Biosurfactants and Bioemulsifiers from Marine Sources - Biosurfactants: Research Trends and Applications - page 126

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 pro-
duction 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) antimi-
crobial 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 pro-
duce 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.
MARINE BIOSURFACTANTS
Biosurfactants from marine microbes : A detailed list of BSs from marine microbes is
described (Table 5.1) and a graphic representation of the number of publications and
their percentages are illustrated in Figures 5.1 through 5.4. Earlier reports on BSs of
marine origin mainly focused on environmental remediation applications of BSs
such as emulsifiers and dispersants or BSs from oil-degrading microbes (Rosenberg
et al., 1979; Schulz et al., 1991; Yakimov et al., 1998; Thavasi and Jayalakshmi,
2003, Thavasi et al., 2006, 2009, 2008, 2011a; Peng et al., 2007, 2008) and other
potential applications such as medical and industrial sectors have not been studied
extensively (Rodrigues et al., 2006b; Marchant and Banat, 2012a,b). Recently the
trend has changed, and scientists started focusing on other potential application/
properties of marine BSs such as antimicrobial (Mukherjee et al., 2009), biofilm
disruption (Kiran et al., 2010a), and nanoparticle synthesis (Kiran et al., 2010b).
A detailed description of marine microbial surfactants, their composition, and pro-
ducing organism are described in the following sections.
Glycolipids and glycoglycerolipids : Glycolipids are the most studied surfactants
among all other marine microbial BSs, that is, 48% of the publications on marine
BSs are about glycolipid BSs (Figure 5.1). Glycolipid BSs include glycolipids, glucose
lipid, trehalose lipids, trehalose tetraester, trehalose corynomycolates, rhamnolipids,
mannosylerythritol lipids, sophorolipids, and extracellular polysaccharide-lipids
(ESLs). Glycolipids are composed of a hydrophobic fatty acid moiety esterified to
a hydrophilic carbohydrate moiety. The sugar components of the glycolipids may
be one or two molecules of glucose, trehalose, mannose, sophorose, or rhamnose.