While dissolved organic nitrogen (DON) plays a central role in global ocean N cycling, little is known about specific DON components. To address one aspect of this, investigators from Kent State University and the University of Georgia will examine polyamines, an under-studied microbially-produced DON component. They hypothehesize that, despite the low concentrations of these N-rich compounds, free polyamines have an important role in microbial ecology. To test this hypothesis, the investigators will examine the concentration, flux and fate of dissolved polyamines and dissolved amino acids at nearshore and open ocean sites using various chemical analyses. The composition of bacterial assemblages and of genes involved in polyamine utilization will also be determined using state-of-the-art molecular techniques. By integrating biogeochemical and molecular approaches, and linking functional genomics of plankton assemblages to material fluxes, the work will improve the understanding of the fate and dynamics of DON in marine environments, and the importance of polyamines as sources of C and N. This collaborative project will enhance inter-institution partnerships, and train graduate students while also reaching out to under-represented and promising first- and second-year undergraduate and high school students. The students will be involved with research opportunities, summer internships, and other activities.
Dissolved organic nitrogen represents a significant pool of labile nitrogen in marine systems. However, our knowledge on marine DON transformation is based on a small proportion of compounds that are presumably important, such as amino acids. Polyamines represent another group of marine DON and, like amino acids, they are widely distributed in marine systems. In the cells of phytoplankton (the major DON source) and in seawater, polyamines have similar concentration gradients as amino acids. Recent genetic studies also showed a high abundance of polyamine-related genes in the genomes, metagenomes and metaproteomes of marine bacteria. These suggest that polyamines may be another critical component of marine DON cycle. The aim of the project was to test this hypothesis. We performed several field studies and collected samples from stations that have high, medium and low supply of nutrients in various regions, including the South Atlantic Bight and the Gulf of Mexico. We found that polyamines were indeed rapidly turned over by marine microbes at rates that were similar to amino acids. The concentrations of polyamines and amino acids showed significant spatial and temporal variations; typically the former had much lower values. Consequently, the measured fluxes of polyamines were generally lower than fluxes of amino acids. However, at times, polyamine concentrations were as high as amino acids and the fluxes of these two types of DON were comparable. In addition, consistent with previous findings, polyamine concentrations were correlated with primary productivity. Therefore, at algal bloom conditions, polyamine turnover may be significant to DON flux. Incubation experiments were performed to examine genes, metagenomes and metatranscriptomes that were involved in polyamine transformation. Our results suggest that polyamines were widely used by a diverse group of marine bacteria with Roseobacter and SAR11 bacterial lineages as the most important polyamine transformers. This collaborative project involved scientists from two institutions and offered interdisciplinary training to graduate students from both places (two PhD students and one master student). This project also provided training for 8 under-represented and promising first- and second-year undergraduate students in basic microbiology lab skills. In addition, the PIs worked with the Upward Bound Math/Science Center and reached under-represented (African American, Hispanic, Native American, and Pacific Islander) students from low-income families who have interest in pursuing a science major in college. The results of the study have been published in 4 peer-reviewed papers and two other manuscripts have been submitted and are in review. Three more manuscripts are in preparation for publication.
