Dissertations / Theses on the topic 'Nitrogen-limited'

An Entrapped-Mixed-Microbial-Cell (EMMC) process was investigated for its simultaneous removal of carbon and nitrogen in a single bioreactor with the influent COD/N ratio varying from 4 to 15 and influent alkalinity of 140 mg CaCO3/L and 230 mg CaCO3/L. The reactor was operated with alternate schedules of intermittent aeration. Two different sizes of carriers (10 * 10 * 10 mm3 and 20 * 20 * 20 mm3) were studied. The medium carrier (10 * 10 * 10 mm3) system presents higher nitrogen removal and COD removal compared to the large carrier system. The nitrogen removal efficiency is related to the ratio of COD/N in the influent. With the increase of the COD/N ration in the influent, the nitrogen removal efficiency is increased. The average reductions of nitrogen were over 92% and the average reductions of SCOD and BOD5 are over 95% and 97%, respectively, in the medium carrier system. This is operated at the HRT of 12 hours and 0.5 hour aeration and 2 hours of non-aeration, and the COD/N ratio of 15 in the influent. Changing alkalinity from 140 to 230 mg CaCO3/L has no effect in both large and medium carriers for the nitrogen removal efficiency. The pH, oxidation – reduction potential (ORP) and dissolved oxygen (DO) were used to monitor the biological nitrogen removal. It was found that the ORP (range from -100 to 300 mV) can be used to provide better effluent quality measured as total-nitrogen of less than 10 mg/L. Also, the impact of influent COD/N ratio on the effluent quality (measured as Inorg.-nitrogen) for the EMMC process is very important. Compared to other two compact biological wastewater treatment processes, membrane bioreactor (MBR) and moving bed biofilm reactor (MBBR), the EMMC process with the intermittent aeration has higher removal efficiencies of carbon and nitrogen, easier operation, lower O&M cost, lower energy requirement, and more compact. The total cost requirement is less than $3.27 per 1000 gallons (3.785 m 3) of treated settled domestic sewage per day. It is apparent that the EMMC process is technically feasible for the simultaneous removal of carbon and nitrogen under the operation on a schedule of intermittent aeration and suitable to be used for replacement or upgrading of existing treatment plant at land limited area.

This experiment investigated causes of seasonality of δ15N and δ13C values in Thalassia testudinum leaf tissue by manipulating plant demand and nutrient supply in situ for 13 months. I clearly demonstrated that seagrass elemental content, stable C and N isotopic content, morphology and the concentration of NH4+ seagrass porewaters directly respond to manipulations of resources and also by the plant demand for nutrients to support growth. Isotopic values displayed marked seasonality with heavier values found in summer (δ15N=5.0% δ13C=-5.7%o) and lighter values in winter (δ15N=1.7%o δ13C= -9.4%o). Calculations of Δ (δ15N source DIN- δ15N plant product) indicate that T. testudinum is able to strongly fractionate against source pool DIN. Interpretation of an enriched N signature as pollution-derived must first recognize the isotopic seasonality of the plant demand relative to the nutrient supply. Only when these links have been explained can the full relevance of δ15N values be applied.

