Biosurfactants and bioemulsifiers from marine sources

Abstract

Marine microbes are known for their many novel extra- and intracellular products such as antibiotics, enzymes, biopolymers, pigments, and toxins. Reports suggest that so far more than 10,000 metabolites with broad-spectrum biological activities and interesting medicinal properties have been isolated from marine microbes (Kelecom, 2002). However, due to the enormity of the marine biosphere, most of the marine microbial worlds remain unexplored. It has been estimated that <0.1% of marine microbial world has been explored or investigated (Ramaiah, 2005). Among various marine bioactive compounds, microbial biosurfactants (BSs) are of great importance due to their structural and functional diversity and industrial applications (Banat et al., 1991; Banat, 1995a,b; Rodrigues et al., 2006a). Marine microbial BSs are such metabolites with many interesting properties. BSs are basically amphiphilic surface active agents produced by bacteria, fungi, and actinomycetes. They belong to various classes including glycolipids, glycolipoproteins, glycopeptides, lipopeptides, lipoproteins, fatty acids, phospholipids, neutral lipids, lipopolysaccharides (Banat et al., 2010), and glycoglycerolipids (Wicke et al., 2000). The properties/applications of BSs include detergency, emulsification, foaming, dispersion, wetting, penetrating, thickening, microbial growth enhancement (e.g., oil-degrading bacteria), antimicrobial agents, metal sequestering, and resource recovering (oil recovery). These interesting properties allow BSs to have the ability to replace some of the most versatile chemical surfactants that are now in practice. In addition, BSs are promising natural surfactants that offer several advantages over chemically synthesized surfactants, such as in situ production using renewable substrates, lower toxicity, biodegradability, and ecological compatibility (Marchant and Banat, 2012a,b). Interest in BS research has been on the increase during the past two decades due to their interesting properties, yet the reason behind the production of BSs by many microorganisms remains mostly unknown. Several proposed physiological roles of BSs have been put forward including (1) increasing the surface area and bioavailability of hydrophobic water-insoluble substrates (e.g., oil-degrading microbes) (Ron and Rosenberg, 1999), (2) bacterial pathogenesis and quorum sensing and biofilm formation (e.g., Pseudomonas aeruginosa) (Davey et al., 2003), (3) antimicrobial for self-defense (e.g., antimicrobial activity of rhamnolipids) (Stanghellini and Miller, 1997), and (4) cell proliferation in the producing bacteria (e.g., viscosinamide production by P. fluorescens) (Nielsen et al., 1999). To isolate BS-producing microbes, combination of various screening methodologies has been studied (Maneerat and Phetrong, 2007; Satpute et al., 2008; Thavasi et al., 2011c) and extensively reviewed (Nerurkar et al., 2009; Satpute et al., 2010). Microbial communities like Acinetobacter, Arthrobacter, Pseudomonas, Halomonas, Bacillus, Rhodococcus, Enterobacter, Azotobacter, Corynebacterium, Lactobacillus, and yeast have been reported to produce BSs (Schulz et al., 1991; Passeri et al., 1992; Banat, 1993; Abraham et al., 1998; Maneerat et al., 2006; Thavasi et al., 2007, 2009, 2011a; Das et al., 2008a,b; Perfumo et al., 2010a). This chapter collates and highlights data search on isolation, culture methods, and potential applications for BSs from marine microbes.