Made possible by our awesome collaborators at Georgia Aquarium!
Burns AS, Padilla CC, Pratte ZA, Gilde K, Regensburger M, Hall E, Dove ADM, Stewart FJ. 2018. Broad phylogenetic diversity associated with nitrogen loss through sulfur oxidation in a large public marine aquarium. Applied and Environmental Microbiology. In press.
manuscript posted online 10 August 2018, doi:10.1128/AEM.01250-18
Denitrification by sulfur-oxidizing bacteria is an effective nitrate removal strategy in engineered aquatic systems. However, the community taxonomic and metabolic diversity of sulfur-driven denitrification (SDN) systems, as well as the relationship between nitrate removal and SDN community structure, remains underexplored. This is particularly true for SDN reactors applied to marine aquaria, despite increasing use of this technology to supplement filtration. We applied 16S rRNA gene, metagenomic, and metatranscriptomic analysis to explore the microbial basis of SDN reactors operating on Georgia Aquarium’sOcean Voyager, the largest indoor closed-system seawater exhibit in the United States. The exhibit’s two SDN systems vary in water retention time and nitrate removal efficiency. The systems also support significantly different microbial communities. These communities contain canonical SDN bacteria, including a strain related to Thiobacillus thioparus that dominates the system with higher water retention time and nitrate removal, but is effectively absent from the other system. Both systems contain a wide diversity of other microbes whose metagenome-assembled genomes contain genes of SDN metabolism. These include hundreds of strains of the epsilonproteobacterium Sulfurimonas, as well as gammaproteobacterial sulfur oxidizers of the Thiotrichales and Chromatiales, and a relative of Sedimenticola thiotaurini with complete denitrification potential. SDN genes are transcribed and the taxonomic richness of the transcript pool varies markedly among enzymatic steps, with some steps dominated by transcripts from non-canonical SDN taxa. These results indicate complex and variable SDN communities that may involve chemical dependencies among taxa, as well as the potential for altering community structure to optimize nitrate removal.
Engineered aquatic systems such as aquaria and aquaculture facilities have large societal value. Ensuring the health of animals in these systems requires understanding how microorganisms contribute to chemical cycling and waste removal. Focusing on the largest seawater aquarium in the US, we explore the microbial communities in specialized reactors designed to remove excess nitrogen through the metabolic activity of sulfur-consuming microbes. We show that the diversity of microbes in these reactors is both high, and highly variable, with distinct community types associated with significant differences in nitrogen removal rate. We also show that the genes encoding the metabolic steps of nitrogen removal are distributed broadly throughout community members, suggesting that the chemical transformations in this system are likely a result of microbes relying on other microbes. These results provide a framework for future studies exploring the contributions of different community members, both in waste removal and in structuring microbial biodiversity.