Mathematical models of a nitritation: anaerobic ammonia oxidation (anammox)-coupled biofilm in a counter-diffusion hollow fiber membrane bioreactor (HFMBR) and a nitritation: anammox-coupled biofilm in a co-diffusion rotating biological contactor (RBC) were developed and implemented using AQUASIM. Four different start-up scenarios on the nitritation: anammox-coupled biofilm in an HFMBR were investigated. The supply of oxygen was simulated with the flow through the lumen of the hollow fiber membrane. For the four scenarios, two scenarios investigated the start-up when nitrite was supplied in the feed while the other two scenarios investigated when the source of nitrite was through nitritation only. The results showed that the presence of nitrite in the feed facilitated the start-up of the reactor. In addition, the results also showed that increasing oxygen flux through the membrane up to a certain ratio of ammonia flux with oxygen flux affected reactor performance by improving nitrogen removal and reducing start up time. For the nitritation: anammox-coupled biofilm in an RBC, four different process options were investigated: the number of reactors, the initial anammox (AnAOB) biomass fraction, the bulk oxygen concentration and the maximum biofilm thickness. Modeling results revealed that the steady state total nitrogen removal in RBC reactors in series occurred primarily in the first and second reactors. It is concluded that the number of reactors in series dictates the effluent performance and, therefore, this number can be selected depending upon the desired total nitrogen removal. Simulation results also revealed that increasing the initial AnAOB biomass fraction from 0.01% to 1.0% had no effect in the steady state nitrogen removal but had an effect in the required time to reach the steady state total nitrogen removal and the maximum biofilm thickness. Modeling results of the third process option showed that increasing the bulk oxygen concentration in the reactor from 0.2 g/m3 to 5 g/m3 linearly increased the steady state total nitrogen removal and reduced the time to reach the maximum biofilm thickness. Beyond 5 g/m3, steady state total nitrogen removal decreased. In addition, simulation results revealed that the thicker biofilm clearly showed a more linear correlation between the increase in bulk oxygen concentration and the increase in the steady state total nitrogen removal within a range of bulk oxygen concentrations. The results showed that RBC performance could be controlled by several process options: the number of reactors in series, initial biomass fraction, the bulk oxygen concentration and the maximum biofilm thickness. The mathematical modeling results for the HFMBR and RBC have shown that both have potential as carriers for nitritation: anammox-coupled biofilms targeted at the removal of nitrogen in the wastewater.
Master of Science

In an effort to develop cost-effective technologies for the removal of ammonium nitrogen from dairy waste, a novel biological wastewater treatment process, utilizing anaerobic ammonium oxidation (anammox), referred to as Oxygen-Limited Autotrophic Nitrification and Denitrification (OLAND) was examined. Due to the potential use of OLAND-based systems in dairy manure management, a detailed water quality assessment of a modern dairy farm manure treatment-system was conducted. The Johnson Highland Dairy Farm, Glade Spring, Virginia, was selected for this assessment and a comprehensive analysis of the wastewater characteristics throughout the confined animal feeding operation was completed. The results suggest that ammonia concentrations in the anaerobic storage facility was high enough to justify use of treatment technologies that reduce ammonia loads in stored dairy waste. A lightly loaded Fixed Film Bioreactor (FFBR), in which the OLAND process was desired to occur, was then constructed in the laboratory and monitored over 51 days. Of particular interest was the time taken to achieve stable performance of this OLAND system. Furthermore, a protocol was developed to determine whether OLAND based metabolism was occurring. Ammonium nitrogen removal efficiency in the FFBR throughout the 51-day monitoring period was high, averaging approximately 95 % for the length of the study. From day 32 to 51, simultaneous removal of both ammonium and nitrite with a low level of concomitant nitrate production was observed, a key indicator of possible anammox activity. Stoichiometric ratios calculated for the FFBR compared favorably with those already established for OLAND systems. The developed protocol, incorporating anaerobic and aerobic batch experiments, to verify the occurrence of OLAND based metabolism did not yield expected results and described poorly what was being observed in the FFBR. Volatilization of ammonia during the experimental test was suspected and should be controlled when the protocol is performed in the future.
