No description available.

No description available.

Succinic Acid (SA) was continuously produced using glucose and a Mg2CO3(OH)2 slurry as feed. Glucose feed concentrations of 20 and 40 g ℓ-1 were employed with corresponding Mg2CO3(OH)2 slurry concentrations of 60 and 120 g ℓ-1. The reactor pH was passively maintained between 6,4 and 6,8 by the buffer properties of the slurry in conjunction with the pH adjusted glucose feed. The suspended cell (SC) reactor was operated at 37°C with dilution rates varying between 0,04 h-1and 0,6 h-1. Groperl® particles were used as inert supports in the biofilm reactor; dilution rates of 0,11 h-1 to 1 h-1 were investigated. Two SC fermentations were conducted for the 20 g ℓ-1 glucose feed concentration and one for the 40 g ℓ-1. All SC fermentation runs were operated in excess of 12 days, while the biofilm run lasted 6,5 days. Fermentations were terminated only after contamination by lactic acid bacteria was observed. SC fermentations with the glucose feed concentration of 20 g ℓ-1 achieved a maximum SA productivity of 5,2 g ℓ-1h-1 at 0,6 h-1 with a corresponding SA yield of 0,65 g g-1. SC fermentations with the glucose feed concentration of 40 g ℓ-1 achieved a maximum SA productivity of 3,76 g ℓ-1h-1 at 0,4 h-1 with a SA yield of 0,82 g g-1. The results were comparable to the other continuous studies with Actinobacillus succinogenes, despite the fact that either biofilms or membranes were employed in these studies. The preliminary biofilm study demonstrated the capability of A. succinogenes to produce SA in high productivities and yields. SA productivities and yields for the dilution rates of 0,33 h-1 and 1,0 h-1, were 5,72 g ℓ-1h-1 (0,95 g g-1) and 12 g ℓ-1h-1 (1,0 g g-1), respectively. The biofilm reactor at 0,33 h-1 achieved twice the SA productivity of the SC reactor at 0,3 h-1 with a 42 % increase in SA yield. Copyright / Dissertation (MEng)--University of Pretoria, 2012. / Chemical Engineering / unrestricted

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A buffered growth medium was developed that sustained a significantly greater concentration of various strains of Streptococcus lactis and Streptococcus cremoris than did milk. The active buffering ingredients of this medium were magnesium hydroxide, ammonium and sodium salts of phosphate and citrate. This medium was entitled Lactic Culture Buffered Growth medium (LABGRO) and possessed about 8 times the buffering strength between pH 6.6 and 5.1. Significant differences in growth and acid production rates were noted among Prt+ and Prt- lactic strains evaluated. Also noted were significant differences in cellular acid production rates. The two Prt- strains having the slowest growth rate in milk were selected as test strains to evaluate stimulants. Three strains of Kluyveromyces fragilis were aerobically propagated in whey medium and afterwards subjected to autolysis conditions. Whey protein and casein were added to some yeast samples prior to initiation of autolysis. To some of these latter samples, pepsin was added. After autolysis the yeast and yeast-protein samples were dried and their stimulatory properties for lactic culture propagation were evaluated with a test strain and LABGRO medium. No product was found to be as stimulatory as a control commercial yeast autolysate. Yeast-protein samples with added pepsin were markedly more stimulatory than the other samples. The whey-derived yeast extract significantly improved the lactic culture growth stimulating properties of protein hydrolysates.

