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Methanogens are methane-producing archaea that play a major role in the global carbon cycle. However, despite their importance, the community dynamics of these organisms have not been thoroughly characterized or modeled. In the majority of methanogenesis models, the communities are approximated as a chemical reaction or divided into two populations based on the most common methanogenic pathways. These models provide reasonable estimate of methanogenesis rates but cannot predict community structure. In this work, a trait-based model for methanogenic communities in peatlands is developed. The model divides methanogens commonly found in wetlands into ten guilds, with divisions based on factors such as substrate affinity, pH tolerance, and phylogeny. The model uses steady-state, mixotrophic Monod kinetics to model growth and assumes peatlands operate as a semi-batch system. An extensive literature review was performed to parameterize the model. The acetoclastic module of the model was validated against experimental data. It was found that this portion of the model was able to reproduce the major result of an experiment that examined competition between Methanosaeta and Methanosarcina species under irregular feeding conditions. The model was analyzed as a whole using Monte Carlo simulation methods. It was found that equilibrium membership is negatively correlated with a guild's half-substrate constant, but independent of the guild's yield. These results match what is seen in simple pairwise competition models. In contrast, it was found that both the half-substrate constant and yield affected a guild's numerical dominance. Lower half-substrate constants and higher yields led to a guild accounting for a greater fraction of community biomass. This is not seen in simple pairwise competitions models where only yield affects final biomass. As a whole, the development of this model framework and the accompanying analyses have laid the groundwork for a new class of more detailed methanogen community models that go beyond the two compartment acetoclastic-hydrogenotrophic assumption. .
ContributorsLopez Jr, Jaime Gerardo (Author) / Cadillo-Quiroz, Hinsby (Thesis director) / Marcus, Andrew (Committee member) / Chemical Engineering Program (Contributor) / Barrett, The Honors College (Contributor)
Created2017-05
Description
While biodiesel production from photosynthesizing algae is a promising form of alternative energy, the process is water and nutrient intensive. I designed a mathematical model for a photobioreactor system that filters the reactor effluent and returns the permeate to the system so that unutilized nutrients are not wasted, addressing these problems. The model tracks soluble and biomass components that govern the rates of the processes within the photobioreactor (PBR). It considers light attenuation and inhibition, nutrient limitation, preference for ammonia consumption over nitrate, production of soluble microbial products (SMP) and extracellular polymeric substance (EPS), and competition with heterotrophic bacteria that predominately consume SMP. I model a continuous photobioreactor + microfiltration system under nine unique operation conditions - three dilution rates and three recycling rates. I also evaluate the health of a PBR under different dilution rates for two values of qpred. I evaluate the success of each run by calculating values such as biomass productivity and specific biomass yield. The model shows that for low dilution rates (D = <0.2 d-1) and high recycling rates (>66%), nutrient limitation can lead to a PBR crash. In balancing biomass productivity with water conservation, the most favorable runs were those in which the dilution rate and the recycling rate were highest. In a second part of my thesis, I developed a model that describes the interactions of phototrophs and their predators. The model also shows that dilution rates corresponding to realistic PBR operation can washout predators from the system, but the simulation outputs depend heavily on the accuracy of parameters that are not well defined.
ContributorsWik, Benjamin Philip (Author) / Marcus, Andrew (Thesis director) / Rittmann, Bruce (Committee member) / School of Sustainability (Contributor) / Chemical Engineering Program (Contributor) / Barrett, The Honors College (Contributor)
Created2018-05
Description
Computer simulations are gaining recognition as educational tools, but in general there is still a line dividing a simulation from a game. Yet as many recent and successful video games heavily involve simulations (SimCity comes to mind), there is not only the growing question of whether games can be used for educational purposes, but also of how a game might qualify as educational. Endemic: The Agent is a project that tries to bridge the gap between educational simulations and educational games. This paper outlines the creation of the project and the characteristics that make it an educational tool, a simulation, and a game.
ContributorsFish, Derek Austin (Author) / Karr, Timothy (Thesis director) / Marcus, Andrew (Committee member) / Jones, Donald (Committee member) / Barrett, The Honors College (Contributor) / School of Mathematical and Statistical Sciences (Contributor) / Department of Physics (Contributor)
Created2013-05
Description
The human gut microbiome is a complex community of microorganisms. These microbes play an important role in host health by contributing essential compounds and acting as a barrier against pathogens. However, these communities and associated functions can be impacted by factors like disease and diet. In particular, microbial fermentation of dietary components like polysaccharides, proteins, and fats that reach the gut are being examined to better understand how these biopolymers are utilized and affect community structure. Thus, evaluating the accuracy of methods used to quantify specific macromolecules is crucial to gaining a precise understanding of how gut microbes hydrolyze those substrates. This study presents findings on the accuracy of the Megazyme RS kit (Rapid) modified for high performance liquid chromatography (HPLC) readings and the DC Protein Assay when performed on samples from complex gut media with potato starch treatments and bovine serum albumin (BSA) treatments. Overall, our data indicates that the megazyme RS kit needs further modification to detect expected starch content with the HPLC and that the DC Protein Assay is not suitable for specific protein analysis.
ContributorsKlein, Rachel Marie (Author) / Krajmalnik-Brown, Rosa (Thesis director) / Marcus, Andrew (Committee member) / School of Life Sciences (Contributor) / School of International Letters and Cultures (Contributor) / Barrett, The Honors College (Contributor)
Created2021-05
Description
Northern peatland carbon cycling is under close observation and is critical to include in models projecting the future effects of climate change as these ecosystems represent a significant source of atmospheric methane (CH4). Changes in the in situ conditions, brought upon by the warming climate, could alter the rates of organic matter decomposition and accelerate the emissions of greenhouse, changing northern peatland’s status as a carbon sink. In order to develop a better understanding of the climate’s effect on the microbial community composition, carbon decomposition cascade, and flux of CH4 and CO2, anoxic soil microcosms were supplemented with either glucose or propionate to test the distinct intermediary metabolism of four northern peatland sites with statistically similar geochemistry that exist across a climate gradient. Lutose (LT) and Bog Lake (BL) consumed the supplemented glucose at the highest rates, 42.6 mg/L per day and 39.5 mg/L per day respectively. Chicago Bog (CB) and Daring Lake (DL) consumed the supplemented propionate at the highest rates, 5.26 mg/L per day and 4.34 mg/L per day respectively. BL microcosms showed low levels of methanogenesis as CH4 concentrations reached a maximum of 2.61 µmol/g dry soil in the treatments. In DL, the site with the highest production of CH4, the low abundance of hydrogenotrophic methanogens (Methanocellaceae and Methanoregulaceae) and relatively steady concentrations of acetate and formate could indicate that these are the more desired methanogenic substrates. These findings are indicative of the differences in metabolic potential found across these geochemically similar peatlands, lending to climate variables being a major driver in microbial community potential. To further characterize the intermediary metabolism and the effect of the climate gradient in these sites, future experimentations should incorporate 13C DNA-stable isotope probing data, establish a mass balance of the system, and incubate the microcosms at their respective in situ temperatures.
ContributorsBourquin, Brandon Phillip (Author) / Cadillo-Quiroz, Hinsby (Thesis director) / Marcus, Andrew (Committee member) / Sarno, Analissa F. (Committee member) / School of Life Sciences (Contributor) / Barrett, The Honors College (Contributor)
Created2020-05