UnderPressure - Avaliando o impacto de metais na diversidade microbiana e ciclo do azoto no mar profundo

The overall objective of this project is to evaluate the impacts of metal exposure on deep-sea microbial diversity and nitrogen cycling. To achieve this goal, we propose the following specific objectives: OBJECTIVE 1 - Investigate baseline microbial diversity patterns and N cycling potential in deep-sea sediments. Before assessing the metal impacts on deep-sea microbial diversity and N cycling potential, one must first obtain an overarching baseline of microbial community structure, which is absent for this ecosystem. A recent global survey of open ocean metagenomes has shown that the deep benthic realm is vastly underexplored, when compared to the pelagic environment (20). In this project, we aim to expand this analysis by querying different public sequence databases and by adding several metagenomes collected by us in previous expeditions. Alpha- and beta-diversity patterns, as well as N cycling potential, will be described across different basins and deep-sea habitats (massive sulfides, abyssal plains, and seamounts) to identity currently unknown biogeographic patterns and habitat heterogeneity. OBJECTIVE 2 - Investigate the impacts of metal exposure on microbial diversity and N cycling potential of deep-sea sediment communities. The second major knowledge gap addressed by this project is trying to predict the impacts of metals potentially released during deep-sea mining activities on the diversity and functioning of microbial communities. Even though previous studies of metal toxicity in other environments could provide environmental analogues (12, 21, 22), the unique nature and special environmental conditions of the deep-sea (i.e. light, temperature, pressure) substantially limits extrapolations. Shipboard experiments with freshly collected deep-sea samples, such as the ones being used in this project, are a robust alternative to particularly challenging field experiments in the deep-sea. By using metagenomic and metatranscriptomic analyses, we will explore the potential long- and short-term effects of metal exposure on deep-sea microbial communities. OBJECTIVE 3 - Evaluate the metal impacts on the transcriptomic and N-cycling pathways of model deep-sea bacterial isolates. Our recent research has shown that Cd exposure can alter N2O physiology and associated gene expression in deep-sea isolates (19). Other preliminary data from our lab (in prep.) have also showed us that these responses vary drastically between isolates and between metals. Different resistance phenotypes and N-pathway prioritization may be critical to explain differential responses, but these are widely unknown for deep-sea isolates. In this project, we will explore the whole transcriptome profile of various deep-sea isolates under exposure to different metals. Hypothetically, bacteria may be able to resist metal contamination due to the expression of resistance genes, but their metabolic potential to process nitrogen species may be compromised. Testing this “fitness-cost” concept will contribute to unveil novel toxicity thresholds of microbial processes in the deep-sea. Our research objectives reflect a combined approach that spans global baseline knowledge (objective 1) as well as ecological (objective 2) and physiological responses (objective 3), which we believe can generate important advances to a widely unknown ecosystem where the reality of human exploitation is about to change.