Summary 2

Microcystis is a cyanobacteria genus that is commonly found in freshwater phytoplankton assemblages. In nutrient-rich lakes it can form dense blooms. There are several common species of Microcystis that may be present simultaneously in a bloom. The most common species, Microcystis aeruginosa, is often found in toxic cyanobacteria blooms.

Description 3

Individual Microcystis cells are spherical or oval, and tiny (2.5-5 μm, or about the width of a strand of spider silk). Under magnification they may appear granular or mottled and dark brown due to the presence of gas vesicles in the cells. The cells are surrounded by clear, often transparent mucilage, forming dense, spherical or irregular colonies.

Ecology 3

Microcystis blooms often form during warm, calm weather in lakes and ponds with relatively high nutrient concentrations (nitrogen or phosphorus) or low nitrogen to phosphorus ratios (N:P<15).

  • Recent work suggests that high total phosphorus (TP) or total nitrogen (TN) concentrations are better predictors of bloom formation than N:P ratios.
  • Microcystis does not fix atmospheric nitrogen, but is very efficient in taking up ammonium and urea, and often forms blooms when nitrogen concentrations are limiting to other algae.
  • Microcystis blooms may follow blooms of nitrogen-fixing Aphanizomenon .
  • Microcystis can use low concentrations of the herbicide glyphosate as a phosphorus source.

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

Microcystis blooms usually contain other types of Cyanobacteria, especially Aphanizomenon , Dolichospermum (aka Anabaena), Gloeotrichia, and Woronichinia Microcystis colonies may be surrounded by short filaments of Pseudanabaena (potentially toxic Cyanobacteria) and inactive Chlamydomonas cells (motile green algae).+

Toxicity 3

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.

Microcystis cells may produce anatoxins (nerve toxin), 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).

  • The toxin microcystin was first isolated from Microcystis aeruginosa.
  • 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.
  • Anatoxins are rapidly degraded by sunlight and at pH levels that are slightly above neutral (neutral pH = 7.0). At low pH levels, and in the absence of light, anatoxins may persist in the aquatic environment for a few weeks.
  • BMAA can bioaccumulate in zooplankton and fish, so this nerve toxin can contribute to health risks long after the toxic bloom has died back.

Higher water temperatures and light appear to be associated with increased toxin production.

Not all Microcystis blooms result in the release of toxins.

Similar Genera 3

  • Cyanobacteria: Aphanocapsa, Aphanothece, Snowella, Pannus, Woronichinia
  • Green Algae: Sphaerocystis, Tetraspora
  • Other: Sphaeroeca, Sulfur bacteria

Information Sources 3

  • 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.
  • D'Anglada, L., J. Donohue, J. Strong, and B. Hawkins. 2015. Health effects support document for the cyanobacterial toxin anatoxin-A. U.S. Environmental Protection Agency, Office of Water, EAP-820R15104, June 2015.
  • 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, ww.ljlmpress.com.
  • Granéli, E. and J. T. Turner (Eds.) 2006. Ecology of Harmful Algae. Ecological Studies, Vol. 189, Springer.
  • 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. http://cedar.wwu.edu/cedarbooks/6 (also see: http://www.wwu.edu/iws/).
  • Maršálek, B., L. Bláha, and P. Babica. 2003. Analyses of microcystins in the biomass of Pseudanabaena limnetica collected in Znojmo Reservoir. Czech Phycology, Olomouc, 3:195-197.
  • 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.
  • Qui, H., J. Geng, H. Ren, X. Xia, X. Wang, and Y. Yu. 2013. Physiological and biochemical responses of Microcystis aeruginosa to glyphosate and its Roundup® formulation. J. Hazardous Materials, 248-249:172-176.
  • Walsby, A. E. 1994. Gas vesicles. Microbiological Reviews 58:94-144

Synonyms 4

Microcystis has no commonly used synonyms.

About 5

This guide was prepared by Dr. Robin Matthews, former Director of the Institute for Watershed Studies (http://www.wwu.edu/iws/) 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 http://www.wwu.edu/iws/) and an online key to the cyanobacteria (http://www.snoringcat.net/cyanobacteria_key/index.html).

Sources and Credits

  1. (c) rmatth, some rights reserved (CC BY-NC-SA), uploaded by rmatth
  2. (c) rmatth, some rights reserved (CC BY-NC-SA)
  3. Adapted by rmatth from a work by (c) Bryan Milstead, some rights reserved (CC BY-SA)
  4. (c) rmatth, some rights reserved (CC BY-NC)
  5. Adapted by rmatth from a work by (c) Bryan Milstead, some rights reserved (CC BY-NC-SA)

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