Browsing by Author "Aston, John E."

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Effects of cell condition, pH, and temperature on lead, zinc, and copper sorption to Acidithiobacillus caldus strain BC13
(2010-12) Aston, John E.; Apel, William A.; Lee, Brady D.; Peyton, Brent M.
This study describes the effects of cell condition, pH, and temperature on lead, zinc, and copper sorption to Acidithiobacillus caldus strain BC13 with a Langmuir model. Copper exhibited the highest loading capacity, 4.76Â±0.28mmolgâˆ’1, to viable cells at pH 5.5. The highest kL(binding-site affinity) observed was 61.2Â±3.0 Lmmolâˆ’1 to dehydrated cells at pH 4.0. The pHs that maximized loading capacities and binding-site affinities were generally between 4.0 and 5.5, where the sum of free-proton and complexedmetal concentrations was near a minimum. Of additional importance, lead, zinc, and copper sorbed to viable cells at pH values as low as 1.5. Previous studies with other acidithiobacilli did not measure viablecell sorption below pH 4.0. In separate experiments, desorption studies showed that far less copper was recovered from viable cells than any other metal or cell condition, suggesting that uptake may play an important role in copper sorption by At. caldus strain BC13. To reflect an applied system, the sorption of metal mixtures was also studied. In these experiments, lead, zinc, and copper sorption from a tertiary mixture were 40.2Â±4.3%, 28.7Â±3.8%, and 91.3Â±3.0%, respectively, of that sorbed in single-metal systems.
Effects of ferrous sulfate, inoculum history, and anionic form on lead, zinc, and copper toxicity to Acidithiobacillus caldus strain BC13
(2010-10) Aston, John E.; Peyton, Brent M.; Lee, Brady D.; Apel, William A.
The current study reports the single and combined toxicities of Pb, Zn, and Cu to Acidithiobacillus caldus strain BC13. The observed half-maximal inhibitory concentrations (IC50),Â±95% confidence intervals, for Pb, Zn, and Cu were 0.9Â±0.1 mM, 39Â±0.5 mM, and 120Â±8 mM, respectively. The observed minimum inhibitory concentrations (MIC) for Pb, Zn, and Cu were 7.5 mM, 75 mM, and 250 mM, respectively. When metals were presented in binary mixtures, the toxicities were less than additive. For example, when 50% of the Pb MIC and 50% of the Cu MIC were presented together, the specific growth rate was inhibited by only 59Â±3%, rather than 100%. In addition, the presence of ferrous iron in the growth media decreased Pb and Zn toxicity to A. caldus strain BC13.The importance of inoculum history was evaluated by pre-adapting cultures through subsequent transfers in the presence of Pb, Zn, and Cu at their respective IC50s. After pre-adaptation, cultures had specific growth rates 39Â±11, 32Â±7, and 28Â±12% higher in the presence of Pb, Zn, and Cu IC50s, respectively, compared with cultures that had not been pre-adapted. In addition, when cells exposed to the MICs of Pb, Zn, and Cu were harvested, washed, and re-inoculated into fresh, metal-free medium, they grew, showing that the cells remained viable with little residual toxicity. Finally, metal chlorides showed more toxicity than metal sulfates, and studies using sodium chloride or a mixture of metal sulfates and sodium chloride suggested that this was attributable to an additive combination of the metal and chloride toxicities.
Growth effects and assimilation of organic acids in chemostat and batch cultures of Acidithiobacillus caldus
(2011-01) Aston, John E.; Apel, William A.; Lee, Brady D.; Peyton, Brent M.
The ability of Acidithiobacillus caldus to grow aerobically using pyruvate, acetate, citrate, 2-ketoglutarate, succinate, and malate as either an electron donor and carbon source (heterotrophic growth), or as a carbon source when potassium tetrathionate was added as an electron donor (mixotrophic growth), was tested in chemostat cultures. Under both heterotrophic and mixotrophic conditions, organic acids were added to a sub-lethal concentration (50 μM). Under mixotrophic conditions, potassium tetrathionate was added to an excess concentration (10 mM). No cell growth was observed under heterotrophic conditions; however, effluent cell concentrations increased over threefold when pyruvate was coupled with potassium tetrathionate. Under these conditions, the effluent pyruvate concentration was reduced to below the detection limit (2 μM), and oxygen consumption increased by approximately 100%. Although pyruvate provided a carbon source in these experiments, ambient carbon dioxide was also available to the cells. To test whether At. caldus could grow mixotrophically using pyruvate as a sole carbon source and potassium tetrathionate as an electron donor, cells were batch cultured in a medium free of dissolved inorganic carbon, and with no carbon dioxide in the headspace. These experiments showed that At. caldus was able to convert between 65 ± 8 and 82 ± 15% of the pyruvate carbon to cellular biomass, depending on the initial pyruvate concentrations. This work is the first to identify a defined organic-carbon source, other than glucose, that At. caldus can assimilate. This has important implications, as mixotrophic and heterotrophic activity has been shown to increase mineral leaching in acidic systems.
