accessibility to the contaminants often constitutes a major factor limiting the biodegradation rate, some microorganisms have developed a strategy to overcome
it. Mycobacterium species has developed unique ability to reach the surface of
highly hydrophobic contaminants by adhesion caused probably by the presence of
high amounts of mycolic acids in the cell walls (Pagnout et al. 2006). Other bacteria
species like Pseudomonas aeruginosa produce biosurfactants like rhamnolipids to
increase bioavailability of hydrophobic compounds (Rahman et al. 2002).
The ability to metabolize wide spectrum of organic compounds including potentially toxic substances is favorable in the evolutionary process. The wider the
metabolic capacities of the strain, the better the fitness of the microbial colony
during depletion of preferable carbon source. Microorganisms developed many
systems enabling survival in diverse and unstable environments. For example,
wide substrate range of enzymes allows binding of many compounds with similar
structure in an active center. This ability can be crucial taking into account the
diverse composition of petroleum contaminants. Another strategy to metabolize
different hydrocarbons is the use of many enzymes with different substrate range,
in which expression is induced by the current type of available carbon sources
(Fuentes et al. 2014). Additionally, the ability to metabolize toxic compounds provides an opportunity to function while other sources of carbon and energy will be
depleted (Fuentes et al. 2014).
5.2.2 Biodegradation of Aliphatic Hydrocarbons
Metabolic pathway of hydrocarbon degradation is a specific process among different
bacterial and fungi species; nevertheless some similarities can be observed over
aerobic catabolism. In case of alkanes (Fig. 5.2), hydroxylation reaction is catalyzed
by alkane oxygenases, which is a diverse group of enzymes incorporating bacterial
particulate alkane hydroxylases (pAHs) or a cytochrome P450 alkane hydroxylases
(van Beilen and Funhoff 2007). The studies on pAH of a Pseudomonas putida
isolate GPo1 revealed that the enzyme is integral membrane non-hemediiron
monooxygenases of the AlkB-type (van Beilen and Funhoff 2007). These enzymes
cooperate with mononuclear iron rubredoxin reductase and dinuclear iron
rubredoxin to transfer electrons form NADH to the active site (Wentzel et al.
2007). AlkB-type enzymes were found within genera like Acinetobacter,
Alcanivorax, Burkholderia, Mycobacterium, Pseudomonas, Rhodococcus and were
identified with the biodegradation of C5–C16 alkanes, fatty acids, alkylbenzenes,
and cycloalkanes. Although, some of alkB monooxygenases oxidize short-chain
alkanes, most of them prefer long-chained hydrocarbons with carbon chain longer
than C10 (van Beilen and Funhoff 2007). P450 alkane hydroxylases are more
frequently reported for yeasts than bacteria. In the study of Maier et al. (2001) the
sequence of cytochrome P450 was found in isolates grown on C5–C10 alkanes.
Further analysis has confirmed that the enzyme was responsible for hydrocarbon
degradation (van Beilen et al. 2006).
5 Potential Use of Waste-to-Bioenergy By-Products in Bioremediation of Total. . .
253
it. Mycobacterium species has developed unique ability to reach the surface of
highly hydrophobic contaminants by adhesion caused probably by the presence of
high amounts of mycolic acids in the cell walls (Pagnout et al. 2006). Other bacteria
species like Pseudomonas aeruginosa produce biosurfactants like rhamnolipids to
increase bioavailability of hydrophobic compounds (Rahman et al. 2002).
The ability to metabolize wide spectrum of organic compounds including potentially toxic substances is favorable in the evolutionary process. The wider the
metabolic capacities of the strain, the better the fitness of the microbial colony
during depletion of preferable carbon source. Microorganisms developed many
systems enabling survival in diverse and unstable environments. For example,
wide substrate range of enzymes allows binding of many compounds with similar
structure in an active center. This ability can be crucial taking into account the
diverse composition of petroleum contaminants. Another strategy to metabolize
different hydrocarbons is the use of many enzymes with different substrate range,
in which expression is induced by the current type of available carbon sources
(Fuentes et al. 2014). Additionally, the ability to metabolize toxic compounds provides an opportunity to function while other sources of carbon and energy will be
depleted (Fuentes et al. 2014).
5.2.2 Biodegradation of Aliphatic Hydrocarbons
Metabolic pathway of hydrocarbon degradation is a specific process among different
bacterial and fungi species; nevertheless some similarities can be observed over
aerobic catabolism. In case of alkanes (Fig. 5.2), hydroxylation reaction is catalyzed
by alkane oxygenases, which is a diverse group of enzymes incorporating bacterial
particulate alkane hydroxylases (pAHs) or a cytochrome P450 alkane hydroxylases
(van Beilen and Funhoff 2007). The studies on pAH of a Pseudomonas putida
isolate GPo1 revealed that the enzyme is integral membrane non-hemediiron
monooxygenases of the AlkB-type (van Beilen and Funhoff 2007). These enzymes
cooperate with mononuclear iron rubredoxin reductase and dinuclear iron
rubredoxin to transfer electrons form NADH to the active site (Wentzel et al.
2007). AlkB-type enzymes were found within genera like Acinetobacter,
Alcanivorax, Burkholderia, Mycobacterium, Pseudomonas, Rhodococcus and were
identified with the biodegradation of C5–C16 alkanes, fatty acids, alkylbenzenes,
and cycloalkanes. Although, some of alkB monooxygenases oxidize short-chain
alkanes, most of them prefer long-chained hydrocarbons with carbon chain longer
than C10 (van Beilen and Funhoff 2007). P450 alkane hydroxylases are more
frequently reported for yeasts than bacteria. In the study of Maier et al. (2001) the
sequence of cytochrome P450 was found in isolates grown on C5–C10 alkanes.
Further analysis has confirmed that the enzyme was responsible for hydrocarbon
degradation (van Beilen et al. 2006).
5 Potential Use of Waste-to-Bioenergy By-Products in Bioremediation of Total. . .
253