Matching Items (43)
Description
The biological carbon pump acts as part of the global carbon cycle through the photosynthetic fixation of inorganic carbon into dissolved and particulate organic carbon by phytoplankton. Previously, the biological carbon pump was attributed to large aggregates and zooplankton fecal pellets since their size and density results in faster sinking rates, efficiently exporting organic carbon to deeper depths in the ocean. However, recent studies have indicated that small cells, known as picoplankton, contribute significantly to the formation of sinking particles. The presence of exopolymeric substances (EPS), among them sticky transparent exopolymeric particles (TEP) and proteinaceous coomassie stainable particles (CSP), serve as influential factors of export flux and aggregation. The presence of heterotrophic bacteria can also affect aggregation and sinking velocity, as seen in previous studies, and is likely attributed to their EPS and TEP production. The staining and visualization of TEP and CSP allow for the qualitative determination of these types of EPS from bacteria isolated from sinking particles collected with particle interceptor traps at various depths in the Sargasso Sea. I study the presence of TEP and CSP in particle-associated bacteria. Cultures of picocyanobacteria, consisting of xenic Synechococcus and axenic Prochlorococcus, were used to establish positive and negative controls for stained isolate analysis. Marinobacter adhaerens served as a tertiary control for an axenic culture that stains positive for TEP. I chose six isolates of bacteria isolated from sinking particles to be stained and visualized to test for the secretion of TEP and CSP. Four of the isolates stained positive for both TEP and CSP, including Pseudoalteromonas sp., Erythrobacter sp., and Marinobacter sp., while one isolate, Micrococcus sp., stained positive only for TEP, and the last isolate, another Marinobacter sp., stained positive for only CSP. These results are important in understanding the role of plankton organisms in the formation of sinking particles.
ContributorsLivar, Britni (Author) / Neuer, Susanne (Thesis director) / Cadillo-Quiroz, Hinsby (Committee member) / Cruz, Bianca (Committee member) / School of Life Sciences (Contributor, Contributor) / Barrett, The Honors College (Contributor)
Created2021-05
Description
The efficiency of the ocean’s biological carbon pump is mediated by fast-sinking particles that quickly settle out of the euphotic zone. These particles are conventionally associated with micro- (> 20 µm) sized diatoms and coccolithophorids, thought to efficiently transport carbon to depth owing to their dense mineral structures, while pico- (< 2 µm) and nanophytoplankton (2-20 µm) are considered to contribute negligibly due to their small size and low sinking speed. Despite burgeoning evidence of their export, the mechanisms behind it remain poorly understood. The objective of this dissertation is to acquire a mechanistic understanding of the contribution of pico- and nanophytoplankton to particle fluxes. I tested the hypotheses that pico- and nanophytoplankton may be exported via the following pathways: 1) physical aggregation due to the production of sticky Transparent Exopolymeric Particles (TEP), mediated by interactions with heterotrophic bacteria, 2) attachment to lithogenic minerals, and 3) repackaging by zooplankton. I found that despite the traditional view of being too small to sink, pico- and nanophytoplankton form aggregates rich in TEP, allowing cells to scavenge lithogenic minerals and thus increase their effective size and density. I discovered that interactions with heterotrophic bacteria were significant in mediating the process of aggregation by influencing the production and/or the composition of the phytoplankton-derived TEP. Bacteria differentially influenced aggregation and TEP production; some species enhanced aggregation without affecting TEP production, and vice-versa. Finally, by determining the microbial composition of sinking particles in an open-ocean site, I found pico- and nanophytoplankton significantly associated with particles sourced from crustaceous zooplankton, suggesting that their export is largely mediated by mesozooplankton.
Overall, I show that the hypothesized mechanisms of pico- and nanophytoplankton export are not mutually exclusive, but instead occur subsequently. Given the right conditions for their aggregation in the natural environment, such as interactions with aggregation-enhancing heterotrophic bacteria and/or the presence of lithogenic minerals, their cells and aggregates can escape remineralization within the euphotic zone, and thus be susceptible to grazing by mesozooplankton export within fecal pellets. The results of this dissertation provide a mechanistic framework for the contribution of pico- and nanophytoplankton to ocean particle fluxes.
