7.2 Microbial Hydrocarbon Biodegradation
7.2.1 Bacterial Hydrocarbons Biodegradation
Several marine ecological niches, both extreme and conventional, host hydrocarbondegrading bacteria. The biogeography of hydrocarbon-degrading bacteria has been
continuously updating and has demonstrated that they are widely distributed around
the world (Oliveira et al. 2017), including in the polar region (Crisafi et al. 2016),
hydrothermal vents (He et al. 2015), deep-sea (Liu et al. 2019), and hypersaline
environments (Fathepure 2014). Coastal zones disturbed by frequent oil input
together with chronically oil-polluted sites (ports, the surroundings of refineries,
mining marine sites) show an increase of hydrocarbon-degrading bacteria relative
density (Denaro et al. 2005; Yakimov et al. 2005; Yakimov et al. 2007; Crisafi et al.
2016; Zhang et al. 2017; McFarlin et al. 2018). The potential of hydrocarbonsdegrading bacteria has been known for decades. Zobell (1946) perceived an interesting opportunity on the use of hydrocarbon-degrading bacteria for the clean-up of
oil-polluted areas. Cutting-edge omics technologies have allowed to deeply investigate structural and functional features of natural bacterial communities, together
with genome of bacterial strains, their genes, enzymes, metabolites, and degradation
pathway and network as crucial components of biodegradation processes (Bargiela
et al. 2015; Zhang et al. 2019). Biodegradation of petroleum depends on the nature
and on the amount of the hydrocarbons, which determine their availability to bacteria
(Cooney et al. 1985; Chaudhry et al. 2005; Rojo 2009; Beskoski et al. 2011; Chandra
et al. 2013). In particular, the susceptibility of hydrocarbons to microbial degradation
is generally ranked as follows: linear alkanes > branched alkanes > low-molecularweight alkyl aromatics > monoaromatics > cyclic alkanes > polyaromatics
> asphaltenes (Atlas 1981; Leahy and Colwell 1990; Atlas and Bragg 2009; Varjani
2017). Hydrocarbon degradation can be influenced by the bioavailability of nutrients
such as nitrogen and phosphorous (Bootpathy 2000; Rahman et al. 2006; Varjani
et al. 2015). Temperature, pH, and oxygen can also limit the efficiency of the process
(Atlas 1991; McKew et al. 2007; Chandra et al. 2013; Taffi et al. 2014). Moreover,
high amount of organic matter associated with long-term hydrocarbon contamination can reduce the bioavailability of the pollutant (Santos et al. 2003). Among biotic
factors affecting oilbiodegradation, predation is considered as a positive event
because it creates a nutritional loop, but at the same time may cause a decrease in
the number of hydrocarbon-degrading bacteria in comparison to a predator-less
condition (Bootpathy 2000).
7.2.2 Bacteria-Degrading Aliphatic Hydrocarbons
Although 75 different bacterial genera have been so far described as hydrocarbonsdegraders (Prince 2005), little is known on marine strains, likely due to their known
7 Biodegradation of Hydrocarbons in Marine Environment
199
7.2.1 Bacterial Hydrocarbons Biodegradation
Several marine ecological niches, both extreme and conventional, host hydrocarbondegrading bacteria. The biogeography of hydrocarbon-degrading bacteria has been
continuously updating and has demonstrated that they are widely distributed around
the world (Oliveira et al. 2017), including in the polar region (Crisafi et al. 2016),
hydrothermal vents (He et al. 2015), deep-sea (Liu et al. 2019), and hypersaline
environments (Fathepure 2014). Coastal zones disturbed by frequent oil input
together with chronically oil-polluted sites (ports, the surroundings of refineries,
mining marine sites) show an increase of hydrocarbon-degrading bacteria relative
density (Denaro et al. 2005; Yakimov et al. 2005; Yakimov et al. 2007; Crisafi et al.
2016; Zhang et al. 2017; McFarlin et al. 2018). The potential of hydrocarbonsdegrading bacteria has been known for decades. Zobell (1946) perceived an interesting opportunity on the use of hydrocarbon-degrading bacteria for the clean-up of
oil-polluted areas. Cutting-edge omics technologies have allowed to deeply investigate structural and functional features of natural bacterial communities, together
with genome of bacterial strains, their genes, enzymes, metabolites, and degradation
pathway and network as crucial components of biodegradation processes (Bargiela
et al. 2015; Zhang et al. 2019). Biodegradation of petroleum depends on the nature
and on the amount of the hydrocarbons, which determine their availability to bacteria
(Cooney et al. 1985; Chaudhry et al. 2005; Rojo 2009; Beskoski et al. 2011; Chandra
et al. 2013). In particular, the susceptibility of hydrocarbons to microbial degradation
is generally ranked as follows: linear alkanes > branched alkanes > low-molecularweight alkyl aromatics > monoaromatics > cyclic alkanes > polyaromatics
> asphaltenes (Atlas 1981; Leahy and Colwell 1990; Atlas and Bragg 2009; Varjani
2017). Hydrocarbon degradation can be influenced by the bioavailability of nutrients
such as nitrogen and phosphorous (Bootpathy 2000; Rahman et al. 2006; Varjani
et al. 2015). Temperature, pH, and oxygen can also limit the efficiency of the process
(Atlas 1991; McKew et al. 2007; Chandra et al. 2013; Taffi et al. 2014). Moreover,
high amount of organic matter associated with long-term hydrocarbon contamination can reduce the bioavailability of the pollutant (Santos et al. 2003). Among biotic
factors affecting oilbiodegradation, predation is considered as a positive event
because it creates a nutritional loop, but at the same time may cause a decrease in
the number of hydrocarbon-degrading bacteria in comparison to a predator-less
condition (Bootpathy 2000).
7.2.2 Bacteria-Degrading Aliphatic Hydrocarbons
Although 75 different bacterial genera have been so far described as hydrocarbonsdegraders (Prince 2005), little is known on marine strains, likely due to their known
7 Biodegradation of Hydrocarbons in Marine Environment
199