Tree peony is known worldwide for its excellent ornamental and medical values, but recent reports that their seeds contain over 40% α-linolenic acid (ALA), an essential fatty acid for humans drew additional interest of biochemists. To understand the key factors that contribute to this rich accumulation of ALA, we carried out a comprehensive study of oil accumulation in developing seeds of nine wild tree peony species. The fatty acid content and composition was highly variable among the nine species; however, we selected a high- (P. rockii) and low-oil (P. lutea) accumulating species for a comparative transcriptome analysis. Similar to other oilseed transcriptomic studies, upregulation of select genes involved in plastidial fatty acid synthesis, and acyl editing, desaturation and triacylglycerol assembly in the endoplasmic reticulum was noted in seeds of P. rockii relative to P. lutea. Also, in association with the ALA content, transcript levels for fatty acid desaturases (SAD, FAD2 and FAD3), which encode for enzymes necessary for polyunsaturated fatty acid synthesis were higher in P. rockii compared to P. lutea. We further showed that the overexpression of PrFAD2 and PrFAD3 in Arabidopsis increased linoleic and α-linolenic acid content, respectively and modulated their final ratio in the seed oil. In conclusion, we identified the key steps that contribute to efficient ALA synthesis and validated the necessary desaturases in P. rockii that are responsible for not only increasing oil content but also modulating 18:2/18:3 ratio in seeds. Together, these results will aid to improve essential fatty acid content in seeds of tree peonies and other crops of agronomic interest.

The increasing need for healthy edible oil has driven us to identify α-linolenic acid (ALA)-rich species and identify key biochemical steps in ALA synthesis. Seeds of tree peony species are rich in unsaturated fatty acid content with > 40% ALA in the total fatty acid. However, fatty acid content and composition is variable among the tree peony germplasm. To this extent, a comparative study was carried out to identify the key genes responsible for differential oil accumulation among nine wild tree peony species. Subsequent to analyzing fatty acid content and composition of the seeds from nine tree peony species, a high- (P. rockii) and low-oil (P. lutea) accumulating species were selected for transcriptome analysis. Gene expression analysis revealed upregulation of select genes involved in plastidial fatty acid synthesis, and acyl editing, desaturation and triacylglycerol assembly in the endoplasmic reticulum in seeds of P. rockii relative to P. lutea. Also, in association with ALA content in seeds, transcript levels for fatty acid desaturases (SAD, FAD2 and FAD3), which encode for enzymes necessary for polyunsaturated fatty acid synthesis were higher in P. rockii compared to P. lutea. Additionally, we showed that the overexpression of PrFAD2 and PrFAD3 in Arabidopsis increased linoleic and α-linolenic acid content, respectively and modulated their final ratio in the seed oil. In conclusion, we identified the key steps that contribute to efficient ALA synthesis and validated the necessary desaturases in P. rockii that are responsible for not only increasing oil content but also modulating 18:2/18:3 ratio in seeds. Together, these results will aid to improve essential fatty acid content in seeds of tree peonies and other crops of agronomic interest.

Inferential control of boric acid production system using the reaction of colemanite with sulfuric acid in four continuously stirred tank reactors (CSTR) connected in series is aimed. In this control scheme, pH of the product is measured on-line instead of boric acid concentration for control purposes. An empirical correlation between pH and boric acid concentration is developed using the collected data in a batch reacting system in laboratory-scale and this correlation is utilized in the control system for estimator design. The transfer function model of the 4-CSTR system previously obtained is used in the MPC controller design. In the experiments done previously for the modelling of 4-CSTR system, it was observed that the reaction goes complete within the first reactor. Therefore, the control is based on the measurements of pH of the second reactor by manipulating the flow rate of sulfuric acid given to the first reactor, while the flow rate of colemanite fed to the system is considered as disturbance. The designed controller&rsquo / s performance is tested for set point tracking, disturbance rejection and robustness issues using a simulation program. It is found that, the designed controller is performing satisfactorily, using the inferential control strategy for this complex reacting system.

