Thesis (M.S.)--Rutgers University, 2008. / "Graduate Program in Oceanography." Includes bibliographical references (p. 29-32).

Thesis (Ph. D.)--Biology, Georgia Institute of Technology, 2005. / Thomas DiChristina, Committee Member ; Patricia Sobecky, Committee Member ; Christopher Klausmeier, Committee Member ; Douglas G. Capone, Committee Member ; Montoya, Joseph P., Committee Chair ; Samantha Joye, Committee Member. Includes bibliographical references.

Abstract This research investigated the spatial and temporal distributions of Trichodesmium spp. and Richelia intracellularis in the South China Sea. The surveys covered the period from July 2000 to July 2002. A total of eight cruises, including spring, summer and fall were conducted. The sampling stations located between 18~22o N and 115~122 o E , over the continental shelf, the slope, and the basin of the northern South China Sea. Trichodesmium biomass was higher in summer and fall than spring. There was no significant difference in biomass among shelf , slope and basin. The averaged biomass was 69

Thesis (Ph. D.)--Oregon State University, 2007. / Printout. Includes bibliographical references (leaves 139-148). Also available on the World Wide Web.

University, Diss., 2005--Kiel.

The colonial, N2 fixing cyanobacterium Trichodesmium is a keystone species in oligotrophic ocean ecosystems. Trichodesmium is responsible for approximately 50% of the total biologically fixed N2 in the ocean, and this “new” nitrogen fuels primary productivity and the amount of carbon sequestered by the ocean. Trichodesmium does not exist in isolation. Colonies occur ubiquitously with an assemblage of epibiotic microorganisms that are distinct from planktonic microbes and modulated across environments, yet the implications of this relationship have not been explored. In this thesis, the ecology, physiology, and potential geochemical impact of interactions within the Trichodesmium host-microbiome system were examined across three different oligotrophic ocean environments. First, to establish the metabolic diversity contributed by the microbiome to Trichodesmium consortia, a whole community metagenomic sequencing approach was used across a transect the western North Atlantic. This study demonstrated that the microbiome contributes a large amount of unique functional potential and is modulated across a geochemical gradient. In the following study, metatranscriptomics was used to show that such metabolic potential in Trichodesmium and the microbiome was expressed and modulated across the environment. Colonies were sampled in the western tropical South Pacific and gene expression dynamics indicated co-limitation by iron and phosphorus, and revealed a mechanism for phosphate reduction by Trichodesmium and subsequent utilization by the microbiome. These activities were verified with phosphate reduction rate measurements and indicated cryptic phosphorus cycling within colonies. Next, the suite of potential physiological interactions between host and microbiome was assessed with metatranscriptome sequencing on high frequency samples of Trichodesmium colonies from the North Pacific subtropical gyre. Synchronized day-night gene expression periodicity between consortia members indicated tightly linked metabolisms. The functional annotations of these synchronous genes indicated intra-consortia cycling of nitrogen, phosphorus and iron, as well as a microbiome dependence on Trichodesmium-derived cobalamin—interactions that could alter the transfer of these resources to the surrounding water column. In the final study, the effect of the microbiome on Trichodesmium N2 fixation was assessed. Using colonies obtained from the North Atlantic, activity in the microbiome was selectively modified using quorum sensing acyl homoserine lactone cell-cell signaling, a mechanism that Trichodesmium itself does not possess. These experiments indicated that the microbiome has the potential to increase or decrease Trichodesmium N2 fixation to a degree that rivals the effects of alterations in nutrient concentration, but at a more rapid rate. In all, the research presented in this thesis demonstrates the integral importance of the microbiome to Trichodesmium physiology and ecology, highlighting the importance of an unexplored facet of marine microbial systems that likely influences the biogeochemistry of the planet.

Trichodesmium is a globally significant marine diazotroph responsible for supplying new nitrogen to the oligotrophic regions in which it is found. Though it has been studied for decades, our understanding of the ways in which environmental factors can affect its nitrogen fixation rate remains limited. A continuous culture of Trichodesmium was established in which steady state growth and nitrogen fixation were maintained at dilution rates ranging from 0.27 to 0.67 d-1. Our results clearly show that, as growth rate increased, biomass decreased linearly and nitrogen fixation rate increased linearly. C:N:P ratios remained constant over the range of growth rates studied, suggesting a tight coupling between macronutrient uptake and the maintenance of balanced growth at steady state. We used cultures at steady state to determine the impact of nitrate exposure and uptake on nitrogen fixation. Nitrate inhibits nitrogen fixation by up to 70% in a concentration-dependent manner at initial nitrate concentrations less than 10?? Nitrate uptake accounted for as much as 86% of total N uptake and, at initial nitrate concentrations greater than 2.5 ??more than made up for the observed inhibition of nitrogen fixation. A field study of this diazotroph shows that nitrogen fixation scales with light intensity from a maximum at 50% surface irradiance. Estimated areal nitrogen fixation rates in the Gulf of Mexico, based on vertical abundance profiles and the relationship between nitrogen fixation and surface irradiance, are comparable to measurements made in other oligotrophic regions. Stable isotopic composition of the particulate organic matter and the zooplankton confirms that Trichodesmium nitrogen and carbon are moving into the food chain and are important to higher trophic levels. As much as 60% of the zooplankton carbon was derived from Trichodesmium. Our work established that this diazotroph is ecologically important in the water column of the Gulf of Mexico, with important implications for nitrogen and carbon cycling. Findings from our field and culture studies can be added to models used to quantify the importance of Trichodesmium nitrogen fixation on an oceanic scale.

