Alkyl nitrates from the oceans significantly affect tropospheric ozone concentration. However, not all sources of oceanic alkyl nitrates have been identified. A few studies have demonstrated a photochemical source of oceanic alkyl nitrates but to date, limited, if any other sources have been identified. For this reason, a scientist from Loyola College proposes to investigate the biological source of alkyl nitrates from marine diatoms. Specifically, the research goals of the project would be the following: (1) determine if cultures of phytoplankton produce alkyl nitrates under 'normal' growth conditions and the rates of production of alkyl nitrates in the cultures; (2) determine if there are specific factors such as light, nutrients, and temperature that influence alkyl nitrate formation; and (3) determine if adding triggers or inhibitors of nitric oxide production in phytoplankton cause changes in alkyl nitrate production. The proposed work will improve our overall understanding of the potential sources of oceanic alkyl nitrates and the factors that may control these sources, as well as lead to new considerations in biogeochemistry as to what role phytoplankton may play in the nitrogen cycle specifically with regard to reactive nitrogen.
As regards broader impacts, it is anticipated that results from the research will be incorporated into Biochemistry and Instrumental Analysis classes taught by the researcher. Two undergraduate students will be supported and trained as part of this project. These students will learn about culturing techniques and how to operate a gas chromatograph-mass spectrometer.
This project focused on determining if alkyl nitrates may be formed by biological activity in the oceans. Alkyl nitrates are a trace gas that is present in the oceans and subsequently transferred to the atmosphere. Alkyl nitrates from the oceans have previously been shown to have a significant impact on ozone and hydroxyl radicals in the lower atmosphere. We do not know how alkyl nitrates are produced in the oceans and this project specifically aimed to determine if marine microbiota in the oceans may produce alkyl nitrates. Previous work has shown that alkyl nitrates can be produced in water from chemical reactions of nitric oxide (NO) and organic peroxy radicals (ROO) that are initiated by light. Algae are known to form nitric oxide during normal growth (via nitrate/nitrite reductase) and as a stress reaction (via nitric oxide synthase). We hypothesized that the formation of nitric oxide from algae could lead to alkyl nitrate production. This project initially focused on production of alkyl nitrates from 2 different species of diatoms and 1 species of cyanobacteria all of which are unicellular marine algae. Over the course of this project we observed that cultures of marine algae actually did not produce a lot of alkyl nitrates unless there were non-photosynthetic bacteria present with the algae. The levels produced by the marine algae without the bacteria were not high enough to account for surface ocean observations of alkyl nitrates. When bacteria were present the concentrations increased by as much as 100x compared to the bacteria free cultures. As a result of this observation we began to work with combinations of marine algae with a known strain of bacteria as well an unknown strain of bacteria that contaminated our experiments. Through these experiments we learned that the unknown strain resulted in greater formation of alkyl nitrates than both the algae alone and with the known strain. In addition, adding the amino acid arginine to our experiment resulted in higher concentration of alkyl nitrates in the cultures containing the unknown bacteria strain(s). This observation is significant because it demonstrates that 1) alkyl nitrates can and are biologically produced by micro-organisms and 2) provided evidence that nitric oxide synthase may play a role in biological alkyl nitrate production – our original hypothesis - may be correct. More significantly, this project helped to further our understanding of how gases that are important to atmospheric chemistry are produced by microbiota in the marine ecosystem. Many important atmospheric gases are produced by marine micro-organisms and this project has confirmed that alkyl nitrates are produced by micro-organisms. Further work is planned to determine alkyl nitrate production using only the bacteria strains as well as to work with filtrate from the cultures to determine if alkyl nitrates can be produced from the chemicals produced by the organisms without the physical presence of the bacteria or algae. In addition to the scientific contribution – a major outcome of this project was the training and mentoring of 8 undergraduate chemistry and biology students (63% women) who worked on this project. Prior to working on this project, these students had not previously been exposed to or learned about marine and atmospheric chemistry or analytical chemistry. They also did not know the important of marine microbiota to atmospheric chemistry or to the global ecosystem. As a result of this project, most of the students prepared presentations and papers on their work and 4 out of 8 attended national meeting of the American Geophysical Union and/or the American Chemical Society. Three of the students who have graduated have gone on to PhD programs in chemistry and 4 are either enrolled in or in the process of applying to professional schools.
