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Title: Carbon metabolism and growth of marine unicellular cyanobacteria belonging to the genus Synechococcus
Author: Howard, Katharine Mary
ISNI:       0000 0001 3582 5043
Awarding Body: University of Warwick
Current Institution: University of Warwick
Date of Award: 1990
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An investigation was made into the carbon metabolism of the marine unicellular cyanobacterium, Synechococcus sp., strain WH7803, in laboratory cultures and natural populations. Synechococcus WH7803 grown in continuous culture, was used to study the effect of different irradiances (10 - 90/iEm‘2s"1) on the growth and photosynthetic characteristics of the organism. Growth saturated at relatively low irradiances (@55/iEm'2s'r). Parameters were measured for photosynthetic relationships, pigment concentrations and total quantities of DNA, RNA and protein present in the cells. Although the photosynthetic maximum was highest in cultures grown at high irradiances, alpha (initial slope) was steeper in low light-grown cultures indicating a higher photosynthetic efficiency in these cultures. The assays for DNA, RNA and protein were used to establish a general pattern of response under the different light conditions. Respiratory rates of batch cultures were measured at different irradiances and the heterotrophic potential of these cultures was tested using an oxygen electrode. No significant alteration in the respiratory rate was observed for a range of organic compounds added to growing cultures in the dark. Trials with two inhibitors to remove heterotrophic microbial activity from natural populations proved insufficiently sensitive for further use. Three studies of natural populations from the North Sea and Celtic Sea were carried out to determine the abundance and distribution of Synechococcus species, and to measure their rates of photosynthesis and other physiological/ ecological properties compared to other phytoplankton. As with laboratory cultures the data indicate that natural populations utilise low irradiances efficiently; however Synechococcus sp., have been found to be equally abundant and productive in the surface mixed layer where they experience high irradiances (1700/iEm*2s‘1). Cellular fractionation of ^C labelled samples was used to determine the physiological consequences of growth at high irradiances. In laboratory cultures the percentage 14C incorporated into protein remains high (@50%), at high and low irradiances, whereas incorporation into the polysaccharide and nucleic acids was typically higher at high irradiances. In natural assemblages the percentage incorporation into protein remained high (@55%) and into polysaccharide and nucleic acids relatively low at @17%. In natural assemblages significantly more label was detected in the lipid fraction.
Supervisor: Not available Sponsor: Natural Environment Research Council
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: QR Microbiology