Cyanobacteria
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Cool Facts About Cyanobacteria!
We have cyanobacteria to thank for the oldest known fossils on the planet! Stromatolites are the mineralized remnants of layers of cyanobacterial mats, and some are well over 3 billion years old (Eisenberg & Chapman, 2021).
This ancient lineage has managed to colonize essentially every type of habitat on Earth: they are found in lakes and rivers, in oceans and estuaries, on tropical plants and arid desert soils, and just about everywhere else scientists have looked.
Heads up: you can also visit our guide to freshwater cyanobacteria of New Jersey to read comprehensive descriptions of the cyanobacteria commonly observed by NJCWST and see more images of each genus!
Morphology of Cyanobacteria
As one might expect from such an ecologically diverse group of organisms, cyanobacteria vary dramatically in their morphology: some types exist as nondescript, solitary cells, while others take on complex forms composed of multiple specialized cell types. Identification guides often separate cyanobacteria into two broad groups: coccoid and filamentous. This distinction is based only on morphology, and does not reflect the evolutionary relationships between different taxa—it just makes the identification process a little easier!
Coccoid cyanobacteria
Coccoid cyanobacteria are, in the broadest sense, basically just simple cells with a generally rounded shape. The cells of most coccoid cyanobacteria are spherical, oblong, or rod-shaped, but other shapes are possible as well—some cells are heart-shaped or hemispherical following cell division, for example.
Many coccoid cyanobacteria form colonies of cells held together by mucilage. This is a viscous, gelatinous substance produced by the cells, and it can hold colonies together in different ways. In some colonies, the cells are all uniformly surrounded by a common colonial mucilage; in others, cells are tethered together by a system of mucilaginous stalks or strands, bearing the cells at their ends. Sometimes, smaller groups of cells or individual cells are also surrounded by their own distinct mucilaginous envelopes, in addition to the colonial mucilage. Colony shapes include spherical, sheet-like, and irregular, among other forms. Some colonies contain only a few cells, while others contain hundreds to thousands. There are also coccoid cyanobacteria that exist primarily as solitary cells, or in irregular aggregates of cells (not forming) distinct colonies.
Coccoid cyanobacteria observed by NJCWST include: Aphanocapsa, Merismopedia, Microcystis, Snowella, Woronichinia
Solitary coccoid cyanobacteria
Solitary coccoid cyanobacteria occur as single cells or as pairs of cells (following cell division). Though these cells may aggregate into irregular groups or agglomerations, they do not form distinct colonies.
Solitary coccoid genera observed by NJCWST include: Synechococcus.
Filamentous cyanobacteria
Filamentous cyanobacteria form chains of cells that are connected end-to-end. The width, length, and general appearance of these filaments varies widely: they can be perfectly straight or corkscrew-like coiled, branched or un-branched, and they may be solitary or gathered into masses of many filaments. Individual cells within the filaments are commonly barrel-shaped, cylindrical, or disc-shaped. In some taxa, all the cells in a filament are of uniform size, shape, and function. In other taxa, the cells take on different appearances and/or physiological roles within the filament. For instance, some filaments are heteropolar, meaning the two ends do not look the same—for instance, one end may be widened, while the other is tapered to a narrow point. In these cases, the cells at one end often have a different size and shape from those at the other end.
Some types of filamentous cyanobacteria are capable of forming heterocytes and akinetes, which are specialized cell types. Heterocytes contain an enzyme called nitrogenase, which converts atmospheric molecular nitrogen into ammonia. Akinetes are thick-walled resting (non-dividing) cells capable of surviving harsh environmental conditions; they possess an accumulation of the chemical compounds necessary for new growth once environmental conditions improve. Though many of the heterocyte-forming taxa also form akinetes, this is not always the case. Heterocytes and akinetes differ from vegetative cells morphologically. Heterocytes may take on spherical, cylindrical, pointed or conical, or flattened shapes, and are usually not much wider than vegetative cells, but may be of a different length. Heterocytes’ cell content is pale and homogeneous, and is commonly yellowish or yellow-green in color. Akinetes commonly have a cylindrical or oval shape, though they can also be spherical, and they can be much larger than the vegetative cells. Akinetes’ cell content often has a granular appearance, and the outer layer of the cell wall may be widened, textured, and/or yellowish to orange-brownish in color.
Heterocytous (heterocyte-forming) filamentous genera observed by NJCWST include: Aphanizomenon, Cuspidothrix, Dolichospermum, Nostoc, Raphidiopsis, Tolypothrix.
Aheterocytous (non-heterocyte-forming) filamentous genera observed by NJCWST include: Jaaginema, Limnoraphis, Planktolyngbya, Planktothrix, Pseudanabaena.
Ecology of Cyanobacteria
As we mentioned earlier, cyanobacteria really do thrive in all kinds of habitats! Recently, however, certain genera commonly found in the plankton of lakes and reservoirs have attracted attention from scientists, news media, and the general public. The publicity hasn’t exactly been good: these taxa are sometimes responsible for unsightly—and sometimes toxic—harmful algal blooms (HABs). These genera typically possess clusters of gas vesicles, called aerotopes, which make the cells buoyant.
Common bloom-forming genera include Microcystis, Dolichospermum, Limnoraphis, Woronichinia, and Aphanizomenon.
Microcystis
Limnoraphis (filamentous) and Woronichinia (colonial), in a water sample taken from an algal bloom.
A full list of the cyanobacterial genera observed by NJCWST and images of each genus can be found at NJCWST's Freshwater Cyanobacteria of New Jersey website:
References
Eisenberg, L., & Chapman, J. (2021, March 1). Giant Stromatolites of Capitol Reef State Park. National Park Service. https://www.nps.gov/articles/stromatolites-of-capitol-reef-national-park.htm
Johansen, J. R., & Komárek, J. (2015). Coccoid Cyanobacteria. In J. D. Wehr, R. G. Sheath, & J. P. Kociolek (Eds.), Freshwater Algae of North America: Ecology and Classification (2nd ed., pp. xyz). Waltham, MA: Elsevier.