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Title: Studies on the diurnal pattern of N2 fixation by cyanobacteria
Author: Griffiths, M. S. H.
Awarding Body: University College of Swansea
Current Institution: Swansea University
Date of Award: 1988
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Nitrogenase activity was observed in-situ at two sites dominated by cyanobacteria: Landimore Marsh, Gower, where the diazotroph was on Oscillatoria sp, and Cathole Cave, Gower where the diazotrophic species were Nostoc sp and Gloeothece sp. These sites were surveyed throughout the course of 12 months. The diurnal patterns of nitrogenase activity observed in-situ at each site were found to be characteristic of the cyanobacteria present, and to be identical to the patterns exhibited by laboratory cultures. No activity was observed at either site during the three coldest months of the year, November, December and January. In-situ, and in the laboratory, low temperatures proved to have a greater effect on nitrogenase activity than daylength or light intensity. Nevertheless, in the laboratory lengths of light period below 8-10h out of 24h were found to limit growth by cyanobacterial cultures, N2-fixing or otherwise. In cultures of Gloeothece or Scytonema maintained under alternating light and darkness N2 fixation in the dark increased markedly as the light intensity during the light period was increased from 5 to 80 uE/m2/s. In addition, these cyanobacteria proved better able to withstand high light intensities under alternating light and darkness than under continuous illumination. In Gloeothece temperatures of 37oC or above were found to be inhibitory to both nitrogenase activity and growth. This inhibition was not observed under anaerobic or microaerobic conditions. It therefore appeared that the inhibition was not due to an effect on nitrogenase itself, but rather to an effect on a mechanism for protecting nitrogenase against O2-inactivation. The patterns of acetylene reduction by cyanobacterial cultures maintained under alternating light and darkness, were unaffected by immobilization in agar cubes, alginate beads, or polyvinyl foam cubes. Furthermore, mixed populations which were unstable in liquid culture, were readily maintained in immobilized cultures.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available