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Title: Physiology and biochemistry of N2 fixation in Trichodesmium and Lyngbya ssp UCS825
Author: Richardson, M.
Awarding Body: University of Wales Swansea
Current Institution: Swansea University
Date of Award: 1999
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The marine, filamentous, non-heterocystous cyanobacteria, Trichodesmium and Lyngbya sp. UCSB25, are very similar. Both can fix N2 aerobically. However, Trichodesmium differs from Lyngbya sp. UCSB25 and almost all other non-heterocystouc diazotrophs in that it fixes N2 during the day whilst simultaneously photosynthetically evolving O2. In contrast, Lyngbya sp. UCSB25 and most other non-heterocystous cyanobacteria, perform N2 fixation during the night. During laboratory growth, Trichodesmium sp. IMS 101 effects a temporal separation between maximal rates of N2 fixation and net production of O2. Thus, peak nitrogenase activity occurs simultaneously with net consumption of O2. The same is true of Lyngbya sp. UCSB25. Addition of exogenous ammonium (NH4+), but non nitrate (NO3), inhibited nitrogenase activity of natural populations and laboratory cultures of Trichodesmium. As in other diazotrops, inhibition caused by NH4+ depends upon its assimilation through the GS-GOGAT pathway. A 30min thermal shock, of 36°C or 40°C to Trichodesmium and Lyngbya sp. UCSB25, respectively, caused a 75% inhibition of nitrogenase activity. In Lyngbya sp. UCSB25 this effect is probably exerted through an inhibition of one or more, kinetically distinguishable O2 uptake system. In Trichodesmium the basis of inhibition was more probably due to a lesion(s) in general metabolism that was independent of O2. Ascending and descending colonies of natural populations of Trichodesmium show dramatic biochemical differences. Results obtained after the addition of either DCMU or CN suggest that nitrogenase activity in ascending and descending colonies is reliant on respiration and photosynthesis, respectively.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available