Amphiphilic Molecules of Microbial Origin Classification, Characteristics, Genetic Regulations, and Pathways for Biosynthesis - Biosurfactants: Research Trends and Applications - page 37

lipopolysaccharide and 20% (w/w) high-molecular weight exopolysaccharide
(Mercaldi et al., 2008). Production of extracellular bioemulsifiers is a widespread
phenomenon in Acinetobacter species. Acinetobacter radioresistens KA53 pro-
duced a bioemulsifier called alasan, composed of a heteropolysaccharide contain-
ing covalently bound alanine and proteins. Liposan is another effective emulsifier
produced by Candida lipolytica capable of forming stable oil-in-water emulsions
with a variety of commercial vegetable oils. It is composed of approximately 83%
carbohydrate and 17% protein, and the carbohydrate content is almost similar to
that of the emulsan (Cirigliano and Carman, 1985). Generally, the production of
emulsifying agents from yeast sources occurs in the presence of water-immiscible
substrates, but Sarubbo et al. reported the production of an emulsifier by C. lipolytica
using glucose as the carbon source (Sarubbo et al., 2001). They described that the bio-
synthesis of a bioemulsifier was not simply a prerequisite for the degradation of extra-
cellular hydrocarbon. Amaral et al. isolated and characterized an emulsifier from the
glucose-based culture medium of Yarrowia lipolytica IMUFRJ50682, which exhib-
ited emulsification activities superior to liposan and named it as yansan. It was able
to form stable emulsions of both aromatic and aliphatic hydrocarbons (Amaral et al.,
2006). Streptomyces sp. S1 produced a bioemulsifier composed of 82% protein, 17%
polysaccharide and 1% reducing sugar. The bioemulsifier had significant emulsifying
properties and also reduced ST of the medium (Kokare et al., 2007). Gutiérrez et al.
reported the production of high-molecular weight glycoprotein emulsifiers from two
marine Halomonas species. They showed the highest reported emulsifying activities
derived from a Halomonas species (Gutiérrez et al., 2007). Polymeric biosurfactants
from P. aeruginosa (Koronelli et al., 1983) and P. nautica (Husain et al., 1997) have
also been shown to have significant emulsification properties.
P artiCulate B iosurfaCtants
Extracellular vesicles that help in hydrocarbon uptake by cells and microbial cells
with surface active properties are referred to as particulate biosurfactants. Serratia
marcescens NS 38 produced extracellular vesicles, and their main lipid component
had strong wetting activity. In addition to the wetting agent, a red pigment (pro-
digiosin) was also present in the vesicle (Matsuyama et al., 1986). Acinetobacter sp.
HO1-N produced extracellular membrane vesicles with 20-50 nm diameter and a
buoyant density of 1.158 g/cm 3 . They were rich in phospholipid and lipopolysaccha-
ride, exhibiting good emulsification activity (Kappeli and Finnerty, 1979). Surfactant
activity in most hydrocarbon-degrading and pathogenic bacteria is attributed to sev-
eral cell surface components.
SALIENT CHARACTERISTICS OF MICROBIAL AMPHIPHILES
s urfaCe anD i interfaCe a Ctivity
Surfactin and lichenysin are the most powerful biosurfactants in reducing ST at
low CMC values. Lichenysin A, a lipopeptide from B. licheniformis , can reduce
the ST of water to 28 mN/m at a CMC as low as 12 mg/L (Yakimov et al., 1995).