Matching Items (194)
Description
Background
Syngas fermentation, the bioconversion of CO, CO[subscript 2], and H[subscript 2] to biofuels and chemicals, has undergone considerable optimization for industrial applications. Even more, full-scale plants for ethanol production from syngas fermentation by pure cultures are being built worldwide. The composition of syngas depends on the feedstock gasified and the gasification conditions. However, it remains unclear how different syngas mixtures affect the metabolism of carboxidotrophs, including the ethanol/acetate ratios. In addition, the potential application of mixed cultures in syngas fermentation and their advantages over pure cultures have not been deeply explored. In this work, the effects of CO[subscript 2] and H[subscript 2] on the CO metabolism by pure and mixed cultures were studied and compared. For this, a CO-enriched mixed culture and two isolated carboxidotrophs were grown with different combinations of syngas components (CO, CO:H[subscript 2], CO:CO[subscript 2], or CO:CO[subscript 2]:H[subscript 2]).
Results
The CO metabolism of the mixed culture was somehow affected by the addition of CO[subscript 2] and/or H[subscript 2], but the pure cultures were more sensitive to changes in gas composition than the mixed culture. CO[subscript 2] inhibited CO oxidation by the Pleomorphomonas-like isolate and decreased the ethanol/acetate ratio by the Acetobacterium-like isolate. H[subscript 2] did not inhibit ethanol or H[subscript 2] production by the Acetobacterium and Pleomorphomonas isolates, respectively, but decreased their CO consumption rates. As part of the mixed culture, these isolates, together with other microorganisms, consumed H[subscript 2] and CO[subscript 2] (along with CO) for all conditions tested and at similar CO consumption rates (2.6 ± 0.6 mmol CO L[superscript −1] day[superscript −1]), while maintaining overall function (acetate production). Providing a continuous supply of CO by membrane diffusion caused the mixed culture to switch from acetate to ethanol production, presumably due to the increased supply of electron donor. In parallel with this change in metabolic function, the structure of the microbial community became dominated by Geosporobacter phylotypes, instead of Acetobacterium and Pleomorphomonas phylotypes.
Conclusions
These results provide evidence for the potential of mixed-culture syngas fermentation, since the CO-enriched mixed culture showed high functional redundancy, was resilient to changes in syngas composition, and was capable of producing acetate or ethanol as main products of CO metabolism.
Syngas fermentation, the bioconversion of CO, CO[subscript 2], and H[subscript 2] to biofuels and chemicals, has undergone considerable optimization for industrial applications. Even more, full-scale plants for ethanol production from syngas fermentation by pure cultures are being built worldwide. The composition of syngas depends on the feedstock gasified and the gasification conditions. However, it remains unclear how different syngas mixtures affect the metabolism of carboxidotrophs, including the ethanol/acetate ratios. In addition, the potential application of mixed cultures in syngas fermentation and their advantages over pure cultures have not been deeply explored. In this work, the effects of CO[subscript 2] and H[subscript 2] on the CO metabolism by pure and mixed cultures were studied and compared. For this, a CO-enriched mixed culture and two isolated carboxidotrophs were grown with different combinations of syngas components (CO, CO:H[subscript 2], CO:CO[subscript 2], or CO:CO[subscript 2]:H[subscript 2]).
Results
The CO metabolism of the mixed culture was somehow affected by the addition of CO[subscript 2] and/or H[subscript 2], but the pure cultures were more sensitive to changes in gas composition than the mixed culture. CO[subscript 2] inhibited CO oxidation by the Pleomorphomonas-like isolate and decreased the ethanol/acetate ratio by the Acetobacterium-like isolate. H[subscript 2] did not inhibit ethanol or H[subscript 2] production by the Acetobacterium and Pleomorphomonas isolates, respectively, but decreased their CO consumption rates. As part of the mixed culture, these isolates, together with other microorganisms, consumed H[subscript 2] and CO[subscript 2] (along with CO) for all conditions tested and at similar CO consumption rates (2.6 ± 0.6 mmol CO L[superscript −1] day[superscript −1]), while maintaining overall function (acetate production). Providing a continuous supply of CO by membrane diffusion caused the mixed culture to switch from acetate to ethanol production, presumably due to the increased supply of electron donor. In parallel with this change in metabolic function, the structure of the microbial community became dominated by Geosporobacter phylotypes, instead of Acetobacterium and Pleomorphomonas phylotypes.
Conclusions
These results provide evidence for the potential of mixed-culture syngas fermentation, since the CO-enriched mixed culture showed high functional redundancy, was resilient to changes in syngas composition, and was capable of producing acetate or ethanol as main products of CO metabolism.
