College of Agriculture & Natural Resources
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The collections in this community comprise faculty research works, as well as graduate theses and dissertations.
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Item Evaluation of Hydrogen Sulfide Scrubbing Systems for Anaerobic Digesters on Two U.S. Dairy Farms(MDPI, 2019-12-04) Choudhury, Abhinav; Shelford, Timothy; Felton, Gary; Gooch, Curt; Lansing, StephanieHydrogen sulfide (H2S) is a corrosive trace gas present in biogas produced from anaerobic digestion systems that should be removed to reduce engine-generator set maintenance costs. This study was conducted to provide a more complete understanding of two H2S scrubbers in terms of efficiency, operational and maintenance parameters, capital and operational costs, and the effect of scrubber management on sustained H2S reduction potential. For this work, biogas H2S, CO2, O2, and CH4 concentrations were quantified for two existing H2S scrubbing systems (iron-oxide scrubber, and biological oxidation using air injection) located on two rural dairy farms. In the micro-aerated digester, the variability in biogas H2S concentration (average: 1938 ± 65 ppm) correlated with the O2 concentration (average: 0.030 ± 0.004%). For the iron-oxide scrubber, there was no significant difference in the H2S concentrations in the pre-scrubbed (450 ± 42 ppm) and post-scrubbed (430 ± 41 ppm) biogas due to the use of scrap iron and steel wool instead of proprietary iron oxide-based adsorbents often used for biogas desulfurization. Even though the capital and operating costs for the two scrubbing systems were low (<$1500/year), the lack of dedicated operators led to inefficient performance for the two scrubbing systems.Item FUNCTIONAL CHARACTERIZATION OF HEME TRANSPORTERS IN ZEBRAFISH(2017) Zhang, Jianbing; Hamza, Iqbal; Animal Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Hrg1 and Mrp5 are identified as eukaryotic heme importer and exporter, respectively. Two Hrg1 paralogs have been annotated in zebrafish genome, Hrg1a (Slc48a1b) and Hrg1b (Slc48a1a) with 84% homology in protein sequences. Hrg1a and hrg1b are widely expressed in embryonic and adult zebrafish. Yeast growth assays reveal that zebrafish Hrg1a and Hrg1b are both capable of heme import. However, hrg1a and hrg1b double knockout (hrg1 DKO) zebrafish generated by CRISPR/Cas9 has no overt defects in differentiation and maturation of erythroid cells. Knockdown of hrg1a in hrg1b mutants or vice versa does not impair erythroid lineage in zebrafish embryos. These genetic results suggest that Hrg1 is not required for maturation and hemoglobinization of primitive erythroid cells. Hrg1a and hrg1b mRNA are upregulated in adult kidneys and spleens upon PHZ-induced hemolysis, together with hmox1, a downstream heme degrading enzyme, suggesting that Hrg1 is involved in adult heme-iron recycling during erythrophagcytosis in kidney and spleen of adult zebrafish. DAB-enhanced Perl’s iron staining reveals that iron is accumulated in macrophages in the kidney and spleen in adult wild-type zebrafish. However, macrophages with positive Perl’s staining are rarely found in the kidney of hrg1 DKO and instead large amount of iron is deposited in renal tubules, suggesting defects in heme-iron recycling by kidney macrophages in hrg1 DKO under PHZ-induced hemolysis. Whole transcriptome sequencing of mRNA extracted from spleens and kidneys reveals massive differentially expressed genes in hrg1 DKO involved in immune response, lipid transport, oxidation-reduction process and proteolysis. These indicate that hrg1 DKO are deficient in recycling heme-iron derived from damaged RBCs in the absence of functional Hrg1. Phylogenetic analysis reveals that Mrp5 and Mrp9 are closed homologs in the zebrafish genome. Yeast growth assays reveal that both zebrafish Mrp5 and Mrp9 are capable of heme export. Morpholino knockdown of mrp5 and mrp9 in zebrafish showed severe anemia in developing embryos indicating their involvements in erythropoietic development. Subsequent generation and characterization of mrp5 and mrp9 mutants by CRISPR/Cas9 will further define the function of Mrp5 and Mrp9 during zebrafish development.Item FUNCTIONAL INSIGHTS INTO HRG-1-MEDIATED HEME TRANSPORT(2012) Yuan, Xiaojing; Hamza, Iqbal; Animal Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Heme is an essential cofactor involved in various biological processes including oxygen transport, xenobiotic detoxification, oxidative metabolism, gas sensing, circadian rhythm, signal transduction, microRNA processing and thyroid hormone synthesis. Heme is also an essential nutrient for parasites and is the major dietary iron source for humans. Despite our extensive understanding of the mechanisms of heme synthesis and degradation in eukaryotes, little is known as to how heme is transported and trafficked in eukaryotes. Recently, CeHRG-1 and CeHRG-4 were identified as the first bona fide heme importers/transporters using the heme auxotroph, Caenorhabditis elegans. To gain mechanistic insights into the heme transport function of HRG-1-related proteins, we conducted a structure-function analysis of CeHRG-1 and CeHRG-4 by exploiting yeast mutants that are genetically defective in heme synthesis. Our studies reveal that HRG-1-related proteins transport heme across membranes through the coordinated actions of strategically placed amino acids that are topologically conserved in both, the worm and human proteins. To further dissect the functional elements that dictate their intracellular localization, we generated a series of chimeras by swapping the amino and carboxy terminal segments of CeHRG-1 and CeHRG-4. Our analysis in yeast and mammalian cells demonstrate that the C-terminal domains are essential for membrane localization of the protein, while the N-terminal domains are important for proper function, and plausibly multimerization of HRG-1-related proteins. Currently, there are no pharmacological means to aid in the study of the cellular and physiological roles of eukaryotic heme transporters. We, for the first time, developed and executed a high-throughput screen of 233,360 compounds, to identify potential antagonists of HRG-1-related proteins by utilizing parasite heme transporters as the primary screening bait. Subsequent study in parasites will provide novel drug candidates against helminths that infect humans, livestock, and plants, as well as against genetic disorders of heme and iron metabolism in humans. Taken together, results from our studies will significantly advance novel functional and therapeutic insights into HRG-1 mediated heme transport in health and disease.