Nazim F. Islam and Hemen Sarma
Department of Botany, N N Saikia College, Titabar, Assam, India
CHAPTER MENU
2 2.2 Metagenomics Application: A State-of-the-Art Technique
3 2.3 Hydrocarbon-Degrading Bacteria and Genes
4 2.4 Metagenomic Approaches in the Selection of Biosurfactant-Producing Microbes
5 2.5 Metagenomics with Stable Isotope Probe (SIP) Techniques
6 2.6 Screening Methods to Identify Features of Biosurfactants
7 2.7 Functional Metagenomics: Challenge and Opportunities 2.7.1 Single vs Multiple Host Expression System 2.7.2 Metagenomic Clone Libraries
10 References
2.1 Introduction
Humans have been using soap and soap‐like substances for thousands of years. The development of soap‐like materials is evident in ancient Babylon about 2800 BCE [1]. In India, reetha or soapnut (Sapindus mukorossi Gaertn.) has traditionally been used as a hair cleanser, among other things. Today, soap comprises a half of the total global production of surfactants, which is projected to be 15 mt/y. Linear alkylbenzene sulfonate (LABS) (1700 kt/y), lignin sulfonate (600 kt/y), fatty alcohol ethoxylates (700 kt/y), and alkylphenol ethoxylates (500 kt/y) are particularly widely produced surfactants [2]. Surfactants are hydrophobic and hydrophilic molecules capable of altering surface/interface tension and improving the solubility of polar compounds in non‐polar solvents [3]. Similarly, biosurfactants are amphiphilic metabolites derived from microorganisms. These are interesting alternatives to conventional chemical surfactants because they are easily degradable in the environment. Hydrophilic moieties of biosurfactant molecules are mainly carbohydrates, carboxylic acids, phosphates, amino acids, cyclic peptides, or alcohols, whereas hydrophobic moieties are fatty acids, hydroxy fatty acids, and alkyl and β‐hydroxy fatty acids [4]. Natural as well as synthetic surfactants, which are widely used in industrial processes, have various properties; therefore, they are used as solvents, stabilizers, lubricants, and foaming agents. Biosurfactants are produced by different strains of bacteria, fungi, and yeast in natural environments. These multifunctional microorganism‐derived biomolecules have been extensively studied and reported in scientific literature [3, 5].
Biosurfactants are generally classified into a low or a high molecular weight group based on their chemical nature. Low molecular weight surfactants are widely used to lower surface‐to‐surface stress, while high molecular weight surfactants are generally used as emulsifiers and stabilizers [6]. For details of the composition, classification, critical concentration of micellization (CMC) values and properties of biosurfactants, see Chapter 1.
Microbe‐derived surfactants appear to display a performance similar to synthetic surfactants [7]. While synthetic surfactants are commercially preferred during industrial applications, their use leads to the development of undesirable environmental pollutants [5, 8]. The majority of synthetic surfactants such as linear alkylbenzene sulfonate (LABS) are non‐biodegradable with adverse environmental effects. Contrary to these, biosurfactants are less persistent and biodegradable in the environment owing to their biological origins [9]. In addition, most biosurfactants are active in a wide range of temperatures, pH and other environmental conditions [10].
Microbiologically derived surfactants have been widely used in industries such as emulsifiers, dispersants, foaming agents, and wetting agents [11], with a lower CMC value, which improve their performance over synthetic surfactants [12]. Some common sustainable applications of biosurfactants in the environment and in biomedicine (bioremediation, medical technology, food processing and pharmaceutical formulations, and cosmetics) are discussed in more detail in Chapters 5, 10, 11, and 19.
Many microorganisms, which are potential producers of biosurfactants, inhabit oil‐contaminated soil in and around oil fields. One of the major hindrances for the discovery of novel biosurfactant‐producing strains is the isolation and cultivation of biosurfactant‐producing microbes. The metagenomics approach allows for the extraction of DNA (eDNA) from the environmental DNA pool and the screening for biosurfactant‐producing genes [13]. The aim of this review is therefore to discuss the possibility of oil field soil being a repository for bacteria‐producing biosurfactants that help in the desorption of oil during microbial degradation, their isolation, and screening techniques. This could be of enormous scope for industrial application and bioremediation. In addition, this article discusses current developments in the research on molecular techniques such as metagenomics combined with a stable isotope probe (SIP) for the discovery of new microbial strains that produce biosurfactants.
2.2 Metagenomics Application: A State‐of‐the‐Art Technique
Most metagenomic studies have focused mainly on screening environmental DNA samples that produce novel biomolecules and on the diversity of microbes in different environments [14]. Metagenomics offers multiple uses and does not have an exhaustive list of applications. This technique has been used successfully to discover novel genes and microbes (for biodegradation and bioremediation), investigate microbial diversity, discover medicines, identify enzymes, monitor pollutions, and so on (Figure 2.1).
Figure 2.1 Application of the metagenomic technique for environmental management of advanced biomedical applications.
Techniques of metagenomics may also be used to classify genes/microbes from environmental samples that produce biomolecules. These multifunctional, fascinating biomolecules with diverse structural complexities can be used in a number of advanced environmental and bio‐science applications [15].
In
