**Biosurfactants as Useful Tools in Bioremediation**

Claudia Isabel Sáenz-Marta, María de Lourdes Ballinas-Casarrubias, Blanca E. Rivera-Chavira and Guadalupe Virginia Nevárez-Moorillón

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/60751

#### **Abstract**

Environmental pollution by organic contaminants is a major problem today because it has affected many environments. Hydrophobic contaminants are of special concern since their molecules can be bound to the soil particles, but because of its low solubility in water and high interfacial tension, those contaminants cannot be easily removed. To help with desorption of contaminants, surfactants can be used in soil and water remediation technologies. Amphiphiles that can form micelles are termed as surface active agents or *surfactants* and are among the most commonly used chemicals in everyday life. Chemically produced surfactants have increasingly been replaced by biotechnology-based products, obtained either by enzymatic or microbial synthesis, because they can be produced using natural resources. The group of surface active biomolecules produced by living organism is called *biosurfactants*. Originally, biosurfactants attracted attention as hydrocarbon-dissolving agents in the late 1960s and as potential replacements for synthetic surfactants (carboxylates, sulfonates and sulfate acid esters) in the food, pharmaceutical, and oil industries. Synthetic surfac‐ tants currently used are usually toxic and hardly degraded and as such are also a contaminant in the environment. To replace synthetic surfactants, biosurfactant production needs to be cost-effective; therefore, it is important to develop culture conditions with low-cost materials using efficient biosurfactant-producing microbial strains. Although bacteria have been extensively studied for biosurfactant production, yeasts are also potential biosurfactant-producing microorganisms. Because of their unique structures, biosurfactants may have a greater range of properties that can be

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exploited commercially. This review article will describe microorganisms related to biosurfactant production, including yeasts, as well as their role in bioremediation.

**Keywords:** Biosurfactant, soil yeast, microbial communities in soil, bioremediation

## **1. Introduction**

Recently, there are many reports of soil and surface water locations that are contaminated with organic pollutants, with a great impact on soil and groundwater. Because of its low solubility in water and high interfacial tension, those contaminants cannot be easily removed. Bioreme‐ diation has become one of the methods used in the remediation of contaminated sites; bioremediation strategies are based on the use of different microorganisms: bacteria, yeasts, or fungi isolated from soil or from a place where there is a presence of contaminants such as hydrocarbons, which facilitate the cleaning of the contaminated sites. Bioremediation studies begin with the isolation and identification of microorganisms from soil and water that are able to degrade these contaminants. Some hydrocarbon-degrading microorganisms are also able to produce biosurfactants. Biosurfactants produced by the microorganisms in the environment help them to take the hydrocarbons as carbon source, either by making available the hydro‐ carbon by releasing biosurfactant into the environment or by changing its cell surface so that the contaminant can be absorbed.

Originally, biosurfactants attracted attention as hydrocarbon dissolving agents in the late 1960s as potential replacements for synthetic surfactants (carboxylates, sulfonates, and sulfate acid esters), especially in the food, pharmaceutical, and oil industries. Synthetic surfactants currently used are usually toxic and hardly degraded by microorganism, causing damage to the environment. Most of the biosurfactants are high molecular weight lipid complexes, which are normally produced under aerobic conditions. The classification of biosurfactants is based on their chemical composition, their mode of action, and the microorganisms that produce it. Biosurfactants can be of high or low molecular weight, and based on their composition, they can be glycolipids, phospholipids, lipopeptides, or a mixture of amphiphilic polysaccharides, proteins, lipoproteins, or lipopolysaccharides. Microorganisms also produce surfactants that are in some cases a combination of many chemical types referred to as the *polymeric microbial surfactants*. Because of their unique structures, biosurfactants may have a large range of properties that can be exploited commercially.

Regarding their mechanism of action, some compounds are better at decreasing the surface tension (biosurfactants), and others are able to produce stable emulsions (bioemulsifiers). Best known biosurfactants are produced by bacteria, and there are many studies on them, especially on *Pseudomonas* spp., strains that produce rhamnolipids. However, it is necessary to find new types of biosurfactants and bioemulsifiers, and the studies of other organisms are increasing recently. Yeast and fungi have demonstrated to produce biosurfactant and bioemulsifiers with very good results. The aim of this chapter is to describe microbial biosurfactant, especially those produced by yeasts and to propose their use in bioremediation.