ContributorsEsquivel Elizondo, Sofia (Author) / Delgado, Anca (Author) / Rittmann, Bruce (Author) / Krajmalnik-Brown, Rosa (Author) / Biodesign Institute (Contributor) / Swette Center for Environmental Biotechnology (Contributor) / Ira A. Fulton School of Engineering (Contributor) / School of Sustainable Engineering and the Built Environment (Contributor)
Created2017-09-16
Description
Bright electron beams with photo injectors are used for XFELS, UEM, UED, and accelerators for fundamental physics research. Essential to a photocathode’s use in a photoinjector system is the minimum MTE achievable for a beam generated with it. Atomically ordered, single-crystalline photocathodes are ideal, and multiple materials have been identified for their potential as photocathodes, but not properly tested. At the Arizona State University Photoemission and Bright Beams Laboratory, we have developed a 200 kV crycooled electron gun and vacuum beamline with widely available parts to test a variety of photocathode candidates for bright electron beams, as well as programs to process this data to obtain MTE and emittance measurements.
ContributorsMama, Jo (Author) / Karkare, Siddharth (Thesis director) / Owusu, Peter (Committee member) / Barrett, The Honors College (Contributor) / Department of Physics (Contributor) / School of Mathematical and Statistical Sciences (Contributor)
Created2025-05
Description
Rubisco activase is a chaperone-like AAA+ ATPase essential for maintaining
photosynthetic activity by releasing inhibitory sugar phosphates from Rubisco’s active site. In
higher plants, including spinach, Rca exists in α and β isoforms and is believed to function
primarily as a nucleotide-dependent hexamer. Despite recent structural insights, questions remain
about the full-length assembly of Rca and its interaction with Rubisco under physiological
conditions.
Here, we present a detailed biochemical and structural analysis of spinach β-Rca,
including an improved purification protocol, oligomerization behavior under defined nucleotide
conditions, and structural characterization using negative stain electron microscopy. Both
SoβRca and Rubisco were purified to homogeneity, with SoβRca consistently forming hexamers
in the presence of ATPγS. When mixed under activating conditions, SoβRca and Rubisco
produced a reproducible early-eluting peak in SEC, distinct from either protein alone. Negative
stain imaging of these fractions revealed large, asymmetric assemblies containing multiple
Rubisco-like particles–raising the possibility of higher-order interactions. However, no strong
conclusion can be drawn due to the low abundance of SoβRca in these fractions and the
uncertainty surrounding the identity and stoichiometry of the observed complexes.
Higher-resolution work, and further trials are required to resolve the structure and determine the
relevance of these complexes.
ContributorsCarsten, Alexander (Author) / Chiu, Po-Lin (Thesis director) / Klein-Seetharaman, Judith (Committee member) / Sarkar, Susanta (Committee member) / Barrett, The Honors College (Contributor) / School of Molecular Sciences (Contributor) / School of Mathematical and Statistical Sciences (Contributor) / Department of Physics (Contributor)
Created2025-05
Description
Cadmium Telluride (CdTe) is a promising II–VI photovoltaic material, offering a detailed-balance efficiency limit around 30%. However, achieving this potential in practice requires minimizing non-radiative losses. This thesis examines the effects of black-body radiation of a CdTe/InSb solar cell absorber layer. Here, both experimental and theoretical approaches are used to understand how black-body emission and recombination losses influence solar cell device performance. Key topics include black-body radiation fundamentals, calibration of a black-body source, optical absorption in monocrystalline vs. polycrystalline CdTe absorbers, the Shockley–Queisser limit under radiative recombination, and photoluminescence quantum efficiency (PLQE) measurements. The goal was to understand how intrinsic thermal radiation and device design limit open-circuit voltage and efficiency, and how advanced structural engineering such as heterostructure barrier layers can mitigate these limits. In fact, the PLQE of the measured sample appeared to be extremely low: 6×10^(-7)%, which indicated a very large non-radiative recombination. Transmission Electron Microscopy and Solar Cell Modelling were utilized to explain this result. By using modified Shockley–Queisser approach to account for large non-radiative recombination, a more realistic maximum efficiency of 9.28% was calculated.
ContributorsVoinkov, Ky (Author) / Zhang, Yong-Hang (Thesis director) / Smith, David (Committee member) / Ju, Zheng (Committee member) / Barrett, The Honors College (Contributor) / Materials Science and Engineering Program (Contributor) / Department of Physics (Contributor) / School of Mathematical and Statistical Sciences (Contributor)
Created2025-05