Matching Items (4)
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- All Subjects: Cyanobacteria
- Creators: Cadillo-Quiroz, Hinsby
Description
Nitrous oxide (N2O) is a major contributor to the greenhouse effect and to stratospheric ozone depletion. In soils, nitrogen reduction is performed by biotic and abiotic processes, including microbial denitrification and chemical denitrification. Chemical denitrification, or chemodenitrification, is the abiotic step-wise reduction of nitrate (NO3-), nitrite (NO2-), or nitric oxide (NO) to N2O in anoxic environments, with high turnover rates particularly in acidic soils. Chemodenitrification was identified in various environments, but the mechanism is still not understood. In this study, the factors influencing abiotic reduction of NO2- to N2O in acidic tropical peat soil are examined. These factors include pH, organic matter content, and dissolved ferrous iron. Anoxic peat soil from sites located in the Peruvian Amazon was used for incubations. The results show that peat soil (pH ~4.5) appears to reduce NO2- more quickly in the presence of lower pH and higher Fe(II) concentrations. NO2- is completely reduced in excess Fe(II), and Fe(II) is completely oxidized in excess NO2-, providing evidence for the proposed mechanism of chemodenitrification. In addition, first order reaction rate constants kFe(II) and kNO2- were calculated using concentration measurements over 4 hours, to test for the hypothesized reaction rate relationships kFe(II): kFe(II) kFe(II)~NO2- > kFe(II)>NO2- and kNO2-: kFe(II)NO2-. The NO2- k values followed the anticipated pattern, although the Fe(II) k value data was inconclusive. Organic material may also play a role in NO2- reduction through chemodenitrification, and future experimentation will test this possibility. How and to what extent the pH and the concentrations of organic matter and Fe(II) affect the kinetic rate of chemodenitrification will lend insight into the N2O production potential of natural tropical peatlands.
ContributorsTylor, Kaitlyn Marie (Author) / Cadillo-Quiroz, Hinsby (Thesis director) / Day, Thomas (Committee member) / School of Life Sciences (Contributor) / Barrett, The Honors College (Contributor)
Created2016-05
Description
“Extremophile” is used to describe life that has adapted to extreme conditions and the conditions they live in are often used to understand the limits of life. In locations with low precipitation and high solar radiation, photosynthetic cyanobacteria can colonize the underside of quartz fragments, forming ‘hypoliths.’ The quartz provides protection against wind, reduces solar radiation, and slows the rate of evaporation following infrequent rain or fog events. In most desert systems, vascular plants are the main primary producers. However, hypoliths might play a key role in carbon fixation in hyperarid deserts that are mostly devoid of vegetation. I investigated hypolith distribution and carbon fixation at six sites along a rainfall and fog gradient in the central Namib Desert in Namibia. I used line point intersect transects to assess ground cover (bare soil, colonized quartz fragment, non-colonized quartz fragment, non-quartz rock, grass, or lichen) at each site. Additionally, at each site I selected 12 hypoliths and measured cyanobacteria colonization on quartz and measured CO2 flux of hypoliths at five of the six sites.
Ground cover was fairly similar among sites, with bare ground > non-colonized quartz fragments > colonized quartz fragments > non-quartz rocks. Grass was present only at the site with the highest mean annual precipitation (MAP) where it accounted for 1% of ground cover. Lichens were present only at the lowest MAP site, where they accounted for 30% of ground cover. The proportion of quartz fragments colonized generally increased with MAP, from 5.9% of soil covered by colonized hypoliths at the most costal (lowest MAP) site, to 18.7% at the most inland (highest MAP) site. There was CO2 uptake from most hypoliths measured, with net carbon uptake rates ranging from 0.3 to 6.4 μmol m-2 s-1 on well hydrated hypoliths. These carbon flux values are similar to previous work in the Mojave Desert. Our results suggest that hypoliths might play a key role in the fixation of organic carbon in hyperarid ecosystems where quartz fragments are abundant, with MAP constraining hypolith abundance. A better understanding of these extremophiles and the niche they fill could give an understanding of how microbial life might exist in extraterrestrial environments similar to hyperarid deserts.
Ground cover was fairly similar among sites, with bare ground > non-colonized quartz fragments > colonized quartz fragments > non-quartz rocks. Grass was present only at the site with the highest mean annual precipitation (MAP) where it accounted for 1% of ground cover. Lichens were present only at the lowest MAP site, where they accounted for 30% of ground cover. The proportion of quartz fragments colonized generally increased with MAP, from 5.9% of soil covered by colonized hypoliths at the most costal (lowest MAP) site, to 18.7% at the most inland (highest MAP) site. There was CO2 uptake from most hypoliths measured, with net carbon uptake rates ranging from 0.3 to 6.4 μmol m-2 s-1 on well hydrated hypoliths. These carbon flux values are similar to previous work in the Mojave Desert. Our results suggest that hypoliths might play a key role in the fixation of organic carbon in hyperarid ecosystems where quartz fragments are abundant, with MAP constraining hypolith abundance. A better understanding of these extremophiles and the niche they fill could give an understanding of how microbial life might exist in extraterrestrial environments similar to hyperarid deserts.
ContributorsMonus, Brittney Daniel (Author) / Throop, Heather (Thesis director) / Hall, Sharon (Committee member) / Cadillo-Quiroz, Hinsby (Committee member) / School of Life Sciences (Contributor) / School of Earth and Space Exploration (Contributor) / Barrett, The Honors College (Contributor)
Created2016-12
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
Description
The changes in marine ecological conditions brought on by warming and stratification of the oceans have radically shifted many marine environments around the globe. This project aimed to better characterize the aggregation behavior of the abundant picocyanobacterium Prochlorococcus marinus, which is hypothesized to dominate over other phytoplankton as the primary autotroph in increasingly warmer and nutrient poor oceans. This aggregation, believed to be mediated through the secretion of sticky Transparent Exopolymeric Substances (TEP), might be key for Prochlorococcus to sink throughout the ocean and serve as a source of carbon to other communities within its environment. Considering the relatively low concentration of TEP secreted by Prochlorococcus when on its own, this study explored the synergistic effect that heterotrophic bacteria and inorganic minerals in the surrounding seawater may have on the aggregation of P. marinus. This was done by inoculating P. marinus and the model heterotroph Marinobacter adhaerens HP15 individually and mixed in cylindrical roller tanks with the addition of ballasting clay minerals into roller tanks to simulate constant sinking for 7 days. The aggregates which formed after rolling were quantified and their sinking velocities and excess densities were measured. Our results indicate that the most numerous and densest aggregates formed when Prochlorococcus was in the presence of both M. adhaerens and kaolinite clay particles. I will discuss how methodology, particularly cell number, may play a role in the enhanced aggregation that I found when Prochlorococcus was cultured together with the Marinobacter.
ContributorsAouad, Samer Ghassan (Author) / Neuer, Susanne (Thesis director) / Cadillo-Quiroz, Hinsby (Committee member) / Cruz, Bianca (Committee member) / School of Life Sciences (Contributor) / Barrett, The Honors College (Contributor)
Created2020-05