Award: OCE-1924554

Metals such as iron and copper have a role as essential micronutrients due to their role within metalloenzymes that catalyze chemical reactions. Within the mesopelagic ocean, microbes use metalloenzymes to conduct essential chemical reactions to transform key nitrogen transformations. This project studied theEastern Tropical Pacific Ocean using the new biogeochemical autonomous underwater vehicle (AUV) Clio that enables high-resolution vertical sampling for biochemical and microbial measurements by filtering large volumes of seawater to collect biological and chemical samples. Three topics were investigated: (1) the influence of environmental gradients in oxygen and trace metals on microbial metalloenzyme distribution, (2) limitation of the nitrite oxidation reaction by iron availability in the upper mesopelagic through an inability to complete biosynthesis of the microbial protein nitrite oxidoreductase, and (3) if nitrite-oxidizing bacteria increase their metalloenzyme requirements at low oxygen, impacting the distribution of both dissolved and particulate metals within oxygen minimum zones. To study these questions a full depth microbial biogeochemistry ocean section was sampled for genomics, transcriptomics, proteomics, metabolomics and biogeochemistry, the latter including dissolved metals nutrients. Using the AUV Clio simultaneously with over-the-side wire-based activities (Mclane pumps, trace metal and standard rosettes) significant station time efficiency was achieved, collecting more higher quality samples while also saving at least 10 days of ship time. This expedition collected over 400 omics and biogeochemistry sample stations (unique station / depth environments), quadrupling our previous attempts for interdisciplinary sampling efficiency. The sampling approach holds promise for future BioGeoSCAPES ocean sampling expeditions. Incubation experiments were conducted with iron additions in an ammonia rich shallow water environment. Both chlorophyll increase and ammonia decreases were observed in the experiment across biological triplicates, implying that ammonia oxidation was iron limited through an inability to synthesize the iron and copper containing ammonia monooxygenase enzyme, concurrent with phytoplankton inability to grow due to an inability to have sufficient iron nutrition for photosynthesis.This kind of dual limitation of processes is novel and proteomic data will help verify these hypotheses about simultaneous nutrient stress in two distinct functional microbial communities. Iron and copper stable isotope uptake studies were also conducted and showed significant mesopelagic uptake, implying an important biological sink for metals in these low oxygen waters. The results of this study are contributing data and educational resources for the Ocean Protein Portal for use in classroom based research activities. Last Modified: 04/09/2024 Submitted by: MakASaito