111
environment are available (Joye et al. 2014; Joye 2015), which makes it extremely
difficult to assess the magnitude and efficiency of oil biodegradation. Methane
oxidation rates were measured rather extensively, and available data suggests that
microbial methane oxidation rates were sluggish and ineffective (Valentine et al.
2010; Crespo-Medina et al. 2014).
Estimates of hydrocarbon oxidation rates derived from deepwater oxygen anomalies support the notion that hydrocarbon degradation rates were inefficient; e.g.,
measured hydrocarbon loads in the deepwater plumes could have driven more
extensive oxygen depletion, had there been efficient oxidation (Joye et al. 2011).
Given the paucity of field data on hydrocarbon degradation rates (i.e., direct measurements), it is extremely difficult to constrain the fate of oil and gas discharged
during the DWH spill (Joye 2015). Best estimates of water column hydrocarbon
oxidation suggest that between 43% and 61% of the discharged hydrocarbons were
oxidized (Joye 2015). In the case of a future offshore marine oil spill, it is imperative that cutting-edge approaches be employed to constrain hydrocarbon oxidation
rates across the water column (e.g., Sibert et al. 2017).
7.2.2 Microbial Community Changes During the Spill,
Pre- spill, and Post-spill
The “baseline” microbial community in the Gulf water column contains a significant
fraction of hydrocarbon-degrading microorganisms, mostly affiliated with the
Gammaproteobacteria (Kleindienst et al. 2015c). This community is perpetuated by
widespread, diffuse natural seepage of hydrocarbons into the water column (Joye
et al. 2014). Prior to the oil spill, Gammaproteobacteria accounted for up to ~23% of
SSU rRNA gene sequence reads, and about 7% of those sequences affiliated specifically with hydrocarbon-degrading microorganisms (Yang et al. 2016; Kleindienst
et al. 2015a). The metabolic requirements of oil-degrading microbes vary, but early in
the incident within the deepwater plume, Gammaproteobacteria became highly
enriched, increasing in abundance to account for 43–98% of sequence reads. The vast
majority of the organisms that bloomed were hydrocarbon degraders.
The most abundant Gammaproteobacteria early in the event were
Oceanospirillales, Colwellia, and Cycloclasticus (Hazen et al. 2010; Mason et al.
2012). Methylotrophs and methanotrophs were less abundant, but Methylophaga
reached levels up to 7% of all sequence reads by September 2010. The Bacteroidetes
also increased in abundance late in the incident. The Methylophaga and Bacteroidetes
are likely secondary consumers of intermediate metabolites instead of primary
degraders of hydrocarbons. The ability of gammaproteobacterial oil degraders to
respond rapidly to oil infusion underscores their critical environmental role.
Even though their population biomass is constrained under “background” conditions,
sufficient metabolic diversity and functional efficiency exist to allow a rapid
response to increased substrate availability.
7 Biodegradation of Petroleum Hydrocarbons in the Deep Sea
environment are available (Joye et al. 2014; Joye 2015), which makes it extremely
difficult to assess the magnitude and efficiency of oil biodegradation. Methane
oxidation rates were measured rather extensively, and available data suggests that
microbial methane oxidation rates were sluggish and ineffective (Valentine et al.
2010; Crespo-Medina et al. 2014).
Estimates of hydrocarbon oxidation rates derived from deepwater oxygen anomalies support the notion that hydrocarbon degradation rates were inefficient; e.g.,
measured hydrocarbon loads in the deepwater plumes could have driven more
extensive oxygen depletion, had there been efficient oxidation (Joye et al. 2011).
Given the paucity of field data on hydrocarbon degradation rates (i.e., direct measurements), it is extremely difficult to constrain the fate of oil and gas discharged
during the DWH spill (Joye 2015). Best estimates of water column hydrocarbon
oxidation suggest that between 43% and 61% of the discharged hydrocarbons were
oxidized (Joye 2015). In the case of a future offshore marine oil spill, it is imperative that cutting-edge approaches be employed to constrain hydrocarbon oxidation
rates across the water column (e.g., Sibert et al. 2017).
7.2.2 Microbial Community Changes During the Spill,
Pre- spill, and Post-spill
The “baseline” microbial community in the Gulf water column contains a significant
fraction of hydrocarbon-degrading microorganisms, mostly affiliated with the
Gammaproteobacteria (Kleindienst et al. 2015c). This community is perpetuated by
widespread, diffuse natural seepage of hydrocarbons into the water column (Joye
et al. 2014). Prior to the oil spill, Gammaproteobacteria accounted for up to ~23% of
SSU rRNA gene sequence reads, and about 7% of those sequences affiliated specifically with hydrocarbon-degrading microorganisms (Yang et al. 2016; Kleindienst
et al. 2015a). The metabolic requirements of oil-degrading microbes vary, but early in
the incident within the deepwater plume, Gammaproteobacteria became highly
enriched, increasing in abundance to account for 43–98% of sequence reads. The vast
majority of the organisms that bloomed were hydrocarbon degraders.
The most abundant Gammaproteobacteria early in the event were
Oceanospirillales, Colwellia, and Cycloclasticus (Hazen et al. 2010; Mason et al.
2012). Methylotrophs and methanotrophs were less abundant, but Methylophaga
reached levels up to 7% of all sequence reads by September 2010. The Bacteroidetes
also increased in abundance late in the incident. The Methylophaga and Bacteroidetes
are likely secondary consumers of intermediate metabolites instead of primary
degraders of hydrocarbons. The ability of gammaproteobacterial oil degraders to
respond rapidly to oil infusion underscores their critical environmental role.
Even though their population biomass is constrained under “background” conditions,
sufficient metabolic diversity and functional efficiency exist to allow a rapid
response to increased substrate availability.
7 Biodegradation of Petroleum Hydrocarbons in the Deep Sea