Award: OCE-1130495

Almost half of the biomass in the ocean biota is found in bacteria. The bacterial carbon and nitrogen ultimately sustain all higher levels of production in the ocean, yet many aspects of the links from bacteria to higher trophic levels are still unknown. The objective of this study was to elucidate the links between marine bacteria and common marine zooplankton, specifically copepods. Copepods are abundant mesozooplanktonic crustaceans that form an important link in marine food webs, serving as a major food source for many marine fishes and mammals. The focus of this study was to investigate copepod-associated bacterial communities from the subtropical open ocean, and coastal, temperate waters of the North Atlantic Ocean. The composition and activity of these specific bacterial communities were characterized via several molecular, microbiological, and biogeochemical techniques. The approaches included high throughput DNA sequencing for characterization of overall microbial community composition, approaches targeting microbial functional protein coding genes involved in specific microbial nutrient transformation pathways, gene expression analysis, measurements with stable isotope tracers, and bacterial isolation to monocultures and genome sequencing. The data demonstrate that the microbial community associated with copepods (copepod microbiome) is dynamic, with high spatial and temporal variability. The results also showed that variability in bacterial community composition seen in copepods is linked with seasonality and it correlates with copepod feeding status. By studying individuals with voided guts and investigating gut data from seasonally collected samples, it was shown that while part of the microbiome originates or is induced by copepod food, copepods retain some bacterial associations that are consistently present and thus can be considered their core microbiome. This core microbiome has similarities across different geographic regions but includes a relatively high number of different types of bacteria. Described functions of the bacterial isolates and copepod core microbiome include certain microbially-mediated biogeochemical transformations in the marine nitrogen and carbon cycle that are unlikely if the bacteria exhibit a free-living lifestyle in the water column, and suggest some marine bacteria specialize living in association with copepods. The data demonstrated that certain bacteria from the microbiome are specialized to withstand or thrive under conditions that are lacking oxygen. Overall the results show that the copepod environment provides a unique microenvironment in the marine water column that selects and enriches for specific bacterial communities. With the high abundance of copepods in the marine environment, contribution of these epibiotic and endobiotic bacterial communities should play an important role in marine production, marine food webs, and specific transformations of elements in marine biogeochemical cycles. The project involved international collaborations with scientists from four countries outside the United States. This collaborative research that leveraged a wide range of expertise in these laboratories, resulted in key contributions toward the research outcomes. This project provided research infrastructure, training, and opportunities to engage with national and international scientific community for several graduate and undergraduate students, and overall, aspects of the research were incorporated to undergraduate class curricula. The award contributed to five M.S. theses and one Ph.D. dissertation. Data has been shared via submission to sequence databases and the Biological and Chemical Oceanography Data Management Office database. The results of the award have been disseminated via publication of several peer-reviewed manuscripts, presentations in national and international conferences, and invited talks. Last Modified: 01/25/2017 Submitted by: Pia Moisander