| dc.description.abstract | Hydrocarbon-degrading bacteria play a crucial role in the recovery of marine systems in
the event of an oil spill, and associate with various species of eukaryotic phytoplankton
in the ocean. There is a paucity of knowledge to explain the relationship between these
types of bacteria living associated with microalgae, and their collective response to oil
spills in future ocean acidification (OA) conditions has not been studied to date. This
thesis presents the first investigation that aims to understand the response of these
organisms under future atmospheric CO2 concentration (750ppm) and crude oil spills.
Research was conducted on laboratory cultures of Emiliania huxleyi and natural
community assemblage of subarctic surface seawater. Using high-throughput analysis of
16S rRNA sequencing, previously described key hydrocarbon degrading bacteria such as
Marinobacter, Alcanivorax, and Oleispira were detected associated with microalgae. The
response of bacterial community varied from being 1) negatively affected by OA and oil
enrichment, 2) negatively affected by OA, but positively affected by oil enrichment under
projected ocean acidification conditions, or 3) positively affected by OA and oil
enrichment. Marinobacter and Methylobacterium were negatively affected by OA, which
exacerbated the response of E. huxleyi to crude oil exposure. However, biodegradation of
crude oil was not significantly affected. Marinobacter was also negatively impacted in
the natural microbial community samples. Polaribacter was negatively affected in ocean
acidification conditions and when exposed to crude oil enrichment. Colwellia was
negatively impacted by OA but thrived during exposure to both crude oil and future ocean
acidification conditions. Sulfitobacter and Psychrobacter was positively impacted by OA
and oil pollution. Despite detection of hydrocarbonoclastic bacteria in natural community
assemblage, their relative abundance in the bacterial community did not increase as
expected after oil enrichment. Furthermore, no biodegradation of crude oil was detected
in microcosms with natural microbial community. Highly abundant taxa in both spring
and fall communities from the northeast Atlantic, such as Colwellia and members of
families Rhodobacteraceae and Halomonadaceae, and the class Gammaproteobacteria,
were persistent even when exposed to both stressors. In the event of an oil spill by the
end of the century, OA favours selection of persistent and resilient bacteria that will
outcompete hydrocarbonoclastic bacteria, thus delaying biodegradation and recovery
from crude oil pollution in a future ocean. | en |