Master of Science

Almost all life on earth is directly or indirectly dependent on phytoplankton primary productivity. In many aquatic systems, phytoplankton primary production is limited by the availability of nitrogen in the environment. Therefore, studying the dynamics of nitrogen uptake and assimilation by phytoplankton cells is critically important for understanding many ecosystem services and global biogeochemical cycles. Mathematical models are particularly powerful tools for analyzing dynamic processes in many areas of ecology, but so far their employment with phytoplankton time-series has been limited. Specifically, published phytoplankton models are unable to explicitly account for the role of different nitrogen forms on cell division and can only be calibrated with time-consuming and impractical monitoring of specific variables. Overall, this thesis aimed to expand previous models by incorporating important processes regulating nitrogen utilization in phytoplankton cells, and by improving their calibration with proxy data routinely monitored in experimental studies. Nitrate and ammonium are the two most important sources of inorganic nitrogen driving phytoplankton primary productivity. The performance of phytoplankton species changes when reared with either of these two forms of nitrogen individually, as well as when they are both present, or when cells have experienced previous periods of nitrogen starvation. However, current functional responses are unable to capture transient and interactive dynamics of nitrate and ammonium uptake, nor can they capture how these two forms of nitrogen differently influence cell division. Hence, in chapter 2, I designed and empirically tested a new process-based model that includes uptake of both nitrate and ammonium, as well as the effects of starvation length and inhibition of nitrate uptake by ammonium on phytoplankton cell division. Results for the green alga Chlorella sp. showed that a single parameterization of the model performed well across data from laboratory cultures started at 12 different initial conditions. This new model allowed for the first time the quantification of nitrate-ammonium utilization traits of a phytoplankton species. This contributes to a more comprehensive understanding of the factors underpinning the high variation in nitrate-ammonium assimilation observed in natural and engineered systems. Characterizing resource utilization traits of a species is particularly important for identifying processes promoting biodiversity and ecosystem functioning in nature. Most trait-based studies define species by their mean trait values and assume intraspecific trait variability to be negligible compared to interspecific differences. However, phenotypic plasticity may be an important source of variation in phytoplankton species, which are well known for their ability to rapidly adjust their cell size according to biotic and abiotic conditions. In chapter 3, I used the model designed in chapter 2 to evaluate the effects of cell size plasticity on the nitrogen utilization traits of the green alga Desmodesmus armatus, reared under different nitrogen sources (nitrate, ammonium, or both) and nitrogen histories (N-replete and N-deplete). Results showed that nitrate-ammonium utilization traits depended substantially on mean cell size and nitrogen history and that representing phytoplankton species by their mean trait values (as per traditional approaches) could underestimate the actual performance of a species by as much as one order of magnitude. These results highlight the ecological importance of intraspecific variability in determining the ability of a species to adjust to new environmental conditions. Biologically, it is well-known that the internal concentration of the most limiting nutrient (cell "quota") is what determines the growth rate of a cell. Given the critical importance of nitrogen for phytoplankton cell division, monitoring nitrogen quota is important to understand aquatic primary productivity, phytoplankton ecology, eutrophication and algal blooms. However, current methods to directly monitor nitrogen quota remain inaccurate, expensive, destructive, and time-consuming. Thus, in chapter 4, I tested the hypothesis that optical changes in single cells, which can be rapidly and accurately monitored with a standard flow cytometer, can provide reliable proxies for per-cell internal nitrogen. Results from four freshwater phytoplankton species showed that cellular nitrogen quota could be estimated accurately (R² = 0.9) from cell optical properties and medium nitrogen, and that the relationship did not change among different species or different initial conditions. In particular, red chlorophyll autofluorescence (from here on simply "red fluorescence") was the most important variable explaining 77% of the total variability in total cell nitrogen. These results indicate that optical flow cytometric variables are a reliable and non-destructive method to estimate nitrogen quota in phytoplankton cells. Finding an efficient proxy to evaluate cell nitrogen quota is particularly valuable for extending the applicability of phytoplankton models. The internal nitrogen status of a cell is critical to analyze the dynamics of nitrogen-limited phytoplankton populations, but accounting for this process in phytoplankton models requires monitoring per-cell nitrogen quota, which is time-consuming, inaccurate, and destructive. Instead, the method I proposed in chapter 4 to quantify nitrogen quota using the optical properties of individual cells is rapid, precise, accurate, and non-destructive. Hence, in chapter 5, I evaluated a new way to model phytoplankton populations, consisting in explicitly including cell optical properties as a proxy for nitrogen quota within phytoplankton Quota models. Results showed that accounting for cell optical properties could improve the performance of phytoplankton population models while still accounting for the biologically important process of cell nitrogen storage. More broadly, these findings highlight the importance of identifying proxy variables for the internal condition of an organism when using population models to analyze species dynamics. The overarching aim of my thesis was to improve current phytoplankton models for the analysis of phytoplankton nitrogen utilization. This was achieved by presenting and calibrating a new mathematical framework describing the dynamics of nitrate-ammonium utilization in phytoplankton populations (chapter 2), by evaluating the effect of mean cell size and previous nitrogen history in determining the nitrogen utilization of a cell (chapter 3), and by documenting the importance of cell optical properties for explaining the dynamics of phytoplankton populations (chapters 4 and 5). These findings improve our ability to identify, analyze, and understand the relationships between nitrogen concentrations in the environment and phytoplankton populations. More broadly, this thesis offers new mathematical tools to better investigate the processes regulating phytoplankton primary productivity in nature and engineered systems.

