Nostoc punctiforme
A Microbial Biorealm page on the genus Nostoc punctiforme
Classification
Higher order taxa
Domain: Bacteria
Phylum: Cyanobacteria
Order: Nostocales
Family: Nostocaceae
Species
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NCBI: Taxonomy |
Genus : Nostoc
Species : punctiforme
Description and significance
Describe the appearance, habitat, etc. of the organism, and why it is important enough to have its genome sequenced. Describe how and where it was isolated. Include a picture or two (with sources) if you can find them.
Genome structure
Nostoc punctiforme has one of the largest sequenced bacterial genomes to date. It larger than any of the other sequenced cyanobacterial genome, with an astounding current base count of 9,757,495 (3). The enormity of the genome is necessary for the cell to be able to adapt to numerous drastically different environments. It is a circular genome that consists of 45.2 mol % Guanine and Cytosine pairs and 54.8 mol % Adenine and Thymine pairs (4). Each cell contains multiple copies of the circular chromosome (5) which is hypotheisezed to be one of the reasons that N. punctiforme are able to withstand DNA mutagenisis due to prolonged exposure to UV light (6).
Of the 5000 recognized open reading frames (ORFs), 62% encode for proteins with a known or probable function. Curiously enough, one fourth of the genome encodes ORFs that cannot be associated with any previously sequenced ORF. Of the recognized ORFs, 5%, the largest proportion of genes, code for signal transduction mechanisms which can be understood by the cell’s extensive ability to sense and respond to environmental factors. Cell envelope synthesis, cell division and chromosome segregation account for 4% of the ORFs, as do amino acid transport and metabolism. Organic carbon metabolism codes for 3% of the ORFs (3). Apart from the coding DNA, the genome for N. punctiforme has been found to contain numerous insertions sequences and multilocus repeats as well as genes that code for transposase and DNA modification enzymes (2). These are characteristics that contribute to the genomic variation within the species.
Cell structure and metabolism
Nostoc punctiforme is capable of survivng in radically different environments. In order for it to be able to do this, it must be capable of multiple metabolic pathways. N. punctiforme is usually an autotroph, however it can behave as a heterotroph if it is concealed from light for an extended period of time (3). In this state, the cell relies heavily on the oxidative pentose phosphate pathway. In more standard conditions that provide available light, the cell has not only chlorophyll a (standard in most autotrophs), but also light harvesting pigments which allow it to thrive in competitive habitats or in cases of constant UV light (2).
Of all the metabolic processes it is capable of, N. punctiforme is most recognized for its efficient nitrogen fixation capablilities. It can utilize various inorganic and organic nitrogen sources which reduces its competition in its habitat. However, when nitrogen sources are poor or nonexistant, N. punctiforme will begin heterocyst differentiation, the first of three possible cellular forms for the prokaryote. This results in the termination of oxygenic photosynthetic reactions and conversion to heterotrophic metabolic mode. There will also be a sharp increase in respiration rate(3). In this state, the cells are 6-10 mm in diameter (4). In an environment where there is a limitation on nutrient sources other than nitrogen, the cell will convert into a spore, which for this particular species is known as an akinete. In an akinete form, with a diameter between 10 and 20 mm(4), the bacteria can reamain viable for hundreds of years. However, there is little information on their metabolic pathways at this time. The third potential form for N. punctiforme takes place under high stress. When this occurs, the cell takes on the form of a hormogonium filament. In this state, the cells will undergo division without the usual precursors of an increase in cell biomass and DNA replication. These cells become motile filamens that express photo and chemoactic behaviors. They also produce gas vesicles in order to create buoyancy in soil or water(3). The homogonium filaments are 1.5 to 2 mm in diameter (4).
N. punctiformes ability to differentiate between cell structures and accommodate metabolic pathways accordingly is the reason it is one of the most versatile and adaptatious microbes understood today.
Ecology
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Pathology
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Application to Biotechnology
Does this organism produce any useful compounds or enzymes? What are they and how are they used?
Current Research
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References
Edited by student of Rachel Larsen
