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Title: Heterotrophic activity in marine waters
Author: Diwan, H. R.
Awarding Body: University College of Swansea
Current Institution: Swansea University
Date of Award: 1978
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An attempt was made to compare the rates of primary productivity and of microheterotrophic activity in th waters of Swansea Bay. In order to do this, primary productivity was measured by the 14C fixation method, and chlorophyll a content of the water was used as a measure of phytoplankton biomass. Estimations of microheterotrophic activity and of microbiol biomass were based on the measurement of rates of glucose uptake and of ATP in the water after detailed examination of the applicability of these methods. Estimation of ATP was based on the measurement, in a scintillation counter, of the light produced by a cell-free fire-fly bioluminescence system. Several variants of this method were tried. The one finally adopted was based on the method of Stanley and Williams (1969) and was capable of estimating 2.4 ng ATP per litre seawater. The values found in the seawater samples ranged from 2 to 300 ng per litre. Rates of glucose uptake were estimated by measuring rates of uptake of added 3H-glucose of high specific activity coupled with measurements of the concentration of glucose naturally present on the water samples. It was shown that, under the incubation conditions used, rate of 3H-glucose uptake was linear with time and proportional to the quality of unsterilized seawater present. From these estimations, values for the turnover time of glucose were obtained. These were 1-2 days in May/June, 3-9 days in April/May and about 30 days in August. In order to obtain absolute rates of glucose metabolism it was necessary to measure the concentration of the glucose naturally present in the seawater. Several methods of doing this were tried and the one finally adopted was based on the fluorimetric enzymatic assay of Hicks and Carey (1968). In this glucose is coupled with the enzymes hexokinase, glucose-6-phosphate dehydrogenase and diaphorase with the dyeresazurin so that the dye is reduced to the highly fluorescent resarufin. After some difficulties this method was applied successfully to measurements of glucose in the waters of Swansea Bay. Values ranged from 1-80ug/l. Using these values, and the rates of H-glucose uptake measured in the same samples, rates of glucose uptake were estimated at 0.004 to 0.98og glucose/l/hour. During June to October, 1977, samples were taken at intervals from Mumbles Pier and 3 miles off-shore in Swansea Bay. Using these samples, rates of primary productivity and of microheterotrophic activity were measured together with the ATP, glucose and chlorophyll a content of the water. Certain trends in these parameters with time were distinguished and are discussed. There is some evidence that suggests that rate of glucose uptake may be determined by the glucose content of the water and that, this in turn, may be determined by rate of primary productivity. Rates of glucose metabolism were, however, low in comparison with rates of primary productivity. In terms of carbon flux glucose uptake was generally less than 1% of carbon fixation by photosynthesis. It is concluded that measurement of glucose uptake may be an inadequate indicator of total microheterophic activity.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available