Nitrogen deficiency can often lead to slow or sluggish fermentation, resulting in wine out of specification and at risk of oxidation and microbial contamination. Problems due to nitrogen deficiency can be rectified by optimising grape chemistry (through vineyard fertilization), or more commonly supplementing the fermentation with ammonium salts. An alternative is to use wine yeast that can utilize nitrogen efficiently and complete fermentation more reliably. However, to develop ‘nitrogen efficient’ yeast, it is important to understand how such yeast can utilize nitrogen effectively by identifying genes that influence fermentation performance over a range of nitrogen concentrations. Past research related to the identification of genes influencing nitrogen efficiency under fermentative conditions is largely confined to laboratory yeast. Investigation of the ~5,000 non-essential genes in yeast is possible through research tools such as deletion libraries (collections of strains, each with a single gene deletion). Several genomewide studies have successfully used deletion libraries in the auxotrophic background of laboratory yeast to investigate phenotypes in response to exposure to single stress factors associated with fermentation. However, the need to supplement with amino acids to overcome auxotrophies makes quantitative physiological studies in nitrogen limiting conditions impractical. Therefore, in this study, we have used a prototrophic deletion collection in both laboratory and wine yeast backgrounds to identify genes influencing fermentation performance. Screening (micro-fermentation; 600 μL) of the prototrophic laboratory yeast deletion library (BY4741; 5,372 deletants) and the partial wine yeast library (AWRI1631; 1,844 deletants) for growth and consumption of sugar and nitrogen under limiting (75 mg FAN L⁻¹) and non-limiting nitrogen (450 mg FAN L⁻¹) conditions identified deletants with improved fermentation. To better understand the role of individual genes in fermentation, candidate gene sets from each screen were compared to each other and to other published data sets from genome wide transcriptomic analyses related to fermentation. Wine yeast deletants that enabled shortened micro-fermentation duration in low nitrogen conditions were further investigated, since the experiment best represented nitrogen deficient grape must associated with problematic fermentation. Fifteen deletants completed fermentation quicker than the wildtype (c.a. a 15-59% time reduction) when tested in larger (100 mL) fermentations. This group of genes were annotated to biological processes including protein modification, transport, metabolism and ubiquitination (UBC13, MMS2, UBP7, UBI4, BRO1, TPK2, EAR1, MRP17, MFA2 and MVB12), signalling (MFA2) and amino acid metabolism (AAT2). Among the genes identified, MFA2 (mating a-factor), which conferred a 34% decrease in fermentation duration, was further investigated. We were interested to understand how deletion of this mating type gene affected fermentation since a link between these metabolic pathways would be novel. The 15 strains identified in this study, which were fermentation proficient in a ‘wine-like', limited nitrogen condition, provide a basis to better understand how yeast adapt to nitrogen limitation during fermentation. Furthermore, the corresponding genes can be targeted in second generation strain improvement programs, using tools such as CRISPR (yet to be approved by relevant regulatory bodies) to generate nitrogen efficient yeast to reduce the need to supplement low nitrogen fermentations.
Thesis (Ph.D.) (Research by Publication) -- University of Adelaide, School of Agriculture, Food and Wine, 2018.

