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Title: Genes involved in nitrogen fixation and heterocyst differentiation in Anabaena sp. PCC 7120 
Author: Yamaura, Hiroshi
Date: 2006
Abstract: Cyanobacteria, also commonly known as blue green algae, emerged approximately 3.5 billion years ago as the first photosynthetic prokaryotes on Earth. Accumulation of oxygen generated as a byproduct of their photosynthetic activity changed the nature of the primitive atmosphere from anoxic to oxic, leading to the evolutionary transition that resulted in the emergence of aerobic organisms and consequently in the rise of higher plants and animals that predominate the ecosystems in today's biosphere. In addition to generation of oxygen, cyanobacteria have also been of considerable importance for their role in fixing atmospheric dinitrogen to produce other forms of nitrogen, such as ammonium, that is utilizable to other organisms. Many of the free-living and symbiotic cyanobacteria contribute significantly in fertilizing aquatic and terrestrial environments with their ability of nitrogen fixation, sustaining growth and prosperity of a wide range of populations in those habitats. Study of cyanobacteria, therefore, has been an intensive area for their significant ecological roles in various ecosystems. Perhaps of equally important reason for the growing popularity of studying cyanobacteria comes from the fact that they are the first filamentous multicellular organisms that appeared on Earth. In addition, they also exhibited cellular differentiation to form heterocysts, cells specialized for nitrogen fixation. Production of oxygen caused by photosynthetic activity of cyanobacteria imposed a problem on nitrogen fixation, which is mediated by nitrogenase, an enzyme extremely sensitive to oxygen. Evolution of oxygen would inevitably inactivate nitrogenase, with both oxygen and nitrogenase being present intracellularly. Some species of cyanobacteria evolved a temporal separation of photosynthesis and nitrogen fixation, carrying out the former during the day and the latter at night Some other species, such as Anabaena, produced differentiated cells called heterocysts, which do not perform the oxygen-evolving part of photosynthesis and form extra layers of an envelope to prevent oxygen diffusing into the cell, creating an ideal microaerophillic environment for nitrogenase activity. A fixed form of nitrogen produced in heterocysts in a filament then is distributed to the photosynthesizing cells so the filament as a whole does not starve for nitrogen while still capable of photosynthesis. For efficient distribution of a fixed source of nitrogen from heterocysts to photosynthesizing cells, or more commonly called vegetative cells, heterocysts are evenly spaced in filaments. The genera of cyanobacteria forming the two distinct types of cells demonstrate a one-dimensional pattern of multicellularity between the two different cell types, providing the simplest example of pattern formation and developmental regulation. A series of technological breakthroughs in molecular biology in the past decades have been enabling approaches on molecular and genetic levels to elucidate complex mechanisms governing cellular differentiation and pattern formation in some species of cyanobacteria. In this study, mechanisms governing nitrogen fixation, cellular differentiation, and pattern regulation in Anabaena sp. PCC 7120, a filamentous cyanobacterium capable of forming heterocysts in a regulated pattern, were examined and reported.
Description: Thesis (M.S.)--University of Hawaii at Manoa, 2006. Includes bibliographical references (leaves 45-57). vi, 57 leaves, bound ill. 29 cm
URI: http://hdl.handle.net/10125/20727
Rights: All UHM dissertations and theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission from the copyright owner.
Keywords: Anabaena -- Genetics

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