synthetic surfactants may be the use of in situ biosurfactant-producing (and
pollutant-biodegrading) microorganisms in bioremediation technologies (Ángeles
and Refugio 2013; Hosseininoosheri et al. 2016). Another promising approach to
making biosurfactants cost-competitive is the optimization of cultivation conditions
(Soares dos Santos et al. 2016) or the use of improved GMO producers (Sekhon et al.
2011; Martins Das Neves et al. 2007).
24.2.3 Specific Properties of Biosurfactants
Generally, biosurfactants show very low or no toxicity, thus they can be widely used
in remediation protocols. On the other hand, biosurfactants induce an increase in
bioavailability and mobility of toxic compounds that can cause secondary toxic
effects against some biota. For example, tests evaluating the seed germination and
growth inhibition showed an increase in the phytotoxicity of diesel oil for four
terrestrial plant species (alfalfa, sorghum, mustard, and cuckooflower) after the
addition of rhamnolipids (Marecik et al. 2012).
Rhamnolipids, as surfactants, can negatively affect microbial cell adhesion and/or
biofilm development, thus they can be used to control the microbial biofilm. On the
other hand, biosurfactants may exhibit toxicity against some pathogenic microorganisms; therefore, they can counteract human (Das et al. 2008) or plant (Borah et al.
2016) pathogens.
The action of biosurfactants or bioemulsifiers on the environment intensifies the
cell–pollutant interactions, thus increasing the pollutant bioavailability. Microorganisms gain direct access to water-solubilized hydrocarbons, heavy metals, or pesticides; their cells have direct contact with released oil as a separate phase in the form
of large drops, pseudosolubilized, or emulsified oil (Zhong et al. 2014; Alvarez Yela
et al. 2016; Yang et al. 2016). Microorganisms usually uptake exterior watersolubilized and pseudosolubilized hydrocarbon molecules; however, an alternate
mechanism similar to active pinocytosis in appearance, by which small rhamnolipidcoated hexadecane droplets were transported through the membrane to cell interior,
was proved to exist for Pseudomonas sp. (Cameotra and Singh 2009).
Incensement of pollutants’ mobility and bioavailability can fundamentally
increase the efficiency of remediation techniques like washing or microorganismbased remediation, e.g., bioremediation or bioaugmentation. Depending on the
concentration and molecular weight, three basic modes of biosurfactant action can
be distinguished, i.e., mobilization, solubilization, and emulsification (PacwaPłociniczak et al. 2011). Mobilization occurs under a biosurfactant concentration
below CMC when the adsorbed organic compounds are desorbed from a matrix by
means of biosurfactants breaking free as separate molecules to become (bio)available in the aqueous phase.
Schematic mechanisms of the action of both low- and high-molecular-mass
biosurfactants in soil are shown in Figs. 24.1 and 24.2, respectively. By contrast,
solubilization occurs under biosurfactant concentrations above CMC and leads to
24 Modern Bioremediation Approaches: Use of Biosurfactants, Emulsifiers. . .
499
pollutant-biodegrading) microorganisms in bioremediation technologies (Ángeles
and Refugio 2013; Hosseininoosheri et al. 2016). Another promising approach to
making biosurfactants cost-competitive is the optimization of cultivation conditions
(Soares dos Santos et al. 2016) or the use of improved GMO producers (Sekhon et al.
2011; Martins Das Neves et al. 2007).
24.2.3 Specific Properties of Biosurfactants
Generally, biosurfactants show very low or no toxicity, thus they can be widely used
in remediation protocols. On the other hand, biosurfactants induce an increase in
bioavailability and mobility of toxic compounds that can cause secondary toxic
effects against some biota. For example, tests evaluating the seed germination and
growth inhibition showed an increase in the phytotoxicity of diesel oil for four
terrestrial plant species (alfalfa, sorghum, mustard, and cuckooflower) after the
addition of rhamnolipids (Marecik et al. 2012).
Rhamnolipids, as surfactants, can negatively affect microbial cell adhesion and/or
biofilm development, thus they can be used to control the microbial biofilm. On the
other hand, biosurfactants may exhibit toxicity against some pathogenic microorganisms; therefore, they can counteract human (Das et al. 2008) or plant (Borah et al.
2016) pathogens.
The action of biosurfactants or bioemulsifiers on the environment intensifies the
cell–pollutant interactions, thus increasing the pollutant bioavailability. Microorganisms gain direct access to water-solubilized hydrocarbons, heavy metals, or pesticides; their cells have direct contact with released oil as a separate phase in the form
of large drops, pseudosolubilized, or emulsified oil (Zhong et al. 2014; Alvarez Yela
et al. 2016; Yang et al. 2016). Microorganisms usually uptake exterior watersolubilized and pseudosolubilized hydrocarbon molecules; however, an alternate
mechanism similar to active pinocytosis in appearance, by which small rhamnolipidcoated hexadecane droplets were transported through the membrane to cell interior,
was proved to exist for Pseudomonas sp. (Cameotra and Singh 2009).
Incensement of pollutants’ mobility and bioavailability can fundamentally
increase the efficiency of remediation techniques like washing or microorganismbased remediation, e.g., bioremediation or bioaugmentation. Depending on the
concentration and molecular weight, three basic modes of biosurfactant action can
be distinguished, i.e., mobilization, solubilization, and emulsification (PacwaPłociniczak et al. 2011). Mobilization occurs under a biosurfactant concentration
below CMC when the adsorbed organic compounds are desorbed from a matrix by
means of biosurfactants breaking free as separate molecules to become (bio)available in the aqueous phase.
Schematic mechanisms of the action of both low- and high-molecular-mass
biosurfactants in soil are shown in Figs. 24.1 and 24.2, respectively. By contrast,
solubilization occurs under biosurfactant concentrations above CMC and leads to
24 Modern Bioremediation Approaches: Use of Biosurfactants, Emulsifiers. . .
499