碩士
大葉大學
生物產業科技學系
98
Burkholderia sp. Yu-4 was cultured to produce PHAs by using glucose (as the first carbon source) and organic salts (sodium propionate or sodium valerate as the second carbon source) in a nitrogen-limited medium. A one-time-one-factor method was used to explore the effects of types of nitrogen and carbon sources, organic salts and their concentrations on PHBV biosynthesis and to search for optimal conditions for batch fermentation. From the results of one-time-one-factor experiments using various carbon sources (based on the same amount of carbon in glucose) and ammonium sulfate as the nitrogen source in a flask culture, glucose was the best carbon source, and yields of biomass and PHB reached 4.53 and 1.96 g/L, respectively. When Burkholderia sp. Yu-4 was cultured in various nitrogen sources (based on the same amount of nitrogen in ammonium sulfate) and glucose (as the carbon source), ammonium sulfate was the best nitrogen source to yield the highest biomass (4.90 g/L) and PHB (1.63 g/L). If sodium valerate was added as the second carbon source, the best timing was at 6 h to add this salt. For sodium propionate, the biomass and PHBV production reached 6.02 and 2.38 g/L (HB 2.33 g/L and HV 0.05 g/L), respectively. For sodium valerate, the biomass and PHBV production reached 3.95 and 1.76 g/L (HB 1.52 g/L and HV 0.24 g/L), respectively. When the concentration of organic salt was considered as a factor, the results show that the most appropriate concentration for sodium propionate was 1 g/L, and the biomass and PHBV reached 4.95 and 2.09 g/L (HB 1.95 g/L and HV 0.14 g/L), respectively. For sodium valerate, the most appropriate concentration was 4 g/L, the biomass, and PHBV were 4.93 and 1.98 g/L (HB 1.57 g/L and HV 0.41 g/L), respectively. If no organic salt was added, the optimal PHB production reached 3.95 g/L, and the biomass was 6.47 g/L in a batch fermenter.

Includes author's previously published papers.
"December 2005"
Bibliography: leaves 99-122.
vi, [4], 122 leaves, [43] : ill. (some col.), plates (some col.) ; 30 cm.
Title page, contents and abstract only. The complete thesis in print form is available from the University Library.
Thesis (Ph.D.)--University of Adelaide, School of Agriculture and Wine, Discipline of Wine and Horticulture, 2006

Includes author's previously published papers.
"December 2005"
Bibliography: leaves 99-122.
vi, [4], 122 leaves, [43] : ill. (some col.), plates (some col.) ; 30 cm.
Thesis (Ph.D.)--University of Adelaide, School of Agriculture and Wine, Discipline of Wine and Horticulture, 2006

Nitrogen (N) supply to rain-fed crops is becoming increasingly challenging due to the decline in organic N reserves. In low-rainfall wheat cropping systems, low crop N uptake has been linked to asynchrony in soil N supply through mineralisation. This is especially true on sandy soils of south eastern Australia which have a low N supply capacity and are considered highly ‘risky’ in a management context. When the N released from soil and residues is insufficient, and/or the timing of biological supply is not well matched with crop demand, management of N inputs to the soil (i.e. legume residue addition and/or fertiliser N) is essential to achieve yield potential and to return a neutral soil N balance for environmental sustainability. The general aim of this thesis was to improve our understanding of the seasonal pattern of the soil N supply capacity via mineralisation for increased wheat N uptake and grain yield, by combining N inputs from different crop residues (removed, wheat or lupin) and fertiliser N inputs (nil, or low, or high N) in a low-rainfall sandy soil environment. Field experiments were conducted over 2 years (2015-2016) at low-rainfall Kandosols based on-farm in the Mallee environment of South Australia. The temporal patterns of the soil profile mineral N and plant available water to 100 cm depth, wheat aerial biomass and N uptake were measured in both years (Chapter 2). In 2016 we also measured the disease incidence as a key environmental variable. There was 35 kg ha⁻¹ more soil mineral N to 100 cm depth following lupin compared with wheat residues at the end of the fallow in both years. In a below average rainfall season (Decile 4), wheat biomass