Summary 3

Nostoc is a cyanobacteria genus that is occasionally found in freshwater phytoplankton assemblages, but is not usually associated with toxic planktonic blooms. Nostoc is more commonly associated with benthic environments, where is can form form mats of dark, rubbery, irregular or egg-shaped colonies on damp soils or mixed in with shoreline vegetation of lakes and ponds. Some species of Nostoc are highly resistant to drought and heat, and may be successfully rehydrated from dried soil crusts surrounding dry lakes.

Description 4

IndividualNostoc cells are spherical, oval, or barrel-shaped, and tiny (3.5-8 μm; for comparison, a strand of spider silk is about 5 μm wide). The cells are joined together end-to-end to form long, unbranched filaments, closely resembling Anabaena and Dolichospermum, filaments. But Nostoc filaments are surrounded by a distinctive, firm, often rubbery mucilage and form spherical, egg-shaped, or irregular colonies.

A few Nostoc species form small planktonic colonies (<1 μm diameter). The mucilage surrounding these planktonic colonies may be transparent, or stained brownish orange by organic compounds in the water. Most Nostoc species form macroscopic colonies; these colonies range in color from bright blue-green to almost black. The macroscopic colonies can produce tiny, microscopic colony buds that separate from the mother colony and become planktonic.

In addition to ordinary (vegetative) cells, the filaments may contain heterocytes (also called heterocysts) and large, granular, thick-walled akinetes. Heterocytes are specialized cells that convert dissolved nitrogen gas into ammonium that can be used for cell growth. Akinetes are resting cells that are resistant to cold temperatures and other unfavorable environmental conditions, and can overwinter in lake sediments. Akinete are rarely observed in Nostoc filaments.

Some Nostic species form gas vesicles, which give the cell a mottled appearance.

Ecology 4

Nostoc is not a usually found in planktonic cyanobacteria blooms, despite the ability of some species to form gas vesicles.

  • The gas vesicles in Nostoc cells provide a mechanism to move up and down in the water column, which increases access to nutrients and other growth factors.

Freshwater species of Nostoc are usually found in shallow water associated with shoreline vegetation in low-nutrient (oligotrophic or mesotrophic) lakes and ponds, especially water that is slightly acidic, boggy, or peaty.

Nostoc is capable of fixing dissolved nitrogen gas, which helps provide nitrogen in boggy sites where inorganic nitrogen (ammonium, nitrate, and nitrite) is limiting to other types of algae.

Several species are consumed by humans, notably Nostoc flagelliforme and Nostoc sphaeroides

  • Nostoc flagelliforme has been found to contain BMAA (see toxicity discussion)

Toxicity 4

Identifying which cyanobacteria species are producing toxins is more difficult that it sounds. Historically, cyanobacteria taxa were described as "potentially" toxic based on whether they were collected in a toxic bloom. With the advancement of culturing techniques and genetic analysis, toxicity information is becoming more exact. But this is an ongoing process, so the toxicity information on these pages should be considered a work in progress.

Nostoc cells may produce microcystins (liver toxin), lipopolysaccharides (skin irritants), and BMAA (beta-Methylamino-L-alanine; nerve toxin). These toxins are released into the ambient environment when the cell wall is disrupted (cell lysis).

  • Microcystins are rapidly degraded by naturally occurring but specialized bacteria.
  • If the specialized bacteria are not present, microcystins can persist in the aquatic environment for months.
  • BMAA can bioaccumulate in zooplankton and fish, so this nerve toxin can contribute to health risks long after the toxic bloom has died back.

Not all Nostoc blooms result in the release of toxins.

Similar Genera 4

Information Sources 4

  • Bennett, L. 2017. Algae, cyanobacteria blooms, and climate change. Climate Institute Report, April 2017.
  • Berg, M and M. Sutula. 2015. Factors affecting the growth of cyanobacteria with special emphasis on the Sacramento-Jan Joaquin Delta. Southern California Coastal Water Research Project Technical Report 869.
  • Caldwell Eldridge, S., R. Wood, and K. Echols. 2012. Spatial and temporal dynamics of cyanotoxins and their relation to other water quality variables in Upper Klamath Lake, Oregon, 2007-09. USGS Scientific Investigations Report 2012-5069.
  • Chorus, I. and J. Bartram (Eds). 1999. Toxic cyanobacteria in water: a guide to their public health consequences, monitoring and management. The World Health Organization E & FN Spon, London.
  • EPA. 2014. Cyanobacteria and Cyanotoxins: Information for Drinking Water Systems. U. S. Environmental Protection Agency, Office of Water, EPA-810F11001.
  • Graham, L. E., J. M. Graham, L. W. Wilcox, and M. E. Cook. 2016. Algae, Third Ed., ver 3.3.1 . LJLM Press,
  • Granéli, E. and J. T. Turner (Eds.) 2006. Ecology of Harmful Algae. Ecological Studies, Vol. 189, Springer.
  • Komárek, J. 2013. Cyanoprokaryota, Part 3: Heterocystous Genera. Süßwasserflora von Mitteleuropa, Vol. 19/3, B. Büdel, G. Gärtner, L. Krienitz, M. Schagerl (Eds). Springer Spektrum, Heidelberg, GE.
  • Lage, S., H. Annadotter, U. Rasmussen, and S. Rydberg. 2015. Biotransfer of B-N-Methlamino-L-alanine (BMAA) in a eutrophicated freshwater lake. Marine Drugs 13:1185-1201.
  • Matthews, Robin A., "Freshwater Algae in Northwest Washington, Volume I, Cyanobacteria" (2016). A Collection of Open Access Books and Monographs. 6. (also see:
  • Meriluoto, J., L. Spoof, and G. Codd. 2017. Handbook of Cyanobacterial Monitoring and Cyanotoxin Analysis. John Wiley & Sons, Chichester, UK.
  • Paerl, H. W. 2014. Mitigating harmful cyanobacterial blooms in a human- and climatically-impacted world. Life 2014 4:988-1012.
  • Roney, B. R., L. Renhui, S. A. Banack, S. Murch, R. Honegger, and P. A. Cox. 2009. Consumption of {\em fa cai Nostoc} soup: a potential for BMAA exposure from Nostoc cyanobacteria in China? J. Amyotrophic Lateral Sclerosis, 10: 44-49
  • Walsby, A. E. 1994. Gas vesicles. Microbiological Reviews 58:94-144
  • Synonyms 4

    Nostoc has no commonly used synonyms.

    About 5

    This guide was prepared by Dr. Robin Matthews, former Director of the Institute for Watershed Studies ( and professor emeritus at Western Washington University. In addition to this guide she has also written two ebooks (more on the way) on phytoplankton identification (see the "algae books" link on and an online key to the cyanobacteria (

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