environment, thus maintaining a suitable enzyme activity at non-ideal pH, ionic
strength, and temperature as well as in the presence of light (photodegradation),
proteolytic enzymes, and toxic heavy metals (Tietjen and Wetzel 2003;
Quiquampoix et al. 2002; Wang et al. 2017; Wang et al. 2014).
On the other hand, many adverse effects resulting from enzyme–soil interactions
decreasing enzyme activity have been described as well, namely: conformational
changes, interfacial pH affection, diffusion-limiting kinetics, orientation effects
(steric factors), restriction of co-enzyme availability, enzyme encapsulation or denaturation by organic matter or toxic metals, and enzymes’ degradation by oxidative
minerals (Quiquampoix et al. 2002; Zimmerman and Ahn 2010).
24.3.2 Evaluation of Using Enzymes for Bioremediation
Advantages and disadvantages of enzymes over microorganisms for their use in
bioremediation are summarized in Table 24.2. While free enzymes tend to lower
mass transfer limitations resulting in faster reactions, immobilized enzymes, either
the artificially attached to suitable particles or the naturally immobilized on soil
particles, show significant mass transfer limitations (Datta et al. 2017; Quiquampoix
et al. 2002). Enzymes can be applied under the lack of substances or conditions
essential for live cell functioning, thus eliminating the limitations of nutrient availability, cell acclimation, formation of metabolic by-products, inhibition by other
present cell-toxic chemicals. This creates the possibility of their application to toxic
or concentrated cell-inhibiting compounds as well as to harsh operational conditions,
e.g., extreme pH, temperature, and ionic strength/salinity (Huang et al. 2009;
Gianfreda et al. 2016). While the introduction of non-native microbial species is
common and mostly non-controversial, yet a subject to approval by state authorities,
the introduction of genetically modified microorganisms is strictly regulated and
rarely publically acceptable. However, both non-native and genetically modified
species can be replaced by enzymes, either native or engineered, presumably with no
ecological impact.
The key disadvantage is still the high cost of enzyme application, despite the
advances in enzyme production, isolation and purification, potential of the use of
genetically engineered enzymes and their hyperproduction by genetically modified
species (Eibes et al. 2015). Total mineralization of the majority of complex polluting
molecules is undermined by the existence of complex degradation pathways involving many different enzymes. Single enzymes usually only “detoxify” a given
pollutant by a single-step chemical modification and thus reduce its toxicity by
cleaving a specific group (Acevedo et al. 2010; Daâssi et al. 2016). This limitation
can be addressed by applying either mixtures of free enzymes or enzymatic
nanoparticles (constructed or natural) that have all the necessary enzymes attached
to them. However, the cost of such an advanced bioremediation application is
enormous. In addition, it must be ensured that the action of each essential enzyme
occurs with the same substrate molecule but at a different time.
24 Modern Bioremediation Approaches: Use of Biosurfactants, Emulsifiers. . .
507
strength, and temperature as well as in the presence of light (photodegradation),
proteolytic enzymes, and toxic heavy metals (Tietjen and Wetzel 2003;
Quiquampoix et al. 2002; Wang et al. 2017; Wang et al. 2014).
On the other hand, many adverse effects resulting from enzyme–soil interactions
decreasing enzyme activity have been described as well, namely: conformational
changes, interfacial pH affection, diffusion-limiting kinetics, orientation effects
(steric factors), restriction of co-enzyme availability, enzyme encapsulation or denaturation by organic matter or toxic metals, and enzymes’ degradation by oxidative
minerals (Quiquampoix et al. 2002; Zimmerman and Ahn 2010).
24.3.2 Evaluation of Using Enzymes for Bioremediation
Advantages and disadvantages of enzymes over microorganisms for their use in
bioremediation are summarized in Table 24.2. While free enzymes tend to lower
mass transfer limitations resulting in faster reactions, immobilized enzymes, either
the artificially attached to suitable particles or the naturally immobilized on soil
particles, show significant mass transfer limitations (Datta et al. 2017; Quiquampoix
et al. 2002). Enzymes can be applied under the lack of substances or conditions
essential for live cell functioning, thus eliminating the limitations of nutrient availability, cell acclimation, formation of metabolic by-products, inhibition by other
present cell-toxic chemicals. This creates the possibility of their application to toxic
or concentrated cell-inhibiting compounds as well as to harsh operational conditions,
e.g., extreme pH, temperature, and ionic strength/salinity (Huang et al. 2009;
Gianfreda et al. 2016). While the introduction of non-native microbial species is
common and mostly non-controversial, yet a subject to approval by state authorities,
the introduction of genetically modified microorganisms is strictly regulated and
rarely publically acceptable. However, both non-native and genetically modified
species can be replaced by enzymes, either native or engineered, presumably with no
ecological impact.
The key disadvantage is still the high cost of enzyme application, despite the
advances in enzyme production, isolation and purification, potential of the use of
genetically engineered enzymes and their hyperproduction by genetically modified
species (Eibes et al. 2015). Total mineralization of the majority of complex polluting
molecules is undermined by the existence of complex degradation pathways involving many different enzymes. Single enzymes usually only “detoxify” a given
pollutant by a single-step chemical modification and thus reduce its toxicity by
cleaving a specific group (Acevedo et al. 2010; Daâssi et al. 2016). This limitation
can be addressed by applying either mixtures of free enzymes or enzymatic
nanoparticles (constructed or natural) that have all the necessary enzymes attached
to them. However, the cost of such an advanced bioremediation application is
enormous. In addition, it must be ensured that the action of each essential enzyme
occurs with the same substrate molecule but at a different time.
24 Modern Bioremediation Approaches: Use of Biosurfactants, Emulsifiers. . .
507