produced on lupin residues was responsive to fertiliser N input with soil profile mineral N depleted by increased crop N uptake early in the season. In an above average rainfall season (Decile 9), a higher soil mineral N supply increased actual and potential grain yield, total biomass, N uptake, harvest index and water use efficiency of wheat, regardless of the source of N (legume N/fertiliser N). These experiments showed that the combination of lupin residues with N fertiliser application increased soil profile mineral N at early growth stages, providing a greater soil N supply at the time of high wheat N demand, and the inclusion of a legume in the rotation is critical for improving the N supply to wheat, with added disease break benefits (Chapter 2). The 2016 field experiment involved the quantification of decomposition rates and N release from wheat and lupin residues over the fallow and the subsequent wheat crop growing season with and without fertiliser N application. It also involved measurements of the temporal patterns of the surface soil mineral N, potentially mineralisable N, microbial biomass N, dissolved organic N and with temperature and rainfall as key environmental variables in all treatments (Chapter 3). Residue decomposition and N release over the fallow and the wheat growing season was measured in the field using litterbags with wheat or lupin residues. Fertiliser N input treatments at wheat crop sowing time and surface soil N pools were measured at key growth stages. A higher potential N supply to wheat following lupin residues at early stages was evidenced through greater decomposition rates and N release via mineralisation than wheat residues, which resulted in increased surface soil N pools. This experiment showed that when lupin residues are combined with fertiliser N application, the N supply capacity to wheat is improved during the growing season measured as mineralised N, dissolved organic N and potentially mineralisable N, relative to wheat residues combined with fertiliser N The last experiment (Chapter 4) was conducted under controlled conditions to directly assess (using ¹⁵N labelled fertiliser) the role of N fertiliser on the supply of N to wheat N through soil mineral and biological pools. This experiment measured the role of the N fertiliser combined with wheat, lupin, or no stubble incorporation. Wheat plants were grown in a glasshouse and sampled at 3 critical wheat growth stages (tillering, first node, booting) to determine wheat and ¹⁵N uptake. Soil samples were collected at sowing, tillering, first node and booting to determine mineral N, microbial biomass N, dissolved organic N, and potentially mineralisable N on subsets of samples. This study indicated that the presence of early N immobilisation (between sowing and tillering) in all the treatments without ¹⁵N fertiliser limited N availability for wheat uptake in the subsequent period (between tillering and first node), when fertiliser N appeared critical to maximise N supply for plant requirements. It was found that up to 38% of the ¹⁵N fertiliser applied at sowing was incorporated into the soil microbial biomass pool. Therefore, the fertiliser N was critical to relieve short-term inherent N limitations for both plant and microbial growth, and to supply the longer-term biological pools (microbial biomass) to support subsequent mineralisation potential. This study also showed that reducing the energy limitation to the microbial pool through inputs of carbon from stubble was critical to ensure fertiliser N supplied sufficient N to satisfy plant demand later in the growing period. This research contributes to a greater knowledge of the main factors affecting soil N dynamics relative to wheat N nutrition and yield, quantifying the N supply from soil and fertiliser and the N accumulation in wheat biomass (roots, shoots and grain) at critical phenological stages in a low rainfall sand. Further research will require measurements of the contribution of different legumes combined with varying fertiliser N rates for a complete assessment of the impacts that could be achieved, and examination of the effect on the main soil N pools driving N supply to wheat N uptake across several seasons and/or in different soil types.
