Evaluating microbial community dynamics with regards to the metabolic denitrification pathway in the Saanich Inlet

Abstract

The climate crisis has driven the expansion of oxygen minimum zones (OMZ) in oceans worldwide. OMZs disproportionally effect oceanic biological nitrogen loss, contributing to a global 50%, while only comprising of 7% of total volume.   As such, it is becoming increasingly important to understand the effects of deoxygenation on marine microbial communities. These microorganisms play a major role in nutrient cycling by catalyzing geochemical reactions that maintain the levels of nutrients required to sustain marine life. However, the growing prevalence of OMZs is known to influence the microbial composition of marine environments, thereby causing an imbalance in the reactions such as ones pertaining to the nitrogen cycle. This study aims to address this concern by identifying microbial taxa at various depths of the Saanich Inlet, an OMZ in British Columbia, Canada that serves as a model ecosystem for global deoxygenation. Using the TreeSAPP metagenomic pipeline, microbial communities from the Saanich Inlet containing the denitrification genes napA, narI, nirK, norB, and nosZ were taxonomically classified at the phylum level. Gene abundance and alpha diversity was quantified and compared at the metagenomic and metatranscriptomic levels.  Metagenomic and metatranscriptomic insights revealed that many species that were capable of executing reactions in the nitrogen cycle, often did not perform these reactions Additionally, a regression model was created that depicts a high degree of association between diversity of taxa that contain a specific denitrification gene, differences in ‘omic type, and energy of a denitrification metabolic reaction. This analysis provides insight into the roles of microbial communities involved in the denitrification pathway, and can be applied to broader OMZs to better understand the implications of deoxygenation on global nutrient cycling.