This research studied the iron deficient condition of the nitrogen-fixing filamentous cyanobacteria Trichodesmium in neighboring oligotrophic northern South China Sea and upstream Kuroshio. The iron deficiency was detected by the immunocytochemical analysis of the expression of iron deficiency induced protein A (IdiA), a protein translated by Trichodesmium cells under iron deficiency. IdiA expression rate (percentage of cells stained by IdiA antiserum in total cells) was used to represent the iron deficiency status. Trichodesmium samples were collected in four cruises by net-towing or bottle-sampling in the Kuroshio and the shelf, slope and basin of the South China Sea between December 2008 and May 2010, representing three seasons: Spring (CR899 and CR1455), Summer (CR910) and Winter (CR886). The results showed that the IdiA expression rates vaied greatly among the stations in the South China Sea. Iron supplies from various sources decreased the IdiA expressions rates (i.e., less iron deficient). These sources include: (1) Mixing from deep layer, such as in the continental shelf of the South China Sea in which internal wave occured, and upwelling occurred in the continental slope; (2) Mixing at some stations in the South China Sea basin from the input of river dischange, especially in the events after typhoon. During these events, stations with lower surface water salinities usually implied lower IdiA expression rates. In contrast, the basin station that were high in salinities showed high IdiA expression rates, higher than the rates in the Kuroshio. These stations generally had strongly stratified water coulumn, and therefore might limit the ward mixing of deep water. The incubation experiment conducted showed that 24 hours after adding iron, Trichodesmium IdiA expression rates were significantly decreased. The Kuroshio, with its water column stratification weaker than South China Sea, the IdiA expression rates were lower than the basin stations in South China Sea, and positively relatied with the stratification index, indicating that deep advection may be the main source of iron. In the incubation experiments in Kuroshio, the expression rates did not significantly differ with iron or without iron addition. The IdiA expression rates in both regions were not related to flux of atmospheric dust, indicating the input from the dust was not key point to decrease iron deficiency of Tricodesmium in this two region. This study shows that iron deficient condition of diazotrophic Trichodesmium in South China Sea and upstream Kuroshio were related to vertical mixing and horizontal discharge, but not dust flux. This study is first time to apply immunocytochemical analysis on field experiments to explain iron deficiency in the ocean.

This investigation tested the hypothesis that iron, as a micronutrient, will affect proteins in Trichodesmium and therefore affect nitrogen fixation. Changes in proteins that are a result of iron enrichment were compared to naturally occuring diel changes. Alterations in the iron protein of nitrogenase were compared to nitrogen fixation rates using the acetylene reduction technique. The observed changes in proteins were compared in Trichodesmium colonies from the Caribbean Sea and the Sargasso Sea. Trichodesmium colonies were monitored for protein and iron content over a diel period on two cruises. The changes in protein and iron content in Trichodesmium colonies were variable but at times showed a cyclic diel pattern. Changes in protein bands on SDS-PAGE showed consistent changes in the banding pattern of a low molecular weight protein that responded to iron nutrition and time of day (Elardo and Rueter 1990). These changes were similar to changes m the iron protein of nitrogenase which also responded to changes associated with iron nutrition and time of day (Elardo 1991 ). Trichodesmium appear to alter certain proteins which appear as changes in banding patterns in response to environmental factors such as nutrients, temperature and light. My research shows that the pattern of modification of the iron protein of nitrogenase differs in colonies from the Caribbean Sea compared to those from the Sargasso Sea (Elardo 1991). The Caribbean Sea population in February had a clear pattern of active and inactive forms (day vs. night) of the enzyme. The Sargasso Sea population of Trichodesmium spp. had both forms of the enzyme at all times of the day during April and May when NO3 - is present in the euphotic zone due to recent mixing. These differences between the two populations may be due to different environmental conditions since the Caribbean Sea is permanently stratified, warmer and nutrient-depleted throughout the year. The Sargasso Sea undergoes seasonal breakdown of the thermocline during winter months, resulting in an injection of nitrate from deeper water, and minimum temperatures of 18oC.

Upwelling, atmospheric nitrogen (N2) fixation by cyanobacteria, and freshwater inputs from the Mississippi River system have been shown to stimulate new production by alleviating nitrogen (N) limitation in the northern Gulf of Mexico (GoM). Stable carbon (delta13C) and nitrogen (delta15N) isotopes were used to investigate whether these sources are utilized differentially by coastal and marine pelagic food webs. Particulate organic matter (POM), Trichodesmium, and zooplankton were collected from the Mississippi River plume and Loop Current (LC) which were detected using remote sensing data. Stable isotope values were used to separate coastal and marine water masses and environmental data (salinity, nutrient and pigment concentrations) allowed me to relate variability to the degree of freshwater influence. Published food web data from these two environments were then assessed to establish whether isotopic baseline shifts observed in our data occur at an ecosystem level. Isotope values of the POM and zooplankton were found to be significantly different between coastal and marine water masses. This was not the case for Trichodesmium whose isotope values were not significantly different between the two water masses. We found that marine water masses (sal > 35) exhibited silicate concentrations, cyanobacterial pigments and DIN: P that suggest an increased abundance of diazotrophs. In contrast, coastal water masses (sal < 35) exhibited increased diatom pigments and molar C:N indicating terrestrial sources fuel phytoplankton production. When published food web data were compared, we found producer and consumer delta15N values were enriched in the coastal compared to the marine environments. This work suggests that differences in delta15N values within my data set and published data reflect a shift in the use of biologically available N where higher trophic levels are sustained by diazotrophic activity in marine environments versus those supported by terrestrial sources in coastal ones. Food webs that have been constructed without considering Trichodesmium as a significant source of organic matter in the GoM should be reconsidered. By re-evaluating published data, this research gives insight into the early life ecology of larval fishes and works to help answer questions about the structure and function of pelagic food webs.