactant are classified based on their molecular weight and chemical composition. Some advantages of biosurfactants are biodegradability, low toxicity, better surface and interfacial activity while some of its limitations are inability to scale up the production process and patent rights. Factors influencing biosurfactants production are the nature of the carbon source, nitrogen source, the C:N Ratio, temperature, aeration and pH. Biosurfactants have several applications in agriculture, industry, medicine and the petroleum sectors.

Chapter One

Introduction

1.1 Background of the Study

Biosurfactants are surface active agents or amphiphilic compounds which can reduce surface and interfacial tensions of liquids. Biosurfactants produced mostly by microbial cells are excreted extracellularly and contain hydrophobic/lipophilic and hydrophilic moieties that reduce surface tension. However, for degradation of crude oil- contaminated site, special microbial cultures are needed which can survive in the contaminated environment and degrade the contaminant efficiently and completely. This can be enhanced by bioremediation techniques which include aeration of the contaminated site and nutrient additions, supplementing the source of microorganisms capable of degrading the contaminant (bioaugmentation) and the enhancement of the desorption of pollutants from particulates using biosurfactants which increase hydrocarbon degradation (Christofi and Ivshina, 2002). Surface tension is defined as the free surface enthalpy per unit area (OECD, 1995) and is the force acting on the surface of a liquid leading to minimization of the area of that surface (Christofi and Ivshina, 2002). Surfactants do this, by accumulating at the interface of immiscible fluids thereby increasing the solubility, mobility, bioavailability and subsequent biodegradation of hydrophobic or insoluble organic compounds (Rahman et al., 2003; Singh et al., 2006).

Surfactants are amphiphilic compounds that reduce the free energy of the system by replacing the bulk molecules of higher energy at an interface (Mulligan et al., 2001; Mulligan, 2005). They contain a hydrophobic portion with little affinity for the bulk medium and a hydrophilic group that is attracted to the bulk medium. They are used industrially as adhesive, flocculating, wetting and foaming agents, de-emulsifiers and penetrants (Mulligan, 2005). The effectiveness of a surfactant is determined by its ability to lower surface tension, which is a measure of the surface free energy per unit area required to bring a molecule from the bulk phase to the surface. These surfactants can be synthetic or naturally produced by microorganisms, hence the name biosurfactants.

Biosurfactants are surfactants that are produced extracellularly or as part of the cell membrane by bacteria, yeasts and fungi (Karanth et al., 1999, Mulligan 2005, Tabatabaee et al., 2005). They are a structurally diverse group of surface-active molecules synthesized by microorganisms. These molecules reduce surface and interfacial tension in both aqueous solutions and hydrocarbon mixtures, which makes them potential candidates for enhancing oil recovery and deemulsification processes (Desai and Banat, 1997; Youssef et al., 2004; Muthusamy et al., 2008). They are amphipathic molecules enabling the formation of specialized structures vital to their action. They function by residing at the oil-water interface (Christofi and Ivshina, 2002).

Biosurfactants lower the interfacial tension between immiscible fluids enabling them to be miscible through the creation of additional surfaces. A single interface consisting of an immiscible and miscible constituent is transformed into smaller interface of the two constituents (Christofi and Ivshina, 2002). They improve the bioavailability of hydrocarbons to the microbial cells by increasing the area at the aqueous-hydrocarbon interface. This increases the rate of hydrocarbon dissolution and their utilization by microorganism (Tuleva et al., 2001). The main physiological role of biosurfactants is to permit microorganisms to grow on water immiscible substrates by reducing the surface tension at the phase boundary, thus making the substrate more readily available for uptake and metabolism (Thambivajah, 1998).Therefore, the use of biosurfactant should be a promising means to emulsify polluted oils prior to biodegradation (Maneerat and Pheetrong, 2007).

Petroleum bioremediation is carried out by microorganisms capable of utilizing hydrocarbons as a source of energy and carbon. These microorganisms are ubiquitous in nature and are capable of degrading the various types of hydrocarbons – short-chain, long chain and numerous aromatic hydrocarbons. All these compounds have low solubility in water. This fact, coupled to the fact that the first step in hydrocarbon degradation involves a membrane-bound oxygenase, makes it essential for bacteria to come in direct contact with the hydrocarbon substrates (Ron and Rosenberg, 2002). One biological strategy that can enhance contact between bacteria and water-insoluble hydrocarbons is emulsification of the hydrocarbon. Therefore, it is not surprising that bacteria growing on petroleum usually produce potent emulsifiers. These surfactants help to disperse the oil, increase the surface area for growth, and help detach the bacteria from the oil droplets after the utilizable hydrocarbon has been depleted (Rosenberg, 1993; Ron and Rosenberg, 2002). Biosurfactants generally increase the adhesion of cells to the substrate (Calvo et al., 2004).

1.2 Objectives of the Study

The main objective of the study is to carryout an overview of biosurfactant and examine its application. The following are the specific objectives of the study:

The application of biosurfactants in the Petroleum Industry.
The application of biosurfactants in the Food Industry.
The application of biosurfactants in the Cosmetic Industry.
Therapeutic and Biomedical application of biosurfactant.
The application of biosurfactants in the Pharmaceutical Industry.

1.3 Rationale of the Study

The cost of biosurfactant production is relatively high due to the source of nitrogen compound used in its production. To produce biosurfactants economically, increased yields are necessary. This study was aimed at exploring the application of biosurfactants.

Chapter Three

Conclusion

Biosurfactants are amphiphilic compounds produced in living surfaces, mostlyon microbial cell surfaces or excreted extracellular hydrophobic and hydrophilic moieties that confer the ability to accumulate between fluid phases, thus reducing surface and interfacial tension at the surface and interface respectively.

During the recent years there is an increasing environmental awareness and therefore, it might be reasonable to assume that microbial surfactants have a promising role to play in the years to come. Considering the importance of biosurfactants, there is an urgent need to gain a greater understanding of the physiology, genetics and biochemistry of biosurfactantproducing strains and to improve the process technology to reduce production costs for commercial level production of biosurfactants. Therefore, an extensive cooperation among different science disciplines is needed in order to fully characterize the biochemical properties of biosurfactant and exploration of their potential applications in different industrial sectors. Compared with chemical surfactants, the biosurfactants have the advantage of biodegradability and lower toxicity that make them more appropriate for replacing chemicals. There are several types of biosurfactants in market but no single biosurfactant is suitable for all potential applications. Chemically synthesized compounds are cheaper than the biosurfactants available in the market basically because biosurfactants have their high production costs and the lack in comprehensive toxicity testing. The cost of production of biosurfactants may be significantly reduced for selected applications such as using sterilized or pasteurized fermentation broth without any need for extraction, concentration or purification. The crude product may be used by oil industries and environmental bioremediation in many applications. Strategies like medium and downstream process-optimization may also have a positive impact on cost reduction. It is very alarming that large chemical companies seem not to be interested in research in these areas.

The usefulness of biosurfactants in bioremediation is however expected to gain more importance in the coming years. Their success in bioremediation will require precise targeting to the physical conditions and chemical nature of the pollutant affected areas. Encouraging results have been obtained for the use of biosurfactants in hydrocarbon pollution control in marine biotopes in closed systems (oil storage tanks) and, although many laboratory studies indicate potential for use in open environments, a lot remains to be demonstrated in pollution treatment in marine environments or coastal areas.

Lipases had been used for the enzymatic synthesis of manmade surfactants and have given a whole new dimension to biosurfactant production. With increased efforts on developing improved application technologies, strain improvement and production processes, biosurfactants are expected to be among the most used and produced chemicals in the near future.