ContributorsCruz, Bianca Nahir (Author) / Neuer, Susanne (Thesis advisor) / Lomas, Michael W (Committee member) / Passow, Uta (Committee member) / Cadillo-Quiroz, Hinsby (Committee member) / Arizona State University (Publisher)
Created2021
Description
The oceanic biological carbon pump is a key component of the global carbon cycle in which dissolved carbon dioxide is taken up by phytoplankton during photosynthesis, a fraction of which then sinks to depth and contributes to oceanic carbon storage. The small-celled phytoplankton (<5 µm) that dominate the phytoplankton community in oligotrophic oceans have traditionally been viewed as contributing little to export production due to their small size. However, recent studies have shown that the picocyanobacterium Synechococcus produces transparent exopolymer particles (TEP), the sticky matrix of marine aggregates, and forms abundant microaggregates (5-60 µm), which is enhanced under nutrient limited growth conditions. Whether other small phytoplankton species exude TEP and form microaggregates, and if these are enhanced under growth-limiting conditions remains to be investigated. This study aims to analyze how nutrient limitation affects TEP production and microaggregate formation of species that are found to be associated with sinking particles in the Sargasso Sea. The pico-cyanobacterium Prochlorococcus marinus (0.8 µm), the nano-diatom Minutocellus polymorphus (2 µm), and the pico-prasinophyte Ostreococcus lucimarinus (0.6 µm) were grown in axenic batch culture experiments under nutrient replete and limited conditions. It was hypothesized that phytoplankton subject to nutrient limitation will aggregate more than those under replete conditions due to an increased exudation of TEP and that Minutocellus would produce the most TEP and microaggregates while Prochlorococcus would produce the least TEP and microaggregates of the three phytoplankton groups. As hypothesized, nutrient limitation increased TEP concentration in all three species, however they were only significant in nitrogen-limited treatments of Prochlorococcus as well as nitrogen- and phosphorus-limited treatments of Minutocellus. Formation of microaggregates was significantly enhanced in Minutocellus and Ostreococcus cultures in distinct microaggregate size ranges. Minutocellus produced the most TEP per cell and aggregated at higher volume concentrations compared to Prochlorococcus and Ostreococcus. Surprisingly, Ostreococcus produced more TEP than Prochlorococcus and Minutocellus per unit cell volume. These findings show for the first time how nutrient limited conditions enhance TEP production and microaggregation of Prochlorococcus, Minutocellus, and Ostreococcus, providing a mechanism for their incorporation into larger, sinking particles and contribution to export production in oligotrophic oceans.
ContributorsShurtleff, Catrina (Author) / Neuer, Susanne (Thesis advisor) / Lomas, Michael W. (Committee member) / Garcia-Pichel, Ferran (Committee member) / Arizona State University (Publisher)
Created2022
Description
Sinking particles are important conduits of organic carbon from the euphotic zone to the deep ocean and microhabitats for diverse microbial communities, but little is known about what determines their origin and community composition. Events in the northwestern Sargasso Sea, such as winter convective mixing, summer stratification, and mesoscale (10–100 km) eddies, characteristic features of this region, affect the vertical and temporal composition and abundance of pelagic and particle-attached microorganisms. To assess the connections of the microbial communities between the euphotic zone and sinking particles, I carried out indicator and differential abundance analyses of prokaryotes and photoautotrophs based on the V4-V5 amplicons of the 16S rDNA from samples collected in the Sargasso Sea during the spring and summer of 2012. I found that gammaproteobacteria such as Pseudoalteromonas sp. and Vibrio sp., common particle-associated bacteria often linked with zooplankton, dominated the sequence libraries of the sinking particles. The analysis also revealed that members of Flavobacteria, particularly the fish pathogen Tenacibaculum sp., as well as Chloropicon sp. and Chloroparvula sp., among the smallest known green algae, were indicators taxa of sinking particles. The cryptophyte Teleaulax and the diatom Chaetoceros were overrepresented in the particle communities during both seasons. Interestingly, I also found that the large centric diatom, Rhizosolenia sp., generally rare in the oligotrophic Sargasso Sea, dominated photoautotrophic communities of sinking particles collected in the center of an anticyclonic eddy with unusual upwelling due to eddy-wind interactions. I hypothesize that the steady contribution by picophytoplankton to particle flux is punctuated by pulses of production and flux of larger-sized phytoplankton in response to episodic eddy upwelling events and can lead to higher export of particulate organic matter during the summer.
