307
Marinobacter in the presence of Corexit 9500A. Marinobacter was most sensitive
to the dispersant, with nearly 100% reduction in viability and production after exposure to Corexit in concentrations likely to be encountered during the response to the
spill (1–10 g/L).
These data suggest that the use of dispersants has the potential to reduce the
capacity of the environment to bioremediate spills, as hydrocarbon-degrading bacteria can be inhibited by chemical dispersants itself or by the BTEX compounds
released from fresh oil.
18.3 Biodegradation of Oil in the Presence of Marine Snow
in Water Phase and Benthic Zone
In the presence of high concentrations of phytoplankton, dispersant application can
induce the formation of marine snow (Van Eenennaam et al. 2016). During the
DWH oil spill, an unusual formation of marine snow was observed after the addition
of chemical dispersants to combat the oil during a phytoplankton bloom (Brooks
et al. 2015). Dispersed oil is very sticky and binds to the marine snow. Furthermore,
in the presence of mineral particles, oiled snow complexes are formed. During the
spill also a large amount of suspended solids was present due to the flushing of the
Mississippi River as a spill response (Bianchi et al. 2011; Hu et al. 2011; O'Connor
2013). When mineral particles bind to oiled marine snow particles, these complexes
become negatively buoyant and sink.
Studies have shown that microbes tend to produce more EPS as a “stress” reaction or as a natural dispersant to degrade the dispersed oil (Passow et al. 2012).
During oil spills, production of EPS could enhance the breakup of oil slicks into
droplets to induce the degradation of oil (Sohm et al. 2011). On the other hand,
more EPS production can enhance the aggregation of oil complexes, microorganisms, and other smaller particles into marine snow that settles in massive amounts
on the seabed, a phenomenon known as Marine Oil Snow Sedimentation and
Flocculent Accumulation (MOSSFA). This oiled marine snow will reduce the bioavailability of oil, and thus biodegradation will be low. Furthermore, these particles
can sink to the sea floor by gravitational settling (Sohm et al. 2011; Passow et al.
2012, Schwing et al. 2020), thus further reducing oil biodegradation.
Few studies describe the effect of marine snow on bacterial activity, as marine
snow in sufficient and reproducible quantities is not available for testing. However,
alginate, kaolin, and algae mix particles representing artificial marine snow can be
used as an approximation of real marine snow (Rahsepar et al. 2017).
Using this artificial marine snow in batch experiments, it was shown that artificial marine snow enhanced oil biodegradation in the water phase in the abundance
of dissolved oxygen (Rahsepar et al. 2017). As described in Sect. 18.2, oil biodegradation was inhibited in the presence of Corexit 9500A, due to the increased BTEX
concentrations. However, in the presence of artificial marine snow, this inhibition
was lower, probably because the toxic BTEX compounds were bound to the marine
18 Effect of Marine Snow on Microbial Oil Degradation
Marinobacter in the presence of Corexit 9500A. Marinobacter was most sensitive
to the dispersant, with nearly 100% reduction in viability and production after exposure to Corexit in concentrations likely to be encountered during the response to the
spill (1–10 g/L).
These data suggest that the use of dispersants has the potential to reduce the
capacity of the environment to bioremediate spills, as hydrocarbon-degrading bacteria can be inhibited by chemical dispersants itself or by the BTEX compounds
released from fresh oil.
18.3 Biodegradation of Oil in the Presence of Marine Snow
in Water Phase and Benthic Zone
In the presence of high concentrations of phytoplankton, dispersant application can
induce the formation of marine snow (Van Eenennaam et al. 2016). During the
DWH oil spill, an unusual formation of marine snow was observed after the addition
of chemical dispersants to combat the oil during a phytoplankton bloom (Brooks
et al. 2015). Dispersed oil is very sticky and binds to the marine snow. Furthermore,
in the presence of mineral particles, oiled snow complexes are formed. During the
spill also a large amount of suspended solids was present due to the flushing of the
Mississippi River as a spill response (Bianchi et al. 2011; Hu et al. 2011; O'Connor
2013). When mineral particles bind to oiled marine snow particles, these complexes
become negatively buoyant and sink.
Studies have shown that microbes tend to produce more EPS as a “stress” reaction or as a natural dispersant to degrade the dispersed oil (Passow et al. 2012).
During oil spills, production of EPS could enhance the breakup of oil slicks into
droplets to induce the degradation of oil (Sohm et al. 2011). On the other hand,
more EPS production can enhance the aggregation of oil complexes, microorganisms, and other smaller particles into marine snow that settles in massive amounts
on the seabed, a phenomenon known as Marine Oil Snow Sedimentation and
Flocculent Accumulation (MOSSFA). This oiled marine snow will reduce the bioavailability of oil, and thus biodegradation will be low. Furthermore, these particles
can sink to the sea floor by gravitational settling (Sohm et al. 2011; Passow et al.
2012, Schwing et al. 2020), thus further reducing oil biodegradation.
Few studies describe the effect of marine snow on bacterial activity, as marine
snow in sufficient and reproducible quantities is not available for testing. However,
alginate, kaolin, and algae mix particles representing artificial marine snow can be
used as an approximation of real marine snow (Rahsepar et al. 2017).
Using this artificial marine snow in batch experiments, it was shown that artificial marine snow enhanced oil biodegradation in the water phase in the abundance
of dissolved oxygen (Rahsepar et al. 2017). As described in Sect. 18.2, oil biodegradation was inhibited in the presence of Corexit 9500A, due to the increased BTEX
concentrations. However, in the presence of artificial marine snow, this inhibition
was lower, probably because the toxic BTEX compounds were bound to the marine
18 Effect of Marine Snow on Microbial Oil Degradation