In silico approaches to study mass and energy flows in microbial consortia: A syntrophic case study
(2009) Taffs, Reed L.; Aston, John E.; Brileya, Kristen A.; Jay, Zackary J.; Klatt, Christian G.; McGlynn, Shawn E.; Inskeep, William P.; Ward, David M.; Carlson, Ross P.
Background: Three methods were developed for the application of stoichiometry-based network analysis approaches including elementary mode analysis to the study of mass and energy flows in microbial communities. Each has distinct advantages and disadvantages suitable for analyzing systems with different degrees of complexity and a priori knowledge. These approaches were tested and compared using data from the thermophilic, phototrophic mat communities from Octopus and Mushroom Springs in Yellowstone National Park (USA). The models were based on three distinct microbial guilds: oxygenic phototrophs, filamentous anoxygenic phototrophs, and sulfate-reducing bacteria. Two phases, day and night, were modeled to account for differences in the sources of mass and energy and the routes available for their exchange.ResultsThe in silico models were used to explore fundamental questions in ecology including the prediction of and explanation for measured relative abundances of primary producers in the mat, theoretical tradeoffs between overall productivity and the generation of toxic by-products, and the relative robustness of various guild interactions.Conclusion: The three modeling approaches represent a flexible toolbox for creating cellular metabolic networks to study microbial communities on scales ranging from cells to ecosystems. A comparison of the three methods highlights considerations for selecting the one most appropriate for a given microbial system. For instance, communities represented only by metagenomic data can be modeled using the pooled method which analyzes a community's total metabolic potential without attempting to partition enzymes to different organisms. Systems with extensive a priori information on microbial guilds can be represented using the compartmentalized technique, employing distinct control volumes to separate guild-appropriate enzymes and metabolites. If the complexity of a compartmentalized network creates an unacceptable computational burden, the nested analysis approach permits greater scalability at the cost of more user intervention through multiple rounds of pathway analysis. The electronic version of this article is the complete one and can be found online at: http://www.biomedcentral.com/1752-0509/3/114
Near-Infrared Spectroscopy can Predict Anatomical Abundance in Corn Stover
(Frontiers Media SA, 2022-02) Cousins, Dylan S.; Otto, William G.; Rony, Asif Hasan; Pedersen, Kristian P.; Aston, John E.; Hodge, David B.
Feedstock heterogeneity is a key challenge impacting the deconstruction and conversion of herbaceous lignocellulosic biomass to biobased fuels, chemicals, and materials. Upstream processing to homogenize biomass feedstock streams into their anatomical components via air classification allows for a more tailored approach to subsequent mechanical and chemical processing. Here, we show that differing corn stover anatomical tissues respond differently to pretreatment and enzymatic hydrolysis and therefore, a one-size-fits-all approach to chemical processing biomass is inappropriate. To inform on-line downstream processing, a robust and high-throughput analytical technique is needed to quantitatively characterize the separated biomass. Predictive correlation of near-infrared spectra to biomass chemical composition is such a technique. Here, we demonstrate the capability of models developed using an “off-the-shelf,” industrially relevant spectrometer with limited spectral range to make strong predictions of both cell wall chemical composition and the relative abundance of anatomical components of the corn stover, the latter for the first time ever. Gaussian process regression (GPR) yields stronger correlations (average R2v = 88% for chemical composition and 95% for anatomical relative abundance) than the more commonly used partial least squares (PLS) regression (average R2v = 84% for chemical composition and 92% for anatomical relative abundance). In nearly all cases, both GPR and PLS outperform models generated using neural networks. These results highlight the potential for coupling NIRS with predictive models based on GPR due to the potential to yield more robust correlations.
Particle classification by image analysis improves understanding of corn stover degradation mechanisms during deconstruction
(Elsevier BV, 2023-03) Cousins, Dylan S.; Pedersen, Kristian P.; Otto, William G.; Rony, Asif Hasan; Lacey, Jeffrey A.; Aston, John E.; Hodge, David B.
iomass feedstock heterogeneity is a principal roadblock to implementation of the biorefinery concept. Even within an identical cultivar of corn stover, different bales contain not only varying abundance moisture, ash, glucan, and other chemical compounds, but also varying abundance of tissue anatomies (e.g., leaf, husk, cob, or stalk). These different anatomical components not only differ in their response to pretreatment and enzymatic hydrolysis to glucose, but also vary in their mechanical and conveyance properties. Although this heterogeneous nature of corn stover feedstock has been identified as a challenge, a fundamental knowledge gap of how these tissues behave during biorefining processing remains. In this work, we demonstrate the use of a commercial fiber image analyzer typically used for wood fiber characterization to monitor the particle size and shapes of non-woody feedstock during milling, pretreatment, and hydrolysis. Additionally, we present novel use of Gaussian process classification to distinguish bundle, parenchyma, and fiber particles to an accuracy of 96.4%. Quantitative probability distribution plots for characteristics such as length and roundness allow elucidation of particle morphology as pretreatment and enzymatic hydrolysis progress. In both stalk pith and stalk rind, particles peel into individual cells whose walls are subsequently fragmented during enzymatic hydrolysis.