ContributorsFontánez Ortiz, Marc Alec (Author) / Neuer, Susanne (Thesis advisor) / Zhu, Qiyun (Committee member) / Trembath-Reichert, Elizabeth (Committee member) / Arizona State University (Publisher)
Created2022
Description
The biological carbon pump in the ocean is initiated by the photosynthetic fixation of atmospheric carbon dioxide into particulate or dissolved organic carbon by phytoplankton. A fraction of this organic matter sinks to depth mainly in the form of microaggregates (5-60 μm) and visible macroaggregates. These aggregates are composed of cells, minerals, and other sources of organic carbon. Exopolymeric substances (EPS) are exudated by heterotrophic bacteria and phytoplankton and may form transparent exopolymeric particles (TEP) that act as a glue-like matrix for marine aggregates. Heterotrophic bacteria have been found to influence the aggregation of phytoplankton and in some cases result in an increase in TEP production, but it is unclear if marine heterotrophic bacteria can produce TEP and how they contribute to aggregation. Pseudoalteromonas carrageenovora, Vibrio thalassae, and Marinobacter adhaerens HP15 are heterotrophic marine bacteria that were found associated with sinking particles in an oligotrophic gyre station in the subtropical North Atlantic. These bacteria were grown in axenic cultures to determine growth, TEP production, and aggregation. They were also inoculated into roller tanks used to simulate open ocean conditions to determine their ability to form macroaggregates. Treatments with added kaolinite clay simulated aeolic dust input from the Sahara. M. adhaerens HP15 had the highest TEP concentration but the lowest cell-normalized TEP production at all growth stages compared to the other bacteria. Additionally, M. adhaerens HP15 also had the lowest microaggregate formation. The cell-normalized TEP production and microaggregate formation was not significantly different between P. carrageenovora and V. thalassae. All bacteria formed visible macroaggregates in roller tanks with clay addition and exhibited high sinking velocities (150-1200 m d-1) that are comparable to those of aggregates formed by large mineral ballasted phytoplankton. Microaggregates in the clay treatments declined during incubation, indicating that they aggregated to form the macroaggregates. The findings from this study show for the first time that heterotrophic bacteria can contribute to aggregation and the export of organic carbon to depth in the ocean.
ContributorsLivar, Britni (Author) / Neuer, Susanne (Thesis advisor) / Hartnett, Hilairy (Committee member) / Cadillo-Quiroz, Hinsby (Committee member) / Arizona State University (Publisher)
Created2022
Description
Relapse after tumor dormancy is one of the leading causes of cancer recurrence that ultimately leads to patient mortality. Upon relapse, cancer manifests as metastases that are linked to almost 90% cancer related deaths. Capture of the dormant and relapsed tumor phenotypes in high-throughput will allow for rapid targeted drug discovery, development and validation. Ablation of dormant cancer will not only completely remove the cancer disease, but also will prevent any future recurrence. A novel hydrogel, Amikagel, was developed by crosslinking of aminoglycoside amikacin with a polyethylene glycol crosslinker. Aminoglycosides contain abundant amount of easily conjugable groups such as amino and hydroxyl moieties that were crosslinked to generate the hydrogel. Cancer cells formed 3D spheroidal structures that underwent near complete dormancy on Amikagel high-throughput drug discovery platform. Due to their dormant status, conventional anticancer drugs such as mitoxantrone and docetaxel that target the actively dividing tumor phenotype were found to be ineffective. Hypothesis driven rational drug discovery approaches were used to identify novel pathways that could sensitize dormant cancer cells to death. Strategies were used to further accelerate the dormant cancer cell death to save time required for the therapeutic outcome.
Amikagel’s properties were chemo-mechanically tunable and directly impacted the outcome of tumor dormancy or relapse. Exposure of dormant spheroids to weakly stiff and adhesive formulation of Amikagel resulted in significant relapse, mimicking the response to changes in extracellular matrix around dormant tumors. Relapsed cells showed significant differences in their metastatic potential compared to the cells that remained dormant after the induction of relapse. Further, the dissertation discusses the use of Amikagels as novel pDNA binding resins in microbead and monolithic formats for potential use in chromatographic purifications. High abundance of amino groups allowed their utilization as novel anion-exchange pDNA binding resins. This dissertation discusses Amikagel formulations for pDNA binding, metastatic cancer cell separation and novel drug discovery against tumor dormancy and relapse.
Amikagel’s properties were chemo-mechanically tunable and directly impacted the outcome of tumor dormancy or relapse. Exposure of dormant spheroids to weakly stiff and adhesive formulation of Amikagel resulted in significant relapse, mimicking the response to changes in extracellular matrix around dormant tumors. Relapsed cells showed significant differences in their metastatic potential compared to the cells that remained dormant after the induction of relapse. Further, the dissertation discusses the use of Amikagels as novel pDNA binding resins in microbead and monolithic formats for potential use in chromatographic purifications. High abundance of amino groups allowed their utilization as novel anion-exchange pDNA binding resins. This dissertation discusses Amikagel formulations for pDNA binding, metastatic cancer cell separation and novel drug discovery against tumor dormancy and relapse.