Thesis (Ph.D.) -- University of Adelaide, School of Agriculture, Food and Wine, 2020

The biochemical pathways involved in nitrogen (N) utilisation by marine phytoplankton have received considerable attention over the last forty years, but our understanding of these processes, and how they are affected by environmental change is still far from complete. This study investigates N metabolism in marine phytoplankton in both a controlled laboratory environment (using the coastal marine diatom Phaeodactylum tricomutum), and in the open ocean (e.g. Jellicoe Channel and the Subtropical Convergence Zone, New Zealand). Although the characteristics of ammonium uptake have been extensively studied in marine phytoplankton, comparatively little information exists on rates of assimilation. In this study, a robust method for measuring the rate of ammonium assimilation after a transient addition of ammonium is described. The method relies on the measured ability of the protonophore carbonyl cyanide m-chlorophenylhydrazone (CCCP) to release unassimilated ammonium from the cell and prevent further assimilation. There was little or no correspondence between the rate of ammonium assimilation and rates of ammonium uptake or maximum glutamine synthetase (GS) activity in Phaeodactylum tricomutum. Moreover, in N-limited cells maximum GS activity was a poor measure of N incorporation under steady-state conditions. However, GS activity did provide reliable information on N status (e.g. increased GS activity with increased N-limitation). Comparisons of the effects of varying N-source suggest that nitrate-grown cells are not disadvantaged under conditions of N-limitation due to the extra costs associated with nitrate reductase (NR) and nitrite reductase (NiR) activity. The metabolic costs of growth on nitrate may be significantly increased under iron (Fe)-limitation, as both NR and NiR require Fe. Fe-limited chemostat cultures excreted nitrite and ammonium when grown on nitrate. This release is probably a response to insufficient photoreductant under Fe-limited conditions. However, under Fe-limitation cellular N and C was similar to that of Fe-replete cells, suggesting that the N-source used for growth (nitrate or ammonium) did not influence N-assimilation (i.e. that nitrate-grown cells were able to secure the extra reductant required to support growth) under Fe-limited, light saturating conditions. The Gln:Glu ratio (an index of the cellular N-status) was significantly reduced under N-limitation, but not under Fe-limitation. Measurement of several biochemical indicators of the physiological state of phytoplankton cells (e.g. Gln:Glu ratio, GS activity, and Fv/Fm ratio) permitted the nutrient status of phytoplankton populations to be investigated during the NIWA Ocean Fronts programme over the Subtropical Convergence Zone, New Zealand. Low Gln:Glu ratios suggested that phytoplankton in both Subtropical and Subantarctic waters were N-limited, with a marked increase in this ratio when Fe was added to Subantarctic phytoplankton. The temporal utilisation of N by neritic phytoplankton was also investigated in Jellicoe Channel, northeastern New Zealand. Again, several biochemical indicators (e.g. Gln:Glu ratio, GS activity, and Fv/Fm ratio) were used to identify the N-status of this neritic phytoplankton assemblage both during bloom and non-bloom periods.

碩士
大葉大學
生物產業科技學系
97
In this study, sodium valerate was added in a nitrogen-limited medium as the second carbon source (glucose as the primary carbon source) to cultivate strain Yu-3 to produce PHBV (poly-hydroxybutyrate-co-valerate). A preliminary study was performed, one-factor-at-a-time, to investigate the effects of cultivating conditions on the biosynthesis of PHBV. The cultivating conditions included the glucose concentration, timing of adding sodium valerate, and sodium valerate concentration. The results obtained in the method of one-factor-at-a-time were then used in a central composite design to search for an overall optimal condition to produce PHBV. First of all, strain Yu-3 was cultivated with various glucose concentrations(10, 20, 30, 40, 50 g/L). The glucose concentration, 20 g/L, is the best case in which the biomass, PHB and PHV reached 4.29, 0.84 and 0.25 g/L, respectively, and PHB/biomass being 19.58%. When strain Yu-3 was cultivated using sodium valerate as the second carbon source, the best timing of adding sodium valerate was 12 h. The biomass, PHB and PHV reached 6.25, 1.56 and 0.47 g/L, respectively, and the ratio of PHB/biomass was 24.96%. When strain DYU Yu-3 was cultivated with various sodium valerate concentrations (1, 2, 3, 4, 5 g/L), the sodium valerate concentrations, 5 g/L, is the best case in which the biomass, PHB and PHV reached 4.84, 0.29 and 0.76 g/L, respectively, and PHB/biomass being 5.99%. The best result obtained from the one-factor-at-a-time experiments was further examined and used as the center point in a central composite design. Finally, the optimal condition was composed of 19.78 g/L glucose, 7.97 g/L sodium valerate, and the timing of adding sodium valerate at 16.5 h. To validate the above result from the central composite design, an experiment was repeated at the optimal condition. The biomass, PHB and PHV reached 5.22, 0.35 and 0.93 g/L, respectively, and the ratio of PHV/biomass was 17.81% which was in the range of the anticipated interval (18.30±2.93%). The optimal condition was further tested in a batch fermenter. The biomass, PHB and PHV reached 7.31, 0.43 and 2.36 g/L, respectively, and the ratio of PHV/biomass was 32.28%. These results surpass the ones obtained in the flask culture.