Production and Roles of Biosurfactants and Bioemulsifiers in Accessing Hydrophobic Substrates

Abstract

Biosurfactants are one of the numerous adaptations of microorganisms metabolizing hydrocarbons and broadly represent a physiological response to specific requirements encountered by the cells depending on their environment. Some bacteria have developed the ''pseudosolubilization'' strategy to gain access to poorly soluble substrates and therefore produce highly dynamic low-molecular mass biosurfactants characterized by the capability to self-assembly in micelles, hemi-micelles or aggregates. Other bacteria interact with hydrocarbons directly by means of wall-bound biosurfactants that confer on the cell surface the appropriate hydrophobicity. High molecular mass bioemulsifiers in general adsorb tightly and cover the hydrocarbons thus dramatically increasing their apparent solubility. Although a variety of mechanisms and specializations distinguish biosurfactants, they all share a few essential traits. They are part of the process of interaction of microbial cells with surfaces as well as substrates. In addition to working on hydrocarbon solubilization they also act at the level of the cellular outer membrane allowing temporary and reversible modifications that control substrate access by the cells. As a consequence, a ''substrate effect'' can often be observed. Although the biosynthetic mechanisms for most remain unclear, substrates seem able to influence structural variations that make the biosurfactants particularly active towards the same substrate. Finally, many biosurfactants and their producing strains stimulate the growth of differently specialized bacteria which suggests that these molecules play a vital role in the interaction between the oil-degrading microbial communities and their environment.

Microbiotechnology Based Surfactants and Their Applications

“…The glycolipids (rhamnolipids, sophorolipids, trehalose lipids) consist of different sugars linked to β-hydroxy fatty acids while lipopeptides (surfactin, iturin, fengycin) consist of cycloheptapeptides with amino acids linked to fatty acids of different chain lengths. These molecules are amphiphilic in nature and this property allows them to dissolve in both polar and non-polar solvents (Perfumo et al, 2009;Smyth et al, 2010a,b). Biosurfactants are known for their excellent surface activity which involves lowering the surface and interfacial tension between different phases (liquid-air, liquidliquid, and liquid-solid); possessing a low critical micelle concentration (CMC) and formation of stable emulsions.…”

“…Biosurfactants produced in a growth associated manner (trehalose lipids) confer increased cell surface hydrophobicity on the producing organism. Cell surface hydrophobicity is essential for easy access and subsequent uptake of hydrophobic substrates by microbial cells (Perfumo et al, 2009;. These biomolecules are therefore suitable agents for different bioremediation technologies.…”

“…Bioemulsifiers are higher in molecular weight than biosurfactants as they are complex mixtures of heteropolysaccharides, lipopolysaccharides, lipoproteins and proteins (Perfumo et al, 2009;Sekhon-Randhawa, 2014). They are also known as high molecular weight biopolymers or exopolysaccharides.…”

“…These include, bioremediation (biodegradation), soil washing, biocontrol and spray application of fertilizers, enhanced oil recovery, de-emulsification, cosmetics, pharmaceuticals, antimicrobial agents, foods, beverages, etc. (Urum and Pekdemir, 2004;Perfumo et al, 2010;Rodrigues and Teixeira, 2010).…”

“…These include, bioremediation (biodegradation), soil washing, biocontrol and spray application of fertilizers, enhanced oil recovery, de-emulsification, cosmetics, pharmaceuticals, antimicrobial agents, foods, beverages, etc. (Urum and Pekdemir, 2004;Perfumo et al, 2010;Rodrigues and Teixeira, 2010).Although there has been an increasing number of reports describing the production and characterization of efficient biosurfactants, to date biosurfactants are still not able to economically compete with synthetic surfactants. This is mainly due to high production costs (Cameotra and Makkar, 1998;Deleu and Paquot, 2004).…”