Title page for ETD etd-06042008-145600
|Type of Document
||Horn, Kevin J.
|Author's Email Address
||The Effect of Nitrates, pH, and Dissolved Inorganic Carbon Concentrations on the Extracellular Polysaccharide of Three Strains of Cyanobacteria Belonging to the Family Nostocaceae
||Master of Science In the Life Sciences
|Helm, Richard Frederick
|Larson, Timothy J.
- carbon-nitrogen ratio
- extracellular polysaccharide (EPS)
|Date of Defense
Three strains of cyanobacteria (Anabaena PCC7120, A. variabilis and Nostoc commune), all
belonging to the family Nostocaceae, were found to be capable of modulating the production and
chemical composition of extracellular polysaccharides (EPS) in response to carbon and nitrogen
availability as well as pH. While the carbohydrate compositions of the glycans produced by the
different organisms were indicative of their recent evolutionary divergence, there were
measurable differences that were dependent upon growth conditions. The EPS resulting from
biofilm growth conditions was reduced in glucuronic acid levels in both Anabaena variabilis
ATCC 29413 and Anabaena PCC 7120. Under planktonic conditions, the glycan from A.
variabilis contained glucuronic acid when grown in nitrate-free BG-110 medium whereas A. PCC
7120 produced similar levels in standard BG-11 medium. This suggests that phylogeneticallyrelated
cyanobacteria respond very differently to changes in their local environment. The pH of
BG-11 cultures increased to 9-10 for all three strains of cyanobacteria. The increase resulted in
an increase in the amount of dissolved inorganic carbon available in the medium, creating an
imbalance in the carbon-nitrogen ratio, with the complete consumption of 17.65 mmol L-1
nitrates raising the pH to near 10 in BG-11 medium. While increased carbon availability has
been shown to induce capsulated morphologies in strains of cyanobacteria, only Nostoc
commune DRH-1 exhibited this behavior, and only when grown in BG-11 medium.
Carbon and nitrogen availability as well as pH modulate the monosaccharide composition
of the glycan generated by cyanobacteria investigated. The different characteristics of the
glycans produced can affect the survivability of the organisms and the community structure of
cyanobacterial biofilms and microbial mats found in nature. As cyanobacteria are ubiquitous
organism both now and in the past, they play a pivotal role in the biological and geological
processes of the Earth, controlling the availability and cycling of carbon and nitrogen both
actively and passively.
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