cationic biosurfactants can replace the same charged metal ions by competition
and any types of biosurfactants can simply release metals bonded to micelles
(Pacwa-Płociniczak et al. 2011).
While in the bulk aqueous phase, the above-mentioned processes are carried out
as described; the sorption on particles may reduce the biosurfactant effective concentration in more complex systems with water–solid interfaces (represented by wet
soil or sediment). Singh and Cameotra (2013) stated a 50% adsorption of a
lipopeptide biosurfactant on soil. This phenomenon combined with the biosurfactant
biodegradation should be taken into account when determining the required amount
of a biosurfactant for the given task (Maslin and Maier 2000; Ochoa-Loza et al.
2007). To address this problem, a pulse strategy (with a periodic addition of
biosurfactant into the system) is often used (Maslin and Maier 2000). However,
whenever possible, the best strategy is an in situ (natural or enhanced) production of
biosurfactants by suitable species (Hosseininoosheri et al. 2016). The other common
setback is that biosurfactants accumulated at the water–gas interface significantly
decrease the oxygen mass transfer from the gas to aqueous phase (Sheppard and
Cooper 1990), thus potentially causing an oxygen depletion, which can negatively
affect remediation bioprocesses.
The above-mentioned influence of biosurfactants on pollutant availability could
be accompanied by their influence on microorganisms. The protective function of
biosurfactants against toxic compounds described in several publications can be
utilized in remediation techniques (Maslin and Maier 2000; Chrzanowski et al.
2009). In addition, biosurfactants can increase the cell wall hydrophobicity, thus
enhancing the degradation of hydrophobic compounds by Pseudomonas aeruginosa
strains with a low cell wall hydrophobicity. However, the action of other strains with
low cell wall hydrophobicity was not enhanced (Zhang and Miller 1994). The
mechanism of this process was studied in detail by Al-Tahhan et al. (2000). They
found that rhamnolipids increase the cell surface hydrophobicity by releasing the
genus-specific lipopolysaccharides from the outer membrane of Pseudomonas
aeruginosa. Another mechanism for Pseudomonas aeruginosa was described by
Sotirova et al. (2009) when the cell surface hydrophobicity was increased by
changing the composition of outer membrane proteins in the presence of a
rhamnolipid.
24.2.4 Application Potential of Biosurfactants
24.2.4.1 Treatment of the Sites Contaminated by Organic Pollutants
Hydrocarbon contamination is one of the major environmental problems that result
from the activities related to the petrochemical industry. Small-scale field experiments
conducted by Tahseen et al. (2016) showed a significant improvement in
oil-contaminated soil remediation as a result of rhamnolipid addition. The addition
of rhamnolipids caused a greater effect than the addition of mineral nutrients in the
502
M. Halecký and E. Kozliak
and any types of biosurfactants can simply release metals bonded to micelles
(Pacwa-Płociniczak et al. 2011).
While in the bulk aqueous phase, the above-mentioned processes are carried out
as described; the sorption on particles may reduce the biosurfactant effective concentration in more complex systems with water–solid interfaces (represented by wet
soil or sediment). Singh and Cameotra (2013) stated a 50% adsorption of a
lipopeptide biosurfactant on soil. This phenomenon combined with the biosurfactant
biodegradation should be taken into account when determining the required amount
of a biosurfactant for the given task (Maslin and Maier 2000; Ochoa-Loza et al.
2007). To address this problem, a pulse strategy (with a periodic addition of
biosurfactant into the system) is often used (Maslin and Maier 2000). However,
whenever possible, the best strategy is an in situ (natural or enhanced) production of
biosurfactants by suitable species (Hosseininoosheri et al. 2016). The other common
setback is that biosurfactants accumulated at the water–gas interface significantly
decrease the oxygen mass transfer from the gas to aqueous phase (Sheppard and
Cooper 1990), thus potentially causing an oxygen depletion, which can negatively
affect remediation bioprocesses.
The above-mentioned influence of biosurfactants on pollutant availability could
be accompanied by their influence on microorganisms. The protective function of
biosurfactants against toxic compounds described in several publications can be
utilized in remediation techniques (Maslin and Maier 2000; Chrzanowski et al.
2009). In addition, biosurfactants can increase the cell wall hydrophobicity, thus
enhancing the degradation of hydrophobic compounds by Pseudomonas aeruginosa
strains with a low cell wall hydrophobicity. However, the action of other strains with
low cell wall hydrophobicity was not enhanced (Zhang and Miller 1994). The
mechanism of this process was studied in detail by Al-Tahhan et al. (2000). They
found that rhamnolipids increase the cell surface hydrophobicity by releasing the
genus-specific lipopolysaccharides from the outer membrane of Pseudomonas
aeruginosa. Another mechanism for Pseudomonas aeruginosa was described by
Sotirova et al. (2009) when the cell surface hydrophobicity was increased by
changing the composition of outer membrane proteins in the presence of a
rhamnolipid.
24.2.4 Application Potential of Biosurfactants
24.2.4.1 Treatment of the Sites Contaminated by Organic Pollutants
Hydrocarbon contamination is one of the major environmental problems that result
from the activities related to the petrochemical industry. Small-scale field experiments
conducted by Tahseen et al. (2016) showed a significant improvement in
oil-contaminated soil remediation as a result of rhamnolipid addition. The addition
of rhamnolipids caused a greater effect than the addition of mineral nutrients in the
502
M. Halecký and E. Kozliak