Enhancement of Remediation Technologies with Biosurfactants - Biosurfactants: Research Trends and Applications - page 239

TABLE 10.1 (continued)
Type and Microbial Origin of Biosurfactants Used
in Environmental Applications
Type of Surfactant Microorganism

Candida lipolytica

Bioemulsan BS 29 Gardonia sp.

Glycoprotein
Alasan Acinetobacter radioresistens

Particulate surfactant (PM) Pseudomonas marginalis

Biosur PM Pseudomonas maltophilla

Source: Adapted from Mulligan, C.N. and Gibbs, B.F., Factors influencing the economics of
biosurfactants, in Biosurfactants, Production, Properties, Applications , Kosaric, N. (ed.),
Marcel Dekker, New York, 1993, pp. 329-371.

ENVIRONMENTAL APPLICATIONS OF BIOSURFACTANTS

r hamnoliPiDs

Effect of Rhamnolipids on Contaminant Biodegradation
Petroleum Hydrocarbons
The various components of petroleum hydrocarbons are alkanes (also called aliphatic
compounds), cycloalkanes, aromatics, PAHs, asphaltenes, and resins. Alkanes, rep-
resented by the formula C 2 H 2n+2 , (where n is the number of carbons and 2n + 2 is the
number of hydrogens), increase in the number of isomers as the number of carbons
increases; low molecular weight alkanes are easily degraded by microorganisms.
Various studies have examined the effect of rhamnolipids on biodegradation of
organic contaminants with mixed results. There has been a particular focus on vari-
ous hydrocarbons of low solubility. A review by Maier and Soberon-Chavez (2000)
indicated that rhamnolipid addition can enhance biodegradation of hexadecane,
tetradecane, pristine, creosote, and hydrocarbon mixtures in soils, in addition to
hexadecane, octadecane, n-paraffin, and phenanthrene in liquid systems. Two mech-
anisms for enhanced biodegradation are possible: enhanced interaction with the cell
surface, which increases the hydrophobicity of the surface allowing hydrophobic
substrates to permeate more easily, and increased solubility of the substrate for the
microbial cells as shown in Figure 10.5 (Shreve et al., 1995, Zhang and Miller, 1992).
Zhang and Miller (1992) demonstrated that a concentration of 300 mg/L of rham-
nolipids increased the mineralization of octadecane to 20% compared to 5% for the
controls. Beal and Betts (2000) showed that the cell surface hydrophobicity during
growth on hexadecane increased by the biosurfactant strain more than a nonbiosur-
factant-producing one. The rhamnolipids also increased the hexadecane solubility to
22.8 from 1.8 μg/L. Other studies by Churchill et al. (1995) showed that rhamnolipid
addition with a fertilizer (Inipol EAp-22) enhanced biodegradation of aromatic and
aliphatic compounds in aqueous phase and soil reactors.