Background information
Toxic cyanobacteria
Cyanobacteria [1] are a natural part of the biological communities in water bodies. Some cyanobacteria float freely in the water column (planktic), while others colonize surfaces like stones or the bottom of the water body (benthic). At high nutrient concentrations (esp. phosphorus), populations of cyanobacteria may develop massively.
Beside chlorophyll, cyanobacteria contain accessory photopigments, principally the blue phycocyanin and the red phycoerythrin. These pigment combinations cause the different colourings of cyanobacteria which lead to discoloration of the water when cyanobacteria proliferate massively. However, only decaying cyanobacterial blooms appear “truly blue” due to the release of the water-soluble blue phycocyanin from the damaged cells.
Many species of cyanobacteria may produce toxins which can lead to intoxications in animals and humans. Especially abundant freshwater cyanobacteria like Microcystis, Planktothrix, Aphanizomenon and Anabaena may be toxic and, moreover, develop massively (“blooms”) under suitable conditions, eventually outcompeting all other phytoplankton. To assess whether cyanobacteria pose a threat to a drinking water supply or bathing water, it is crucial to identify potentially toxic cyanobacteria quickly and reliably.
A detailed identification of cyanobacteria at species level is not only difficult, but often not necessary; mostly, the identification to genus level is sufficient and can be performed by staff after some training.
In the following you will find an overview of the most frequently encountered cyanobacteria which can produce toxins. More information about cyanobacteria can be found in the literature, as well as photos or taxonomic information and references in the internet.
With these sources – and eventually also with additional limnological expertise – you will be able to identify the most important cyanobacteria in your water body and establish a list for their identification in the future.
Abundant toxic cyanobacteria
The following cyanobacteria often develop massively and may produce toxins.
Microcystis
The genus Microcystis occurs in freshwaters worldwide. Its cells are spherical to ovoid with a diameter between 2.5 – 8 µm and are aggregated in colonies, which are often easily visible to the naked eye. The cells contain gas vesicles enabling the colonies to float and form streaks or even thick scums at the water surface. Microcystis species are differentiated mainly by their cell size and shape of the colony.
The most frequent Microcystis species in eu- to hypertrophic water bodies are M. aeruginosa , M. flos-aquae, M. viridis , M. ichthyoblabe and M. wesenbergii . They were found to produce microcystins, but the production of other toxins such as anatoxins or cylindrospermopsins has not been encountered. At high nutrient concentrations Microcystis often tends to mass developments. In such “blooms” microcystins can easily reach concentrations which are hazardous to health when higher amounts of water are swallowed.
Detailed information about the taxonomic identification of Microcystis species can be found here.
Planktothrix
Cyanobacteria of the genus Planktothrix grow as long filaments [2] with gas vesicles. The cells are usually broader than long with diameters of about 3.5 – 10 µm. The filaments may be motile and may pass through filters during drinking water treatment.
Microcystins are the toxins most frequently found in Planktothrix. Anatoxin-a and saxitoxins have been detected only occasionally. The most abundant microcystin-producers of this genus are Planktothrix agardhii and Planktothrix rubescens. The two species are distributed worldwide, but inhabit different ecological niches:
Planktothrix agardhii often dominates the plankton in eu – to hypertrophic, shallow and thus frequently mixed water bodies. The mixing of the water column causes Planktothrix agardhii to be more or less homogenously distributed within the water column without forming scums, as observed for several other cyanobacteria.
In contrast, Planktothrix rubescens inhabits deep, stratified, meso- to eutrophic lakes where it occurs in the metalimnion [5] during summer as its pigment composition permits growth in the lower light conditions at this depth while simultaneously benefitting from higher nutrient availability in the deeper waters. It is usually only during the autumnal turnover that this species is entrained throughout the whole water column and when it may also form surface blooms under high nutrient conditions. However, in some water bodies Planktothrix rubescens appears year-round, even under ice.
Detailed information about the taxonomic identification of Planktothrix species can be found here.
Aphanizomenon/Cuspidothrix
Representatives of the genus Aphanizomenon grow as filaments with 20 – 50 cells per filament [2] and a species-specific cell diameter between 3 – 7 µm. In addition, heterocysts [3] and akinetes [4] may appear in the filaments.
In Aphanizomenon flos-aqaue the single filaments aggregate to bundles floating in the water which may also form surface scums. The colonies look like grass cuttings or larch needles and are easily to recognize. Other species appear only as solitary filaments including Aphanizomenon gracile and Cuspidothrix (formerly Aphanizomenon) issatschenkoi. Most species of Aphanizomenon are planktic freshwater inhabitants, although Aphanizomenon spp. also may form blooms in the Baltic Sea.
