Response of microalgal-bacterial consortia to ocean acidification and crude oil pollution

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.