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Sandbox 1

Phylogeny
 Domain  – Bacteria

The Tree of Life contains three Domains: Bacteria, Archaea, and Eukarya.

 Kingdom  – Bacteria

Bacteria consists of prokaryotic microorganisms. They were among the first life forms to appear on Earth and appear in a wide variety of habitats.

 Phylum  – Cyanobacteria

This phylum is characterized by their ability to obtain energy through photosynthesis. They are often called the blue-green algae stemming from the Greek origins of the word kyanós, meaning blue.

 Class  – Cyanophyceae

This class consists of photosynthetic bacteria found in fresh and salt water, containing chlorophyll a and phycobilins.

 Order  – Nostocales

This order includes cyanobacteria of filamentous forms, either simple or branched, both of which occur as single strands or multiple strands within a sheath.

 Family  – Nostocaceae

This family of cyanobacteria forms filament-shaped colonies enclosed in mucus or a gelatinous sheath. Their habitats vary widely ranging from fresh water to salt water conditions. They often contain photosynthetic pigments in their cytoplasm to perform photosynthesis, which gives the cells a bluish-green color.

 Genus  – Cylindrospermopsis

This genus of filamentous cyanobacteria is found in terrestrial and aquatic environments. In terrestrial ecosystems, Cylindrospermum is found in soils, while in aquatic it commonly grows as part of the periphyton on aquatic plants. The particular genus is a heterocystous (nitrogen-fixing) cyanobacterium.

 Species  - Cylindrospermopsis raciborskii

Nitrogen-Fixation Pathway
C. raciborskii is a filamentous cyanobacteria with the ability to fix nitrogen by converting atmospheric nitrogen (N2) into ammonia (NH3) . This process provides the cells in the filament with nitrogen for biosynthesis; the reaction depends on the enzyme nitrogenase. Normally, nitrogenase is inactivated by oxygen, which forces the bacterium to operate in a microanaerobic environment. Nitrogen fixation is also facilitated by heterocysts. The heterocyst’s unique structure and physiology requires a global change in gene expression. This includes a variety of mechanisms including, but not limited to:


 * Producing three additional cell walls, including one of glycolipid that forms a hydrophobic barrier to oxygen
 * producing nitrogenase and other proteins involved in nitrogen fixation
 * the degradation of photosystem II, which produces oxygen
 * up-regulation of glycolytic enzymes
 * producing proteins that scavenge any remaining oxygen
 * containing polar plugs composed of cyanophycin which slows down cell-to-cell diffusion

C. raciborskii obtains its fixed carbon via photosynthesis. The lack of photosystem II in heterocysts would normally prevent photosynthetic carbon fixation, but the vegetative cells provide the necessary carbohydrates, which are thought to be mostly sucrose. The fixed carbon and nitrogen are exchanged between heterocysts and vegatative cells through channels between the cells in the filament. C. raciborskii does maintain photosystem I in its heterocysts, allowing it to generate ATP by cyclic photophosphorylation.

The mechanism of controlling this nitrogen fixation pathway is thought to involve the diffusion of an inhibitor of differentiation called patS. Heterocyst formation is inhibited in the presence of a fixed nitrogen source, such as ammonium or nitrate. Therefore, maintenance is dependent on an enzyme called hetN. An alternate method involves the bacteria entering a symbiotic relationship with certain plants. In such relationships, the bacteria does not respond to the availability of nitrogen, but rather to signals produced by the plant. In this method, up to 60% of the cells can become heterocystsic, providing fixed nitrogen to the plant in return for fixed carbon.

Pathogenesis
The appearance of cyanobacteria in water storage bodies is becoming of increasing importance and is a major factor in the eutrophication of rivers and streams. In many instances the presence of C. raciborskii can be toxic for livestock and wildlife, as well as for humans .

Palm Island Incident
In 1979, C. raciborskii was blamed for causing hepatoenteritis (an infection of the liver resembling hepatitis) in 148 people off the northern coast of Queensland at Palm Island. The contamination of drinking water was attributed to copper sulfate treatment in the island’s drinking-water supply, Solomon Dam. The copper sulfate was intended to control a dense algal bloom. However, copper sulfate causes lysis of cyanobacteria, leading to the release of any toxic cellular components. It was determined after an investigation that the contaminated water was all from Solomon Dam where the copper sulfate was applied. It was during this investigation that C. raciborskii was first identified as a pathogen.