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Nostoc punctiforme ATCC 29133
   
   
 

"Heterocysts in vegetative filaments."
Nostoc punctiforme is a nitrogen-fixing cyanobacterium belonging to the family Nostocaceae in the order Nostocales (Castenholz and Waterbury, 1989). All cyanobacteria are characterized as eubacteria that grow as autotrophs with CO2 as the carbon source, utilizing an oxygen-producing photosynthetic mechanism for the generation of ATP and reductant. Members of the order Nostocales are broadly characterized by growth as unbranched filaments and the production of up to three kinds of differentiated cells. Heterocysts differentiate in response to the lack of combined nitrogen in the environment and are the sites of nitrogen fixation. Heterocysts occur singularly in a semi-regular spacing pattern in the filaments at a frequency of 3 to10 % of the total cells (panel A). Nostoc species also produce relatively short, motile filaments called hormogonia (panel B) and this characteristic, in part, distinguishes them from members of the closely related genus Anabaena. In addition, Nostoc species differentiate spore-like structures termed akinetes in response to nutrient limitation other than nitrogen (panel C). Nostoc species are widely distributed in illuminated portions of the biosphere, including fresh waters and tropical, temperate and polar terrestrial systems; they are rarely found in marine habitats (Potts, 2000). Growth in both aquatic and terrestrial habitats is often as a colony of filaments within a gelatinous matrix (Dodds et al., 1995). The size of the colonies ranges from microscopic to macroscopic dimensions. Many Nostoc species occur in symbiotic associations with fungi to form lichens and with representatives of each of the major phylogenetic groups of plants (Meeks, 1998). Nitrogen-fixing Nostoc species, in both free-living and symbiotic growth states, are major contributors to the sequestration of CO2 in organic compounds, especially in nutrient poor and extreme environments.

N. punctiforme strain ATCC 29133 (deposited in the ATCC from the original PCC 73102 culture) has a complex life cycle in the differentiation of heterocysts, hormogonia and akinetes. The vegetative cells are 5 to 6 m m in diameter, hormogonium cells 1.5 to 2 m m, heterocysts 6 to 10 m m and akinetes 10 to 20 m m. The strain was isolated from symbiotic association with the gymnosperm cycad Macrozamia sp. (Rippka and Herdman, 1992). In the laboratory, N. punctiforme 29133 will reconstitute an extracellular symbiotic association with the bryophyte hornwort Anthoceros punctatus and an intracellular association with the herbaceous angiosperm Gunnera spp. (Meeks, 1998). As one of a small subset of cyanobacteria, N. punctiforme grows rapidly under completely dark heterotrophic conditions, with sucrose, glucose or fructose as the carbon source (Rippka and Herdman, 1992). In addition to its symbiotic and heterotrophic competence, N. punctiforme is amenable genetic analysis and replicates, or recombines into its chromosome, exogenous DNA following electroporation or conjugation with Escherichia coli as a donor. Cells can be mutagenized by chemical agents, exogenously supplied transposons, or by targeted gene replacement and the mutant phenotypes complemented by the wild-type gene replicated in trans in a shuttle plasmid (Cohen et al., 1998). The N. punctiforme genome, at approximately 7.54 Mb with a 45.2 mol % GC, is amongst the largest of all cyanobacteria (Rippka and Herdman, 1992), is significantly larger than any other cyanobacterium that has been sequenced and is the largest microbial genome sequenced thus far by the JGI. Sequence analysis of N. punctiforme is likely to yield unique information on global regulation of multiple developmental pathways, symbiotic association, regulation of carbon and nitrogen fixation, and phylogenetic relations amongst the cyanobacteria, the most ancient lineage of oxygen-producing photosynthetic organisms on earth.

References:

Castenholz, R.W. and J.B. Waterbury. 1989. Oxygenic photosynthetic bacteria. Group I. Cyanobacteria. In: Bergey’s Manual of Systematic Bacteriology, vol. 3, pp. 1710-1789, J.T. Staley, M.P. Bryant, N. Pfenning and J.G. Holt (eds.), Williams and Wilkins, Baltimore.

Cohen, M.F., J.C. Meeks, Y.A. Cai and C.P. Wolk. 1998. Transposon mutagenesis of heterocyst-forming filamentous cyanobacteria. Methods Enzymol. 297:1-17.

Dodds, W.K., D.A. Gudder and D. Mollenhauer. 1995. The ecology of Nostoc. J. Phycol. 31:2-18.

Meeks, J.C. 1998. Symbiosis between nitrogen-fixing cyanobacteria and plants. BioScience 48:266-276.

Potts, M. 2000. Nostoc. In: The Ecology of Cyanobacteria: Their Success in Time and Space. Kluwer Academic Publishers, in press.

Rippka, R. and M. Herdman. 1992. Pasteur Culture Collection of Cyanobacterial Strains in Axenic Culture, Catalogue and Taxonomic Handbook. 103 pp. Institut Pasteur, Paris.

Nostoc punctiforme (Munich University)
Nostoc punctiforme is the microsymbiont of the unique fungal endocyanosis Geosiphon pyriforme. During the establishment of this endosymbiosis fungal hyphae incorporate a specific stage of the N. punctiforme life cycle, formed during the differentiation from the motile hormogonium to the immotile primordium stage.