As in any animal production industry, disease is inevitable; therefore, it is imperative that aquaculturists are able to effectively manage the disease and maintain their high production levels in an effort to bridge the gap between supply and demand in the seafood industry that has been caused in part by global over-fishing. This management responsibility lies not only in understanding the impact of the treatment on the cultured species, but also in understanding the impact of the treatment to the aquaculture system as an ecosystem. Currently, there is a narrow variety of chemicals approved by either the Food and Drug Administration (FDA) or the Environmental Protection Agency (EPA) for the treatment of disease outbreaks and water quality issues in aquaculture. Approved chemotherapeutants include oxytetracycline, Romet-30®, copper, and formalin. Additionally, a number of chemicals, such as Chloramine-T and potassium permanganate, are used off-label for the treatment of aquaculture systems. In this research, these six more commonly used chemotherapeutants were analyzed for their impacts to the nitrifying bacteria in aquaculture systems. It was found that three of the chemotherapeutants: oxytetracycline, Romet-30®, and chelated copper caused inhibition to the nitrifying bacteria at the whole cell level as demonstrated in the results from water quality and specific oxygen uptake rate analyses. The nitrification process resumed once the chemotherapeutant was removed from the system, either by a mandatory water change or by natural degradation. The other three chemicals: formalin, Chloramine-T, and potassium permanganate did not result in any significant inhibition to the nitrification process. Experiments on laboratory-cultured nitrifying bacteria confirmed these findings. These experiments also resulted in the observation that the expression of amoA was upregulated by the copper exposure and inhibited by oxytetracycline and Romet-30®, but began to resume as the antibiotics degraded. Comprehensively, the findings of these analyses demonstrated that, although nitrifiers are well-known to be sensitive to their environment, the ability of nitrifying bacteria to continue their oxidative processes following exposure to chemical stress is inherent to the bacteria themselves rather than simply occurring under the protection of a biofilm community as has been suggested. / Ph. D.

Bibliography: leaves 183-202

The major objective of this study was to investigate soil ammonia-oxidizing bacterial diversity and composition associated with plant roots of Proteaceae plants and to compare it with non-plant associated soil.