In this study, the effects of bioprocess operation parameters on aromatic amino acid synthesis performance of Bacillus acidocaldarius were investigated. Firstly, in laboratory scale shake-bioreactors, a defined medium was designed in terms of its carbon and nitrogen sources, to achieve the highest cell concentration. Thereafter, the effects of bioprocess operation parameters, i.e., pH and temperature were investigated / and the optimum medium contained (kg m-3): fructose, 8 / (NH4)2HPO4, 5 / CaCl2, 0.2 / KH2PO4, 2 / NaH2PO4.2H2O, 7.318 / Na2HPO4, 0.0438 / Mg(CH3COO)2.4H2O, 87&times / 10-3 / 1 , MgSO4.7H2O / 2&times / 10-3, FeSO4.7H2O / 2&times / 10-3, ZnSO4.7H2O / 15 &times / 10-5, MnSO4.H2O / 2&times / 10-5, CuSO4.5H2O with pH0 =5, T=55&amp / #61616 / C, N=175 min-1. In this medium, the bacteria produced L-tryptophan at the highest concentration of 0.204 kg m-3 and L-phenylalanine at a maximum concentration of 0.0106 kg m-3 with no L-tyrosine production. Finally the fermentation and oxygen transfer characteristics of the bioprocess were investigated in 3.0 dm3 pilot scale bioreactors. The effects of oxygen transfer were investigated at four different conditions at the parameters air inlet rates of QO/VR =0.2, and 0.5 vvm, and agitation rates of N= 250, 500, 750 min-1. The effect of pH was investigated at pH=5 uncontrolled and controlled operations. The variations in cell, fructose, amino acid and organic acid concentrations with the cultivation time / and using the dynamic method, the oxygen uptake rate and the liquid phase mass transfer coefficient values throughout the growth phase of the bioprocess / the yield and maintenance coefficients were determined. The aromatic amino acids produced at the highest and the least amount and frequency were L-tryptophan and L-tyrosine, respectively. The highest L-tryptophan production, 0.32 kg m-3 in 17 hour was at 0.2 vvm and 500 min-1. Among all operations, the highest L-tryptophan was produced at the lowest oxygen transfer condition. Controlled-pH conditions produced more L-tryptophan.

abstract: On average, our society generates ~0.5 ton of municipal solid waste per person annually. Biomass waste can be gasified to generate synthesis gas (syngas), a gas mixture consisting predominantly of CO, CO2, and H2. Syngas, rich in carbon and electrons, can fuel the metabolism of carboxidotrophs, anaerobic microorganisms that metabolize CO (a toxic pollutant) and produce biofuels (H2, ethanol) and commodity chemicals (acetate and other fatty acids). Despite the attempts for commercialization of syngas fermentation by several companies, the metabolic processes involved in CO and syngas metabolism are not well understood. This dissertation aims to contribute to the understanding of CO and syngas fermentation by uncovering key microorganisms and understanding their metabolism. For this, microbiology and molecular biology techniques were combined with analytical chemistry analyses and deep sequencing techniques. First, environments where CO is commonly detected, including the seafloor, volcanic sand, and sewage sludge, were explored to identify potential carboxidotrophs. Since carboxidotrophs from sludge consumed CO 1000 faster than those in nature, mesophilic sludge was used as inoculum to enrich for CO- and syngas- metabolizing microbes. Two carboxidotrophs were isolated from this culture: an acetate/ethanol-producer 99% phylogenetically similar to Acetobacterium wieringae and a novel H2-producer, Pleomorphomonas carboxidotrophicus sp. nov. Comparison of CO and syngas fermentation by the CO-enriched culture and the isolates suggested mixed-culture syngas fermentation as a better alternative to ferment CO-rich gases. Advantages of mixed cultures included complete consumption of H2 and CO2 (along with CO), flexibility under different syngas compositions, functional redundancy (for acetate production) and high ethanol production after providing a continuous supply of electrons. Lastly, dilute ethanol solutions, typical of syngas fermentation processes, were upgraded to medium-chain fatty acids (MCFA), biofuel precursors, through the continuous addition of CO. In these bioreactors, methanogens were inhibited and Peptostreptococcaceae and Lachnospiraceae spp. most likely partnered with carboxidotrophs for MCFA production. These results reveal novel microorganisms capable of effectively consuming an atmospheric pollutant, shed light on the interplay between syngas components, microbial communities, and metabolites produced, and support mixed-culture syngas fermentation for the production of a wide variety of biofuels and commodity chemicals. / Dissertation/Thesis / Doctoral Dissertation Civil, Environmental and Sustainable Engineering 2017