ContributorsGrandhi, Taraka Sai Pavan (Author) / Rege, Kaushal (Thesis advisor) / Meldrum, Deirdre R (Thesis advisor) / Stabenfeldt, Sarah (Committee member) / Caplan, Michael (Committee member) / Tian, Yanqing (Committee member) / Arizona State University (Publisher)
Created2016
Description
Plastic pollution has become a global threat to ecosystems worldwide, with microplastics now representing contaminants reported to occur in ambient air, fresh water, seawater, soils, fauna and people. Over time, larger macro-plastics are subject to weathering and fragmentation, resulting in smaller particles, termed ‘microplastics’ (measuring < 5 mm in diameter), which have been found to pollute virtually every marine and terrestrial ecosystem on the planet. This thesis explored the transfer of plastic pollutants from consumer products into the built water environment and ultimately into global aquatic and terrestrial ecosystems.
A literature review demonstrated that municipal sewage sludge produced by wastewater treatment plants around the world contains detectable quantities of microplastics. Application of sewage sludge on land was shown to represent a mechanism for transfer of microplastics from wastewater into terrestrial environments, with some countries reporting as high as 113 ± 57 microplastic particles per gram of dry sludge.
To address the notable shortcoming of inconsistent reporting practices for microplastic pollution, this thesis introduced a novel, online calculator that converts the number of plastic particles into the unambiguous metric of mass, thereby making global studies on microplastic pollution directly comparable.
This thesis concludes with an investigation of a previously unexplored and more personal source of plastic pollution, namely the disposal of single-use contact lenses and an assessment of the magnitude of this emerging source of environmental pollution. Using an online survey aimed at quantifying trends with the disposal of lenses in the US, it was discovered that 20 ± 0.8% of contact lens wearers flushed their used lenses down the drain, amounting to 44,000 ± 1,700 kg y-1 of lens dry mass discharged into US wastewater.
From the results it is concluded that conventional and medical microplastics represent a significant global source of pollution and a long-term threat to ecosystems around the world. Recommendations are provided on how to limit the entry of medical microplastics into the built water environment to limit damage to ecosystems worldwide.
A literature review demonstrated that municipal sewage sludge produced by wastewater treatment plants around the world contains detectable quantities of microplastics. Application of sewage sludge on land was shown to represent a mechanism for transfer of microplastics from wastewater into terrestrial environments, with some countries reporting as high as 113 ± 57 microplastic particles per gram of dry sludge.
To address the notable shortcoming of inconsistent reporting practices for microplastic pollution, this thesis introduced a novel, online calculator that converts the number of plastic particles into the unambiguous metric of mass, thereby making global studies on microplastic pollution directly comparable.
This thesis concludes with an investigation of a previously unexplored and more personal source of plastic pollution, namely the disposal of single-use contact lenses and an assessment of the magnitude of this emerging source of environmental pollution. Using an online survey aimed at quantifying trends with the disposal of lenses in the US, it was discovered that 20 ± 0.8% of contact lens wearers flushed their used lenses down the drain, amounting to 44,000 ± 1,700 kg y-1 of lens dry mass discharged into US wastewater.
From the results it is concluded that conventional and medical microplastics represent a significant global source of pollution and a long-term threat to ecosystems around the world. Recommendations are provided on how to limit the entry of medical microplastics into the built water environment to limit damage to ecosystems worldwide.
ContributorsRolsky, Charles (Author) / Halden, Rolf (Thesis advisor) / Green, Matthew (Committee member) / Neuer, Susanne (Committee member) / Polidoro, Beth (Committee member) / Smith, Andrew (Committee member) / Arizona State University (Publisher)
Created2020
Description
One of the most pronounced issues affecting the management of fisheries today is bycatch, or the unintentional capture of non-target species of marine life. Bycatch has proven to be detrimental for many species, including marine megafauna and pelagic fishes. One method of reducing bycatch is illuminated gillnets, which involves utilizing the differences in biological visual capabilities and behaviors between species of bycatch and target fish catch. To date, all studies conducted on the effects of net illumination on bycatch and target fish catch have been conducted at night. In this study, the effects of net illumination on bycatch, target fish catch, and market value during both night and day periods at Baja California Sur, Mexico were compared. It was found that i) net illumination is effective (p < 0.05) at reducing bycatch of finfish during the day and at night, ii) net illumination at night is more effective (p < 0.05) at reducing bycatch for elasmobranchs, Humboldt squid, and aggregate bycatch than during the day, iii) time of day did not have an effect (p > 0.05) on sea turtle bycatch, and iv) net illumination did not significantly (p > 0.05)affect target catch or market value at night or during the day. These results suggest that net illumination may be an effective strategy for reducing finfish bycatch in fisheries that operate during the day or across 24 h periods, and is especially effective for reducing elasmobranch, Humboldt squid, and total bycatch biomass at night.