In recent years there has been widespread interest in rearing aquatic organisms of nutritional and commercial value (Calaprice, 1976). The most hopeful prospect for marine prawn culture in the United Kingdom (Wickins, 1976), the Americas (Hanson & Goodwin, 1977) and South Africa probably lies in intensive culture under controlled conditions. A closed system approach, in which a captive body of water is circulated, provides the scope for water quality management which results ~n maximum water utilization and minimal discharge. On the other hand, direct utilization of sea-water in open systems presents problems for aquaculture since this water is subjected to diurnal and seasonal fluctuations in temperature, salinity and turbidity, as well as contamination from industrial, agricultural and maritime sources. Furthermore, large mariculture farms release enormous amounts of organic wastes which result in eutrophication and could lead to environmental deterioration of coastal waters (Gerhardt, 1978). It is well established that circulated sea-water develops an unusual ~on~c composition as a result of the metabolic activity of the prawns and of the nitrifying bacteria in the biological filter. The changes include elevated levels of ammonia, nitrite and nitrate and reduced pH. The presence of even sublethal levels of these nitrogenous compounds ~n closed systems have been found to affect growth of penaeid spec~es (Wickins, 1976). Ammonia and nitrite, which rapidly accumulate in the water, are usually maintained at nontoxic levels by nitrification in the biological filters (Spotte, 1974; Johnson & Sieburth, 1974). The chemolithotrophic bacteria responsible for nitrification are presently classified by their · cellular morphology and by the oxidation of either ammonia and nitrite (Watson, 1974). The predominant ammonia- and nitrite-oxidizing bacteria isolated from natural environments are Nitrosomonas europaea and Nitrobacter winogradskyi, respectively (Watson et aZ., 1981). Direct observation of nitrifying bacteria in natural environments, however, has been limited to studies involving light microscopy with immunofluorescent techniques (Fliermans et aZ., 1974; Fliermans & Schmidt, 1975). The electron microscopic observation of nitrifying bacteria ~sdifficult in natural microcosms with low levels of nitrification and with the presence of sunlight and anaerobic conditions conducive to the enrichment of other bacteria with a similar ultrastructure. However, in closed systems with extremely active nitrification but poor light conditions, the occurrence of morphologically similar forms in numbers that could be easily detected by electron microscopy is unlikely (Johnsort & Sieburth, 1976). Furthermore, the cyst-like colonies of the nitrifiers are unique and are not found with the methane-oxidizing bacteria with a similar ultrastructure (Davies & Whittenbury, 1970; Smith & Ribbons, 1970), whereas the thick cell wall of the cyanobacteria (Carr & Whitton, 1973) and the distinctive cell morphologies of the purple sulphur and purple nonsulphur bacteria (Pfennig, 1967) separate them from the nitrifiers. Therefore, closed systems with active nitrification provide the ideal environment to study the activities of nitrifiers in conjunction with their relative abundance, nature and diversity. In spite of the opportunity offered by closed systems, previous studies (Kawai et aZ., 1965; Wickins, 1976; Gerhardt, 1978; Mevel & Chamroux, 1981) on nitrification have been primarily indirect observations on rates of ammonia and nitrite oxidation to nitrate (Johnson & Sieburth, 1976). Studies on the enumeration and identification of nitrifiers ~n closed systems have been seriously neglected. Kawai et aZ. (1964) included the enumeration of nitrifiers in their study on nitrification while,in a qualitative study, an attempt to identify the in situ nitrifiers 1n closed systems (Johnson & Sieburth, 1976) was not very successful. This study was undertaken to investigate the three basic aspects of nitrification necessary for the understanding of such a process in closed systems, viz., the oxidation of ammonia and nitrite to nitrate, and the enumeration and identification of the nitrifying bacteria. Prior to determining the concentrations of the nitrogenous compounds in the culture water, various methods were evaluated for their accuracy and reproducibility with both sea-water and culture water samples. This approach is necessary in order to gauge the accuracy of results obtained by such methods. Enumeration of nitrifying bacteria was preceded by an investigation on the effect of incubation time on the maximum most probable number , estimate. Such an investigation was necessary because of the inconsistent approach to the enumeration of nitrifiers in previous studies (Wilson, 1927; Walker et al., 1937; Lewis & Pramer, 1958; Molina & Rovira, 1964; Meiklejohn, 1965; Smith et al., 1968). Incubation periods appear to have been chosen arbitrarily in previous investigations. Identifi~ation of nitrifying bacteria necessitates the isolation and purification of these organisms. Isolation of nitrifiers 1S a difficult and time-consuming task (Watson et al., 1981) and could be the main reason for not being included in previous studies on nitrification. Since the success of this study depended upon the isolation and purification of these chemolithotrophs, this aspect is de~lt with in detail. The changes most likely to be associated with nitrification in a closed system were also monitored 1n the culture water. These included pH, dissolved oxygen and biochemical oxygen demand. Apart from a biological sand filter, no other form of culture water treatment was effected during the investigation. The effect of growing the "sugpo" or jumbo tiger prawn, Penaeus monodon (Kinne, 1977) for 22 weeks in a captive body of sea-water was evaluated by comparing the survival and wet mass with those reported by other workers. This study differs greatly from previous reports on nitrification in closed systems because both the "causes" and "symptoms" of this important detoxifying process are investigated. It is intended that the findings of such a study would aid culturists in exploiting the nitrifying potential of closed systems to its utmost. / Thesis (M.Sc.)-University of Durban-Westville, 1984.

The major objective of this study was to investigate soil ammonia-oxidizing bacterial diversity and composition associated with plant roots of Proteaceae plants and to compare it with non-plant associated soil.

Typescript (photocopy) / xxiv, 254 leaves, [71] leaves of plates : ill. ; 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, Dept. of Agricultural Biochemistry, 1982

Thesis (Ph. D.)--University of Adelaide, Dept. of Agr. Biochemistry, Waite Agr. Research Inst., 1984. / Includes bibliographical references (leaves 183-202).

Thesis (Ph. D.)--Oregon State University, 2008. / Printout. Includes bibliographical references (leaves 120-137). Also available on the World Wide Web.

Thesis (Ph.D.) -- University of Adelaide, Dept. of Agricultural Biochemistry, 1982. / Typescript (photocopy).

Thesis (Ph.D)--Murdoch University, 2008. / Thesis submitted to the Faculty of Sustainability, Environmental and Life Sciences. Includes bibliographical references (p. 213-220).