Rhamnolipids Characteristics, Production, Applications, and Analysis - Biosurfactants: Research Trends and Applications - page 52

TABLE 3.1
Properties of Rhamnolipids

Property Description

Surface tension (mN/m) 30

pH of aqueous solution 6.5-7.5

Critical micelle concentration (mg/L) 25

Appearance Dark reddish brown solution

Solubility Soluble at neutral pH

Volatility Not volatile

Specific gravity at 25°C 1.05-1.15

Molecular weight 504 (Rha1), 650 (Rha2)

Formula C 26 H 45 O 9 (monorhamnolipids), C 32 H 58 O 13 (dirhamnolipids)

Source: Adapted from Jeneil Biosurfactants Co., 2006.

emulsifying properties, it has shown a vast potential in different fields (Lotfabad
et al., 2010). There have been many investigations focused on this biosurfactant in
order to decode its biosynthetic pathway (Abdel-Mawgoud et al., 2011). In recent
years, with the advancement of accurate methods of analysis, there have been sig-
nificant advances in understanding these biomaterials.
The research on rhamnolipids and their production resulted in developing a range
of techniques for the isolation of few different rhamnolipid-producing bacterial
strains, characterization of rhamnolipid homologues and congeners, and unraveling
of the genetic details underlying rhamnolipid production in P. aeruginosa (Abdel-
Mawgoud et al., 2010; Rezanka et al., 2011). P. aeruginosa is a common bacterium
that is able to survive in a variety of environments. These bacteria are easy to be
cultivated, and after relatively short incubation periods, they are able to produce
relatively high yields of rhamnolipids (Nguyen and Sabatini, 2011).

RHAMNOLIPID-PRODUCING MICROORGANISMS
In recent years, there have been many studies to find new species of microorgan-
isms that are able to produce rhamnolipid. By reviewing the articles, it has been
noticed that most rhamnolipid-producing strains were found and isolated from the
oil-contaminated soils around refineries. In those harsh environments, with high
salinity and lack of other sources of carbon and nutrients, these microorganisms
evolved to survive and to use hydrocarbons as a source of carbon. As well, they
adapt to survive in both aerobic and anaerobic environments. One of the survival
strategies of these microorganisms consists of producing rhamnolipids. These
organic compounds help the bacteria to move easily toward the source of food or
away from a place where the level of nutrients is lower and has a high level of tox-
ins, as well as eliminating the competitors. Rhamnolipids solubilize hydrocarbons
in order to be absorbed through the cell membrane of the bacteria. Furthermore,
Kaczorek et al. (2012) reported that the rhamnolipid changes the cell surface of the