Alcanivorax species, showed no change in expression profile growing under the
same conditions (Wang and Shao 2012; Mounier et al. 2014). Biosurfactants, a
distinctive feature of hydrocarbon-degrading bacteria, enhance bioavailability of
hydrocarbons and improve the biodegradation capability of these hydrophobic
organic substrates (Kubicki et al. 2019). The Alcanivorax borkumensis SK2 produces anionic glycolipids biosurfactants with four varying chain lengths fatty acids
and surface-active secondary metabolites (Qiao and Shao 2010), Marinobacter
sp. exhibits a wide range of biosurfactants, which includes rhamnolipids (Tripathi
et al. 2019), but also amphiphilic siderophore (Martinez et al. 2000). To date, no
relevant evidences for biosurfactants production in Thalassolituus sp. and Oleispira
sp. have been reported, although they showed a differential expression, in oily and
non-oily seawater, of a LolA-like gene codifying for a lipoprotein, involved in
biosurfactant production (Schneiker et al. 2006; Sabirova et al. 2011; Gregson
et al. 2018). Alcanivorax genome includes putative genes for exopolysaccharides
biosynthesis, export, modification, and polymerization (Sabirova et al. 2011). Moreover, cluster for alginate biosynthesis and a number of determinants for a Type II
secretion system together with genes encoding for secretion proteins have been
identified in Marinobacter (Handley and Lloyd 2013; Mounier et al. 2018) and
Thalassolituus sp. (Morohoshi et al. 2018).
Bacteria-Degrading Aromatic Hydrocarbons
Different pattern of genes and enzymes have been described for polycyclic aromatic
hydrocarbons degradation. The widespread diffusion of polycyclic aromatic hydrocarbons in marine environment determines the presence of these compounds in
remote deep-sea sediments and hydrothermal vent sulfide minerals (Vila et al.
2015). In spite of their high toxicity, the marine bacteria can use the polycyclic
aromatic hydrocarbons as both carbon and energy sources. Table 7.1 shows some of
the strains described as polycyclic aromatic hydrocarbons-degraders. The classical
strategy for aromatic-ring cleavage, which is restricted to aerobic microorganisms,
comprises firstly the oxidation of the benzene ring to form cis-dihydrodiols catalyzed
by dioxygenase enzymes that are then dehydrogenated to form dihydroxylated
intermediates, further metabolized via catechols to water and carbon dioxide. Marine
bacteria show a wide biodiversity in metabolic pathways identified for polycyclic
aromatic hydrocarbons degradation. As an example, halophilic bacteria as
Halomonas use several downstream pathways, such as protocatechuic acid pathway,
gentisic acid pathway, and catechol pathway. Moreover, several downstream pathways to rapidly transform intermediates have been identified (Wang et al. 2018).
Cycloclasticus genus, one of the key players of polycyclic aromatic hydrocarbons
degradation in marine environment, can also degrade chlorinated derivatives of
polycyclic aromatic hydrocarbons (Dyksterhouse et al. 1995; Yakimov et al. 2007;
Yakimov et al. 2014). It has been detected in estuaries (Niepceron et al. 2010),
coastal areas (Genovese et al. 2014; Ding et al. 2017), deep-sea sediments (Wang
et al. 2008), and polar oceans (Hazen et al. 2010; Brakstad et al. 2015). Recently,
7 Biodegradation of Hydrocarbons in Marine Environment
203
same conditions (Wang and Shao 2012; Mounier et al. 2014). Biosurfactants, a
distinctive feature of hydrocarbon-degrading bacteria, enhance bioavailability of
hydrocarbons and improve the biodegradation capability of these hydrophobic
organic substrates (Kubicki et al. 2019). The Alcanivorax borkumensis SK2 produces anionic glycolipids biosurfactants with four varying chain lengths fatty acids
and surface-active secondary metabolites (Qiao and Shao 2010), Marinobacter
sp. exhibits a wide range of biosurfactants, which includes rhamnolipids (Tripathi
et al. 2019), but also amphiphilic siderophore (Martinez et al. 2000). To date, no
relevant evidences for biosurfactants production in Thalassolituus sp. and Oleispira
sp. have been reported, although they showed a differential expression, in oily and
non-oily seawater, of a LolA-like gene codifying for a lipoprotein, involved in
biosurfactant production (Schneiker et al. 2006; Sabirova et al. 2011; Gregson
et al. 2018). Alcanivorax genome includes putative genes for exopolysaccharides
biosynthesis, export, modification, and polymerization (Sabirova et al. 2011). Moreover, cluster for alginate biosynthesis and a number of determinants for a Type II
secretion system together with genes encoding for secretion proteins have been
identified in Marinobacter (Handley and Lloyd 2013; Mounier et al. 2018) and
Thalassolituus sp. (Morohoshi et al. 2018).
Bacteria-Degrading Aromatic Hydrocarbons
Different pattern of genes and enzymes have been described for polycyclic aromatic
hydrocarbons degradation. The widespread diffusion of polycyclic aromatic hydrocarbons in marine environment determines the presence of these compounds in
remote deep-sea sediments and hydrothermal vent sulfide minerals (Vila et al.
2015). In spite of their high toxicity, the marine bacteria can use the polycyclic
aromatic hydrocarbons as both carbon and energy sources. Table 7.1 shows some of
the strains described as polycyclic aromatic hydrocarbons-degraders. The classical
strategy for aromatic-ring cleavage, which is restricted to aerobic microorganisms,
comprises firstly the oxidation of the benzene ring to form cis-dihydrodiols catalyzed
by dioxygenase enzymes that are then dehydrogenated to form dihydroxylated
intermediates, further metabolized via catechols to water and carbon dioxide. Marine
bacteria show a wide biodiversity in metabolic pathways identified for polycyclic
aromatic hydrocarbons degradation. As an example, halophilic bacteria as
Halomonas use several downstream pathways, such as protocatechuic acid pathway,
gentisic acid pathway, and catechol pathway. Moreover, several downstream pathways to rapidly transform intermediates have been identified (Wang et al. 2018).
Cycloclasticus genus, one of the key players of polycyclic aromatic hydrocarbons
degradation in marine environment, can also degrade chlorinated derivatives of
polycyclic aromatic hydrocarbons (Dyksterhouse et al. 1995; Yakimov et al. 2007;
Yakimov et al. 2014). It has been detected in estuaries (Niepceron et al. 2010),
coastal areas (Genovese et al. 2014; Ding et al. 2017), deep-sea sediments (Wang
et al. 2008), and polar oceans (Hazen et al. 2010; Brakstad et al. 2015). Recently,
7 Biodegradation of Hydrocarbons in Marine Environment
203