hydrocarbon-degrading bacteria, with a high presence of mobile genetic elements
and proteins for signal transduction, but it shows a very narrow substrate profile
(Toshchakov et al. 2017). The psychrophilic strains belonging to Oleispira sp. are
able to use hydrocarbons as carbon source (Table 7.1) in a range of temperature
comprised between 4
C and 20
C (Yakimov et al. 2003; Kube et al. 2013; Crisafi
et al. 2016). Oleispira have been detected and isolated both in polar region and deepsea waters demonstrating that Oleispira spp. has peculiar capability in the adaptation
to extreme parameters such as high hydrostatic pressure and low temperature
(Marietou et al. 2018; Jensen et al. 2019). Strictly related to Thalassolituus genus,
Oleibacter sp. was isolated from tropical region and showed capability to degrade
petroleum aliphatic hydrocarbons growing between the range 10–40
C but the
optimum is 25–30
C (Teramoto et al. 2011). It was also described in high-polluted
marine sediments (Catania et al. 2015). Marine aliphatic-degrading strains show
similar metabolic pathways. On the base of Alcanivorax model, the best-known
obligate hydrocarbon-degrading bacteria specialists, together with the knowledge
about the generalist Pseudomonas sp., a general degradation pathway for the aerobic
alkane degradation has been proposed. The alkane-activating enzymes, monooxygenases, generate a primary alcohol by the oxidation of a terminal methyl
group. The primary alcohol is oxidized to aldehyde, and then converted into a
fatty acid that is conjugated to coenzyme A, which is further processed by
β-oxidation to generate acetyl-coenzyme A (Morgan and Watkinson 1990; van
Hamme et al. 2003; Ashraf 1994; Schneiker et al. 2006; Wentzel et al. 2007;
Gregson et al. 2018). Subterminal oxidation of n-alkanes generates a secondary
alcohol that is then converted to the corresponding ketone, and transformed in ester
by the oxidation catalyzed by Baeyer–Villiger mono-oxygenase. (Whyte et al. 1998;
Kotani et al. 2006). The action of an esterase generates an alcohol and a fatty acid
(Forney and Markovetz 1970; Sakuradani et al. 2013). Both terminal and subterminal oxidation can coexist in some microorganisms as in Thalassolituus sp. that
express this pathway with long-chain alkanes growth (Gregson et al. 2018).
Alcanivorax sp. and Oleispira sp. strains show similar patterns of expression profile.
Their central operon is a cluster of genes: alkSB 1 GHJ for hydrocarbons catabolism
(Kube et al. 2013; Schneiker et al. 2006), in particular AlkB 1 and AlkB 2 alkane
hydroxylase (monoxygenase) oxidize medium-chain alkanes (C5–C12) mediumchain alkanes in the range (C8–C16), respectively. (Schneiker et al. 2006; van
Beilen et al. 2006). An additional gene AlmA, a flavin-binding monooxygenase,
was recently identified in Alcanivorax dieselolei and seems to be upregulated in
presence of long-chain alkanes (Wang and Shao 2014). Moreover, genes involved
in the expression of ferredoxin, an alcohol dehydrogenase, FAD-dependent oxidoreductase are involved in the terminal oxidation of alkanes. In Alcanivorax SK2 the
presence of isoprenoid hydrocarbons determined the specifically expression of
three cytochromes P450, while in Oleispira they are differentially expressed in
tetradecane and acetate (Schneiker et al. 2006; Kube et al. 2013; Sevilla et al.
2017). Also Marinobacter sp. shows similar patterns with a key role of homologous
genes. By contrast, the orthologous to AlmA, a flavin-binding monooxygenase gene
involved in long-chain hydrocarbon (>32 carbons) degradation in Acinetobacter and
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R. Denaro et al.
and proteins for signal transduction, but it shows a very narrow substrate profile
(Toshchakov et al. 2017). The psychrophilic strains belonging to Oleispira sp. are
able to use hydrocarbons as carbon source (Table 7.1) in a range of temperature
comprised between 4
C and 20
C (Yakimov et al. 2003; Kube et al. 2013; Crisafi
et al. 2016). Oleispira have been detected and isolated both in polar region and deepsea waters demonstrating that Oleispira spp. has peculiar capability in the adaptation
to extreme parameters such as high hydrostatic pressure and low temperature
(Marietou et al. 2018; Jensen et al. 2019). Strictly related to Thalassolituus genus,
Oleibacter sp. was isolated from tropical region and showed capability to degrade
petroleum aliphatic hydrocarbons growing between the range 10–40
C but the
optimum is 25–30
C (Teramoto et al. 2011). It was also described in high-polluted
marine sediments (Catania et al. 2015). Marine aliphatic-degrading strains show
similar metabolic pathways. On the base of Alcanivorax model, the best-known
obligate hydrocarbon-degrading bacteria specialists, together with the knowledge
about the generalist Pseudomonas sp., a general degradation pathway for the aerobic
alkane degradation has been proposed. The alkane-activating enzymes, monooxygenases, generate a primary alcohol by the oxidation of a terminal methyl
group. The primary alcohol is oxidized to aldehyde, and then converted into a
fatty acid that is conjugated to coenzyme A, which is further processed by
β-oxidation to generate acetyl-coenzyme A (Morgan and Watkinson 1990; van
Hamme et al. 2003; Ashraf 1994; Schneiker et al. 2006; Wentzel et al. 2007;
Gregson et al. 2018). Subterminal oxidation of n-alkanes generates a secondary
alcohol that is then converted to the corresponding ketone, and transformed in ester
by the oxidation catalyzed by Baeyer–Villiger mono-oxygenase. (Whyte et al. 1998;
Kotani et al. 2006). The action of an esterase generates an alcohol and a fatty acid
(Forney and Markovetz 1970; Sakuradani et al. 2013). Both terminal and subterminal oxidation can coexist in some microorganisms as in Thalassolituus sp. that
express this pathway with long-chain alkanes growth (Gregson et al. 2018).
Alcanivorax sp. and Oleispira sp. strains show similar patterns of expression profile.
Their central operon is a cluster of genes: alkSB 1 GHJ for hydrocarbons catabolism
(Kube et al. 2013; Schneiker et al. 2006), in particular AlkB 1 and AlkB 2 alkane
hydroxylase (monoxygenase) oxidize medium-chain alkanes (C5–C12) mediumchain alkanes in the range (C8–C16), respectively. (Schneiker et al. 2006; van
Beilen et al. 2006). An additional gene AlmA, a flavin-binding monooxygenase,
was recently identified in Alcanivorax dieselolei and seems to be upregulated in
presence of long-chain alkanes (Wang and Shao 2014). Moreover, genes involved
in the expression of ferredoxin, an alcohol dehydrogenase, FAD-dependent oxidoreductase are involved in the terminal oxidation of alkanes. In Alcanivorax SK2 the
presence of isoprenoid hydrocarbons determined the specifically expression of
three cytochromes P450, while in Oleispira they are differentially expressed in
tetradecane and acetate (Schneiker et al. 2006; Kube et al. 2013; Sevilla et al.
2017). Also Marinobacter sp. shows similar patterns with a key role of homologous
genes. By contrast, the orthologous to AlmA, a flavin-binding monooxygenase gene
involved in long-chain hydrocarbon (>32 carbons) degradation in Acinetobacter and
202
R. Denaro et al.