Dissertation

Microbial Community Phylogeny and Function in Relation to Environment in the Norwegian Sea : a High-Throughput Community-Sequencing-Based Assessment

Carter-Gates, Michael James Alexander

2019

Overview

Significant changes to seasonal ice cover, stratification, and warming are altering the oceanic boundaries between Polar and Atlantic Water masses. The resultant increased mixing and intrusion of Atlantic Waters into the Arctic region is resulting in novel competition between extant microbial communities that drive biogeochemical cycles and underpin the food-web in these regions. However, it remains unclear how extant microbial communities will respond to these new opportunities and challenges. This work aims to provide an insight into how the bacterial and microbial eukaryotic communities present across a transect in the Norwegian Sea may be impacted by predicted future environmental change to the Arctic region through the use of Next Generation Sequencing methodologies. It is revealed that the microbial communities of the region are being partitioned into distinct assemblages that correlate with gradients of temperature and salinity. Analysis of the microbial communities from locations influenced by both Polar and Atlantic waters is used to indicate which components of the microbial communities will be selected for as these waters mix. The results of these analyses suggests the potential for the displacement of bacterial communities found at locations determined to be highly influenced by Polar Water, by bacterial communities from locations found to be primarily influenced by Atlantic Waters. This response appears consistent for all abundance fractions and constituent taxonomic groups within the bacterial community. Analysis of the eukaryotic community suggests a more complex response whereby abundant eukaryotic cold water associated species could dominate over temperate associated species, and different eukaryotic lineages display contrasting responses. Metatranscriptomes are generated for the eukaryotic community to determine the functional differences between the regional communities. Partitioning was observed which matched the gradient of Polar Water influence implying the presence of distinct genetic profiles between regional communities. Each station is observed to feature different profiles of gene expression for genes related to key ecosystem process including primary production, nutrient cycling, biogeochemical cycles, the carbon cycle and metabolic processes. However, despite some differences in the expression of functional profiles, functionality is found to be largely conserved across regional communities, suggesting increase Atlantic Water influence within the sampled region may not result in large perturbations to ecosystem functionality, despite potential changes to community composition. This study has significant implications for the vulnerability of polar associated community assemblages, which may become displaced under predicted increases of Atlantic mixing and warming within the Arctic region.

• Publisher: ProQuest Dissertations & Theses
• Subject: Biogeochemistry / Gene expression