Nostoc

Cross Index	Nostoc
SuperSet	Prokaryote, Eubacteria Oxygenic Phototrophic Bacteria
Compare	Cyanobacteria Chroococcales: Chamaesiphon, Cyanothece, Gloeobacter, Gleocapsa, Gloethece, Microcystis, Myxobaktron, Synechococcus, Synechocystis Pleurocapsales Chroococcidiopsis, Dermocarpa, Dermocarpella, Myxosarcina, Pleurocapsa, Xenococcus Oscillatoriales Arthrospira, Crinalium, Lyngbya, Microcoleus, Oscillatoria, Pseudoanabaena, Spirulina, Starria, Trichodesmium Nostocales Anabaena, Aphanizamenon, Cylindrospermum, Nodularia, Nostoc, Scytonema, Calothrix Stigonematales Chlorogloepsis, Fischerella, Geitleria, Stigonema Prochlorales Procloron didemni, Prochlorothrix hollandica
Contrast	Anoxygenic Phototrophic Bacteria Archaea
Subset

Morphology

Nostoc

CELLULAR

Staining
Morphology
Motility	vegetative trichomes are not capable of gliding motility. However, short chains of cells (hormogonia) are formed and released. These, usually motile trichomes are initially located adjacent to a heterocyst or between two heterocysts but lack heterocysts themselves. The hormogonia cease movement after a period of "migration", at which time two terminal heterocysts are differentiated.
Specialized structures	The trichomes are untapered with conspicuous constrictions at cross-walls. The cells are cylindrical, spherical or ovoid (barrel-shaped) and are not shorter than broad. Heterocysts are intercalary under most circumstances Gas vesicles occur in the vegetative cells of several species of Nostoc, although few colonies are buoyant enough to be planktonic. Nostoc is,distinguished (in the absence of colony formation) by the presence of a developmental cycle. Cell division and growth then resume; this is accompanied by gel formation under feral and some culture conditions (Lazaroff, 1973). The cell width of hormogonia is commonly less than that of the vegetative trichomes; often hormogonia are gas-vesiculate and buoyant when the vegetative trichomes are not. These latter characteristics may be sufficient to distinguish this stage (hormogonium) even when motility is not apparent (as in some culture strains).

Division

trichomes of old cultures commonly break up into unicells. Detached unicells commonly occur in masses in developing colonies or in symbiotic associations as well.

COLONIAL

Solid surface

Nostoc (sensu Geitler) is characterized by a confluent gel holding masses of trichomes together, often in the form of a massive thallus which may be spherical, ovoid or of a less discernible shape. Some colonies or thalli take the form of flattened disks or large sheets or may be soft and amorphous. In many cases, the outer layer of the colony is firm and contains most of the trichomes, while the interior layer is a soft gel with few trichomes which may be radially arranged The size of colonies range from microscopic (originating from a single hormogonium come to rest) to over 20 cm in diameter. However, Rippka et al. (1979) consider the formation of a gelatinous colony to be a secondary character, since in culture, some strains do not form gel and a thallus

Liquid

In many cases, the semispherical colonies are not attached but rest lightly on firm or unconsolidated sediments

Growth Parameters

Nostoc

PHYSIOLOGICAL

Tropism	Of the 13 strains examined by Rippka et al. (1979), only 3 were unable to grow as photo-heterotrophs. Several species and strains of Nostoc grown elsewhere are known to grow slowly as dark chemoheterotrophs (Lazaroff 1973
Oxygen
pH
Temperature
Requirements
Products	A few have apparently lost the ability to fix nitrogen aerobically despite the presence of heterocysts.
Enzymes
Unique features

ENVIRONMENTAL

Habitat	Various species of Nostoc are known from benthic habitats in freshwater lakes and springs Some species are attached to solid substrate in lakes or streams. Many species of Nostoc occur as amorphous sheets or masses of gel-bound trichomes in freshwater or in moist terrestrial locations.
Lifestyle	As a symbiont, Nostoc is the major phycobiont in cyanolichens, but it also occurs as the N2-fixing symbiont in tripartite, cephalodiate lichens and in several embryophytes such as bryophytes, cycads, and the angiosperm genus Gunnera
Pathogenicity

Distribution

Nostoc is known to form thick, soft masts in polar regions where presumably it is a major contributor of fixed nitrogen

Genome	Nostoc
G+C Mol %	13 strains of Nostoc ranges from 39 to 45 (Herdman et al. 1979a), although several species are probably represented by this assortment.

The genome size of 11 of these strains ranges from 4.00 to 6.42 x 109 daltons (Herdman et al. 1979b).

Reference	Nostoc
First citation	Vaucher,J.P. 1803. Histoires des conferves d'eau douce, contenant leurs different modes de reproduction, et la description de leurs principales especes. J. Paschoud. Geneva pp 1-285.
The Prokaryotes
Bergey's Systematatic	p 1788 R.W. Castenholz
Bergey's Determinative	p 405
References