ContributorsDenton, Kyli Elise (Author) / Senko, Jesse (Thesis advisor) / Neuer, Susanne (Thesis advisor) / Pratt, Stephen (Committee member) / Arizona State University (Publisher)
Created2021
Description
Coral reefs are diverse marine ecosystems, where reef building corals provide both the structure of the habitat as well as the primary production through their symbiotic algae, and alongside algae living on the reef itself, are the basis of the food web of the reef. In this way, coral reefs are the ocean's "forests" and are estimated to support 25% of all marine species. However, due to the large size of a coral reef, the relative inaccessibility and the reliance on in situ surveying methods, our current understanding of reefs is spatially limited. Understanding coral reefs from a more spatially complete perspective will offer insight into the ecological factors that contribute to coral reef vitality. This has become a priority in recent years due to the rapid decline of coral reefs caused by mass bleaching. Despite this urgency, being able to assess the entirety of a coral reef is physically difficult and this obstacle has not yet been overcome. However, similar difficulties have been addressed in terrestrial ecosystems by using remote sensing methods, which apply hyperspectral imaging to assess large areas of primary producers at high spatial resolutions. Adapting this method of remote spectral sensing to assess coral reefs has been suggested, but in order to quantify primary production via hyper spectral imaging, light-use efficiencies (LUEs) of coral reef communities need to be known. LUEs are estimations of the rate of carbon fixation compared to incident absorbed light. Here, I experimentally determine LUEs and report on several parameters related to LUE, namely net productivity, respiration, and light absorbance for the main primary producers in coral reefs surrounding Bermuda, which consist of algae and coral communities. The derived LUE values fall within typical ranges for LUEs of terrestrial ecosystems, with LUE values for coral averaging 0.022 ± 0.002 mol O2 mol photons-1 day-1 at a water flow rate of 17.5 ± 2 cm s^(-1) and 0.049 ± 0.011 mol O2 mol photons-1 day-1 at a flow rate of 32 ± 4 cm s^(-1) LUE values for algae averaged 0.0335 ± 0.0048 mol O2 mol photons-1 day-1 at a flow rate of 17.5 ± 2 cm s^(-1). These values allow insight into coral reef productivity and opens the door for future remote sensing applications.
ContributorsFlesher, David A (Author) / Neuer, Susanne (Thesis director) / Redding, Kevin (Committee member) / School of Molecular Sciences (Contributor) / School of Life Sciences (Contributor) / Barrett, The Honors College (Contributor)
Created2019-05
Description
Prochlorococcus marinus (MED4), a genus of marine picocyanobacteria that proliferates in open oligotrophic ocean, is one of the most abundant photosynthetic microbes in the world, estimated to contribute up to 10% of the ocean’s primary production. The productivity of these microorganisms is controlled by macronutrient availability in the surface waters. The ratio of macronutrients in the ocean was defined, by Alfred Redfield, as an elemental ratio of 106C:16N:1P. However, the C:N:P ratio varies based on region, season, temperature and irradiance, as well as the composition of the primary producers. In oligotrophic gyres, these nutrient ratios are elevated from the Redfield stoichiometry, but whether this ratio exerts influence on the growth rate of the organism has not been investigated. Elemental stoichiometry of available nutrients can affect the aggregation of organic carbon and exportation of the particles to the ocean depths. The purpose of this study was to investigate the effects of nutrient limitation on aggregation and transparent exopolymeric particle (TEP) production which aids in aggregation. My findings suggested that nutrient limitation reduces TEP production and does not increase aggregate volume concentration. With continued warming, certain regions of the ocean will become more oligotrophic, which further decreases the nutrient supply available for Prochlorococcus. My research shows that this could lead to decreased exportation of organic carbon matter to the depths of the sea.
ContributorsRoy, Kevin Thomas (Author) / Neuer, Susanne (Thesis director) / Cadillo-Quiroz, Hinsby (Committee member) / Cruz, Bianca (Committee member) / Department of Psychology (Contributor) / School of Molecular Sciences (Contributor) / School of Life Sciences (Contributor) / Barrett, The Honors College (Contributor)
Created2019-05