Thesis (Ph. D.)--University of Hong Kong, 1999. / Includes bibliographical references (leaves 218-268).

Thesis (Ph. D.)--University of Alabama at Birmingham, 2008. / Title from first page of PDF file (viewed Sept. 22, 2008). Includes bibliographical references (p. 116-128).

Microalgae are promising candidates for biofuel production, CO2 biomitigation, and production of a variety of value-added products. However, high production costs and large energy consumption have been a major concern hindering the commercialization of microalgal products and processes. In addition, biological contamination and oxygen stress are two of the major contributors to these challenges. The objective of this project was twofold: 1) developing a novel strategy for control of biological contamination to enable non-sterile cultivation of microalgae such as N. oleoabundans, and 2) developing advanced deoxygenation mechanisms to reduce oxygen accumulation in the culture. It was found that addition of appropriate amount of NaHCO3 could effectively inhibit the growth of protozoa while its inhibition on microalgae was much less and could be alleviated by increasing pH to an appropriate level. It was also found that adding 160 mM NaHCO3 in media or decreasing incident light intensity to 100 W/m2 would help alleviate the oxidative stress to cells at 400% of air saturation. The feasibility of contamination-free non-sterile cultivation of freshwater green alga N. oleoabundans was verified using long-term continuous cultivation in a 15-liter TPBR with non-sterile medium and aeration. Furthermore, localized oxygen removal using hydrophobic hollow membranes was found to effectively reduce dO2 and increase lipid accumulation. These results have the potential to be translated into low-cost cultivation of freshwater microalgae processes for production of value-added microalgal products. At a more fundamental level, the mechanisms of the inhibition of NaHCO3 on microalgae and protozoa were discussed. Efforts were also made to simulate the effects of incident light intensity on light distribution, cell growth kinetics, and lipid accumulation of N. oleoabundans under non- sterile cultivation conditions.

Low substrate regulated microaerophilic behavior (LSRMB), as measured by changes in microaerophilic band formation in semi-solid medium, was observed in several aerobic bacteria isolated from subsurface soils, Antarctic dry valley soils, an eutrophic pond, a mesophilic pond, an oligotrophic lake and activated sludge. Similar behavior was also exhibited by five Pseudomonas and two Bacillus type strains from culture collection. Isolates identified with LSRMB formed a typical band of growth below the surface of low substrate (10 mg/l of peptone, tryptone, yeast extract and glucose) semi-solid medium. Surface growth was obtained when the substrate concentration was increased (1000 mg/l of each of the above mentioned substrates). LSRMB was observed in phylogenetically disparate groups, with all the Pseudomonas and two Bacillus species testing positive for the trait. One of the Gram-negative isolates, strain VT10, was identified by phylogenetic analysis based on its 16S rDNA sequence. High 16S rDNA sequence similarity (99%) was observed with the recently discovered Pseudomonas jessenii (CIP 105274T) type strain. Strain VT10 was used as a model to examine this LSRMB, and show the relationship between oxygen stress and low-substrate growth media. The concentration of 17:0 cyclopropane fatty acid, a common stress indicator, increased 5-fold, and four additional proteins were produced when P. jessenii strain VT10 was grown at low-substrate levels and when the dissolved oxygen concentration was increased from 26 microM to 241 microM. The stress responses by P. jessenii could be due its LSRMB. This study shows that low-substrate regulated microaerophilic behavior helps some microorganisms to track the oxygen minima in their habitat and thus effectively move to an environment, which allows them to thrive. In addition to the above mentioned taxis in response to oxygen concentration, organisms may use chemotaxis to a chemical compound. Quantification of chemotaxis can be extremely difficult. To quantify chemotaxis in an easier fashion, a simplified capillary chemotaxis assay, utilizing a hypodermic needle, syringe and disposable pipette tip was developed. The method was applied to two strains of subsurface microaerophilic bacteria. Strain VT10 was chemotactically attracted toward dextrose, glycerol, and phenol, which could be used as sole carbon sources, and toward maltose, which could not be used. The deep subsurface isolate MR100 (phylogenetically related to P. mendocina) showed no tactic response to these compounds although it could use dextrose, maltose, and glycerol as carbon sources. The chemotaxis results obtained by the new method were verified by using the swarm plate assay technique. The simplified technique may be useful for routine chemotactic testing. / Ph. D.

Sessile invertebrates in the rocky intertidal experience intermittent periods of air exposure due to tidal flux, presenting risks of temperature extremes, hypoxia, nutrient limitation, and most dangerously, desiccation. Microscale variation in severity and frequency of these risks is widely dependent on vertical position within the intertidal zone. Common acorn barnacles (Balanus glandula) have a wide vertical distribution in the intertidal, creating large differences in microhabitat between the highest and lowest individuals in the population. This study set out to explore whether tidal position dependent differences exist in the response to oxygen and desiccation stress in B. glandula. We hypothesized that B. glandula from relatively high tidal heights, which are exposed to the air for a greater duration, will be better suited to tolerate anoxic and desiccation stress than conspecifics from lower tidal heights. To explore this, we compared responses of B. glandula collected from high and low intertidal positions to A) anoxia (0 mg O2/L) and hypoxia (≤ 2 mg O2/L) on survival, behavior (closed opercular plates, cirral beating, pneumostome formation), enzyme activity (lactate dehydrogenase (LDH), superoxide dismutase (SOD)), and tissue-lactate accumulation, in addition to B) the effects of humid (98% RH) and dry (32% RH) air emersion (at 17˚C) on survival, opercular behavior (open/closed), evaporative water loss (EWL) rates, and tissue-lactate accumulation. Relative to barnacles from the low intertidal, we found that barnacles from the high intertidal survive longer during anoxia and air emersion stress, close their operculum sooner in dry air, lose more water during air exposure at any humidity level, and tend to accumulate less D-lactate. We suspect that high intertidal B. glandula can survive desiccation longer by ejecting stores of mantle cavity fluid, thereby creating a moist lung-like, air-filled internal environment, then remaining largely closed and metabolically inactive when in air to avoid drying out and becoming anoxic. These differences may reflect plasticity or selective pressure in response to environmental stress during development and highlight the potential importance of microscale stress heterogeneity in influencing species climate change tolerance and potential distribution patterns.