116
populations followed by a longer persistence of the PAH-degrading genus
Cycloclasticus (Yang et al. 2016). Although reports are contradictory and based on
few samples (<10), sedimentary microbial communities may have returned to baseline conditions within 1 year following the spill (Yang et al. 2016; Liu et al. 2017).
The inferred rates of recovery suggested by these studies exceed estimates of decay
rates in contaminating hydrocarbons. This is potentially due to a dilution effect
from sedimented natural organic matter, whereby few contaminated oil particles
settling to the seafloor result in low to moderately contaminated sediments (Bagby
et al. 2017).
7.4 Effect of High Pressure on Microbially Mediated
Hydrocarbon Degradation
Organisms with optimal growth rates above 0.1 MPa (atmospheric pressure) are
defined as piezophiles (from the Greek “piezo,” meaning “to press”) (Yayanos
1995) and span a wide range of bacterial and archaeal lineages (Horikoshi 1998).
While our understanding of the mechanisms by which piezophiles adapt and thrive
at high pressures is limited, available evidence points to adjustments in gene replication, protein expression, membrane chemistry, production of osmolytes (Simonato
et al. 2006), and antioxidant defense response (Xie et al. 2018). The most wellcharacterized response of piezophiles to pressure is their ability to increase the proportion of unsaturated fatty acids in their membrane lipids at increasing pressure in
order to preserve membrane fluidity (Simonato et al. 2006).
Almost 70 years ago, Zobell and Johnson (1949) reported that sulfate-reducing
bacteria isolated from several thousand meters deep terrestrial oil wells were metabolically more active at elevated pressures of 40 MPa or 60 MPa (Zobell and Johnson
1949). Subsequently, hydrocarbon-degrading microorganisms have been isolated
from numerous deep sea environments, thus suggesting that hydrocarbon degradation can proceed at increasing pressure (Tapilatu et al. 2010a, b). As offshore deep
sea drilling operations are expected to increase in the future, understanding the
effect of pressure on microbial hydrocarbon degradation is becoming increasingly
important.
7.4.1 Ex Situ Incubations of Enriched Seawater
and Sediments
The earliest reports on the effects of pressure on microbial hydrocarbon degradation
were published in the late 1970s (Schwarz et al. 1974). Schwarz et al. (1974)
provided the first evidence that the indigenous microbial community was able to
degrade hydrocarbons at high pressure using respiration to CO 2 as a proxy
J. E. Kostka et al.
populations followed by a longer persistence of the PAH-degrading genus
Cycloclasticus (Yang et al. 2016). Although reports are contradictory and based on
few samples (<10), sedimentary microbial communities may have returned to baseline conditions within 1 year following the spill (Yang et al. 2016; Liu et al. 2017).
The inferred rates of recovery suggested by these studies exceed estimates of decay
rates in contaminating hydrocarbons. This is potentially due to a dilution effect
from sedimented natural organic matter, whereby few contaminated oil particles
settling to the seafloor result in low to moderately contaminated sediments (Bagby
et al. 2017).
7.4 Effect of High Pressure on Microbially Mediated
Hydrocarbon Degradation
Organisms with optimal growth rates above 0.1 MPa (atmospheric pressure) are
defined as piezophiles (from the Greek “piezo,” meaning “to press”) (Yayanos
1995) and span a wide range of bacterial and archaeal lineages (Horikoshi 1998).
While our understanding of the mechanisms by which piezophiles adapt and thrive
at high pressures is limited, available evidence points to adjustments in gene replication, protein expression, membrane chemistry, production of osmolytes (Simonato
et al. 2006), and antioxidant defense response (Xie et al. 2018). The most wellcharacterized response of piezophiles to pressure is their ability to increase the proportion of unsaturated fatty acids in their membrane lipids at increasing pressure in
order to preserve membrane fluidity (Simonato et al. 2006).
Almost 70 years ago, Zobell and Johnson (1949) reported that sulfate-reducing
bacteria isolated from several thousand meters deep terrestrial oil wells were metabolically more active at elevated pressures of 40 MPa or 60 MPa (Zobell and Johnson
1949). Subsequently, hydrocarbon-degrading microorganisms have been isolated
from numerous deep sea environments, thus suggesting that hydrocarbon degradation can proceed at increasing pressure (Tapilatu et al. 2010a, b). As offshore deep
sea drilling operations are expected to increase in the future, understanding the
effect of pressure on microbial hydrocarbon degradation is becoming increasingly
important.
7.4.1 Ex Situ Incubations of Enriched Seawater
and Sediments
The earliest reports on the effects of pressure on microbial hydrocarbon degradation
were published in the late 1970s (Schwarz et al. 1974). Schwarz et al. (1974)
provided the first evidence that the indigenous microbial community was able to
degrade hydrocarbons at high pressure using respiration to CO 2 as a proxy
J. E. Kostka et al.