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carbon degradation genes as a proxy for hydrocarbon degradation potential, it was
concluded that while alkane degradation was not affected, a significant decrease
was observed in aromatic hydrocarbon degradation potential at increasing pressure. While growth declined with increasing pressure, no differences in microbial
community composition were observed across pressure treatments. Community
analysis of the incubations showed that known psychrotolerant hydrocarbondegrading bacteria affiliated with Oleispira antarctica dominated the communities at all pressures (Marietou et al. 2018). Similarly, Fasca et al. (2018) observed
minor effects of pressure (22 MPa) on the microbial community of microcosms
prepared with seawater collected off the coast of Brazil from an oil extraction
platform.
Pressure is thought to impact hydrocarbon biodegradation through effects on
solubility, especially for gaseous hydrocarbons. For example, a number of studies
have demonstrated the effect of methane partial pressure, i.e., concentration of
dissolved methane, on rates of anaerobic methane oxidation (Kallmeyer and
Boetius 2004; Deusner et al. 2009; Zhang et al. 2010; Bowles et al. 2011; Timmers
et al. 2015). In sediments from a number of cold seep sites including the
Mississippi Canyon in the Gulf of Mexico, Bowles et al. (2011) observed 6–10
times higher rates of anaerobic methane oxidation at 10 MPa compared to atmospheric pressure. In agreement with Bowles et al., Timmers et al. (2015) reported
that high methane partial pressure stimulated initial anaerobic methane oxidation
activity of sediment from Eckernförde Bay, Germany. Total pressure and methane
concentration appeared to epistatically influence the rate of anaerobic methane
oxidation (Bowles et al. 2011). Therefore, total pressure and methane concentration should be considered independently in the investigation of pressure effects on
methanotrophy.
State-of-the-art technology, which can independently control the total pressure
and methane concentration, can be used to separate out the effects of solubility
(Deusner et al. 2009; Bowles et al. 2011; Schedler et al. 2014; Valladares Juárez et al.
2015; Case et al. 2017). High-pressure reactors were constructed at the Hamburg
University of Technology in collaboration with industry partners (Technikservice
A. Meyer, Eurotechnica, and PreSens, Germany) (Fig. 7.3). Pressurization is achieved
with inert gas, enabling independent control of total pressure of the system and partial pressure of another gas of interest, for example, oxygen for aerobic biodegradation and gaseous hydrocarbons such as methane for methanotrophy studies. The
system permits a higher biodegradation extent than conventional high-pressure reactors without a headspace, allowing detailed investigation of hydrocarbon degradation
while avoiding toxicity associated with increased oxygen partial pressure. The
reactors are equipped with an oxygen sensor for continuous monitoring as a proxy
for biodegradation. Additionally, a new optical system has been developed based
on an optical flow cell for near infrared (NIR) spectroscopic analysis of gas mixtures at high pressure (Norton et al. 2014). The optical system was directly mounted
onto a high-pressure reactor. Thus, gaseous hydrocarbon biodegradation can be
monitored at high pressure online in real time via removal of the gas from the headspace while bypassing the subsampling of high- pressure gas mixtures for off-line
analysis (Fig. 7.3).
J. E. Kostka et al.
carbon degradation genes as a proxy for hydrocarbon degradation potential, it was
concluded that while alkane degradation was not affected, a significant decrease
was observed in aromatic hydrocarbon degradation potential at increasing pressure. While growth declined with increasing pressure, no differences in microbial
community composition were observed across pressure treatments. Community
analysis of the incubations showed that known psychrotolerant hydrocarbondegrading bacteria affiliated with Oleispira antarctica dominated the communities at all pressures (Marietou et al. 2018). Similarly, Fasca et al. (2018) observed
minor effects of pressure (22 MPa) on the microbial community of microcosms
prepared with seawater collected off the coast of Brazil from an oil extraction
platform.
Pressure is thought to impact hydrocarbon biodegradation through effects on
solubility, especially for gaseous hydrocarbons. For example, a number of studies
have demonstrated the effect of methane partial pressure, i.e., concentration of
dissolved methane, on rates of anaerobic methane oxidation (Kallmeyer and
Boetius 2004; Deusner et al. 2009; Zhang et al. 2010; Bowles et al. 2011; Timmers
et al. 2015). In sediments from a number of cold seep sites including the
Mississippi Canyon in the Gulf of Mexico, Bowles et al. (2011) observed 6–10
times higher rates of anaerobic methane oxidation at 10 MPa compared to atmospheric pressure. In agreement with Bowles et al., Timmers et al. (2015) reported
that high methane partial pressure stimulated initial anaerobic methane oxidation
activity of sediment from Eckernförde Bay, Germany. Total pressure and methane
concentration appeared to epistatically influence the rate of anaerobic methane
oxidation (Bowles et al. 2011). Therefore, total pressure and methane concentration should be considered independently in the investigation of pressure effects on
methanotrophy.
State-of-the-art technology, which can independently control the total pressure
and methane concentration, can be used to separate out the effects of solubility
(Deusner et al. 2009; Bowles et al. 2011; Schedler et al. 2014; Valladares Juárez et al.
2015; Case et al. 2017). High-pressure reactors were constructed at the Hamburg
University of Technology in collaboration with industry partners (Technikservice
A. Meyer, Eurotechnica, and PreSens, Germany) (Fig. 7.3). Pressurization is achieved
with inert gas, enabling independent control of total pressure of the system and partial pressure of another gas of interest, for example, oxygen for aerobic biodegradation and gaseous hydrocarbons such as methane for methanotrophy studies. The
system permits a higher biodegradation extent than conventional high-pressure reactors without a headspace, allowing detailed investigation of hydrocarbon degradation
while avoiding toxicity associated with increased oxygen partial pressure. The
reactors are equipped with an oxygen sensor for continuous monitoring as a proxy
for biodegradation. Additionally, a new optical system has been developed based
on an optical flow cell for near infrared (NIR) spectroscopic analysis of gas mixtures at high pressure (Norton et al. 2014). The optical system was directly mounted
onto a high-pressure reactor. Thus, gaseous hydrocarbon biodegradation can be
monitored at high pressure online in real time via removal of the gas from the headspace while bypassing the subsampling of high- pressure gas mixtures for off-line
analysis (Fig. 7.3).
J. E. Kostka et al.