112
The majority of studies used patterns of SSU rRNA gene sequence abundance to
infer patterns of metabolism (Kessler et al. 2011; Dubinsky et al. 2013). While some
microbial metabolic clades vary in ways that could suggest changes in substrate
abundance (Dubinsky et al. 2013), a metagenomic approach allows for specific
microbial populations to be linked to specific metabolic pathways of hydrocarbon
degradation (Rodriguez-R et al. 2015). As noted previously, the rates of hydrocarbon degradation in the water column are debated. Camilli et al. (2010) suggest very
slow rates of hydrocarbon metabolism, while Hazen et al. (2010) suggest rapid turnover. Since degradation rates of major hydrocarbon classes were not determined
directly under in situ (temperature and pressure) conditions and were instead
inferred or estimated using indirect approaches, assessments of structure-function
relationships are problematic.
7.2.3 The Influence of Dispersants on Microbial Community
and Biodegradation
The impact of chemical dispersants on rates of hydrocarbon degradation is hotly
debated, and the literature contains conflicting reports (Kleindienst et al. 2015a, b;
Ferguson et al. 2017; Joye et al. 2016; Rahsepar et al. 2016). While dispersants
increase the amount of oil partitioned into the aqueous phase, it is unclear whether
dispersants increase oil biodegradation rates, which is a requirement for their efficacy. A consistent body of evidence documenting dispersant-mediated stimulation
of oil degradation under realistic environmental conditions is lacking. Thus, a great
deal of this variability likely stems from the different experimental approaches that
were employed, such as addition of nutrients to samples that would otherwise be
nutrient limited. Given the inconsistency in available reports, it is imperative to
develop new approaches that allow investigations to be carried out under conditions
that closely match those in the environment. The oil used in the experiment also
plays an important role and may explain discrepancies between published reports.
For example, few studies matched DWH field deepwater plume dissolved dispersant (DOSS) and oil concentrations (as TPH) (e.g., Kleindienst et al. 2015a), but
when conditions mimicked in situ conditions, no stimulation of oil biodegradation
by dispersant addition was observed.
7.3 Biodegradation in Sediments
A unique aspect of the DWH spill is that it injected large amounts of oil into the
deep sea, 1.5 km below the sea surface, with approximately 14% of the oil deposited
onto the sediments (Chanton et al. 2012; Valentine et al. 2014; Bagby et al. 2017;
J. E. Kostka et al.
The majority of studies used patterns of SSU rRNA gene sequence abundance to
infer patterns of metabolism (Kessler et al. 2011; Dubinsky et al. 2013). While some
microbial metabolic clades vary in ways that could suggest changes in substrate
abundance (Dubinsky et al. 2013), a metagenomic approach allows for specific
microbial populations to be linked to specific metabolic pathways of hydrocarbon
degradation (Rodriguez-R et al. 2015). As noted previously, the rates of hydrocarbon degradation in the water column are debated. Camilli et al. (2010) suggest very
slow rates of hydrocarbon metabolism, while Hazen et al. (2010) suggest rapid turnover. Since degradation rates of major hydrocarbon classes were not determined
directly under in situ (temperature and pressure) conditions and were instead
inferred or estimated using indirect approaches, assessments of structure-function
relationships are problematic.
7.2.3 The Influence of Dispersants on Microbial Community
and Biodegradation
The impact of chemical dispersants on rates of hydrocarbon degradation is hotly
debated, and the literature contains conflicting reports (Kleindienst et al. 2015a, b;
Ferguson et al. 2017; Joye et al. 2016; Rahsepar et al. 2016). While dispersants
increase the amount of oil partitioned into the aqueous phase, it is unclear whether
dispersants increase oil biodegradation rates, which is a requirement for their efficacy. A consistent body of evidence documenting dispersant-mediated stimulation
of oil degradation under realistic environmental conditions is lacking. Thus, a great
deal of this variability likely stems from the different experimental approaches that
were employed, such as addition of nutrients to samples that would otherwise be
nutrient limited. Given the inconsistency in available reports, it is imperative to
develop new approaches that allow investigations to be carried out under conditions
that closely match those in the environment. The oil used in the experiment also
plays an important role and may explain discrepancies between published reports.
For example, few studies matched DWH field deepwater plume dissolved dispersant (DOSS) and oil concentrations (as TPH) (e.g., Kleindienst et al. 2015a), but
when conditions mimicked in situ conditions, no stimulation of oil biodegradation
by dispersant addition was observed.
7.3 Biodegradation in Sediments
A unique aspect of the DWH spill is that it injected large amounts of oil into the
deep sea, 1.5 km below the sea surface, with approximately 14% of the oil deposited
onto the sediments (Chanton et al. 2012; Valentine et al. 2014; Bagby et al. 2017;
J. E. Kostka et al.