Cylindrospermopsin, PSP (saxitoxins) and anatoxin-a have been found in Aphanizomenon spp., microcystins have not been found so far. The species most often associated with or confirmed for toxin-production are Aphanizomenon gracile, Cuspidothrix (formerly Aphanizomenon) issatschenkoi, Aphanizomenon flos-aquae and Aphanizomenon ovalisporum.
Detailed information about the taxonomic identification of Aphanizomenon species can be found here.
Anabaena (syn. Dolichospermum)
Anabaena species grow as filaments [2], in which heterocysts [3] and akinetes [4] may appear. The cells (4-14 µm) are spherical to cylindrical with more or less deep constrictions at cross walls. The filaments may be straight (e.g. Anabaena planctonica), coiled (e.g. A. spiroides) or wound to form larger colonies (e.g. A. lemmermannii). The genus Anabaena is distributed globally in freshwaters, but some species also occur in brackish waters. Also benthic species exist forming mats on different substrates (e.g. stones).
Examples of all of the known classes of cyanotoxins have been found in species of the genus Anabaena: microcystins, cylindrospermopsin, anatoxin-a, anatoxin-a (s) as well as PSP (saxitoxins). Besides in surface scums, high toxin concentrations may also occur in mats.
Detailed information about the taxonomic identification of Anabaena species can be found here.
Nodularia
Members of the genus Nodularia mainly occur in brackish waters. The (so far) only toxic species Nodularia spumigena grows in filaments [2] which may be more or less straight, curved or irregularly coiled. Heterocysts [3] are regularly distributed within the filaments. N. spumigena occurs globally in brackish and slightly salty waters. In the Baltic Sea N. spumigena regularly forms mass developments in summer and forms scums during calm weather conditions due to floating filaments.
N. spumigena may produce the hepatotoxic nodularins.
Detailed information about the taxonomic identification of Nodularia species can be found here.
Cylindrospermopsis
The genus Cylindrospermopsis occurs primarily in subtropical/tropical water bodies. However, the range of the potentially toxic Cylindrospermopsis raciborskii appears to have extended further into temperate zones during recent decades. C. raciborskii forms filaments [2] which may be straight, coiled or spiral. The heterocyst [3] is conical or lancet-like and situated at the end of the filament.
C. raciborskii may produce cylindrospermopsins and PSP (saxitoxins).
Detailed information about the taxonomic identification of Cylindrospermopsis species can be found here.
Other toxin-producing cyanobacteria
The following cyanobacteria may also produce toxins. However, the health hazards to drinking water production and bathing are globally regarded to be less relevant as mass developments of these genera appear to be less common. An exception is the genus Lyngbya occurring often massively in (sub)tropical environments where it can cause severe dermatitis (“seaweed dermatitis” or “swimmers’ itch”).
Anabaenopsis
The genus Anabaenopsis comprises around 15 filamentous species. The filaments [2] are straight, curved or coiled with heterocysts [3] and akinetes [4]. As filaments often break after formation of heterocysts, these then appear at the terminal end of the filament.
In some species of the genus Anabaenopsis microcystins have been detected sporadically.
Detailed information about the taxonomic identification of Anabaenopsis species can be found here.
Cylindrospermum
Members of the genus Cylindrospermum grow as more or less curved filaments [2] which aggregate to loose or dense mats on surfaces in less eutrophic water bodies. Cells are mostly cylindrical, and heterocysts [3] only develop at the terminal end of the filament and are oval, ovoid or conical in shape. Akinetes [4] only develop in the vicinity of heterocysts.
Anatoxin-a has been detected in the genus Cylindrospermum sporadically.
Detailed information about the taxonomic identification of Cylindrospermum species can be found here.
Lyngbya
Representatives of the genus Lyngbya form thick filaments [2] which often aggregate to solid mats. The cells are always broader than high, no heterocysts [3] or akinetes [4] exist. Lyngbya is distributed globally, mainly in brackish and marine environments.
Some species of the genus Lyngbya have been found to produce lyngbyatoxins, aplysiatoxins, cylindrospermopsins and PSP (saxitoxins).
Detailed information about the taxonomic identification of Lyngbya species can be found here.
Nostox
Cyanobacteria belonging to the genus Nostoc form long filaments [2] with cylindrical, barrel-shaped to almost spherical cells, in which heterocysts [3] and akinetes [4] may occur. Filaments are often aggregated to amorphous or spherical, gelatinous colonies.
Some species of the genus Nostoc including lichen symbionts have been found to produce microcystins and nodularins.
Detailed information about the taxonomic identification of Nostoc species can be found here.
Oscillatoria
The genus Oscillatoria forms long, unbranched filaments [2] with cells always broader than long. Heterocysts [3] and akinetes [4] do not exist. Both planktic and benthic species occur in freshwater, brackish and marine habitats.
Some species of Oscillatoria have been found to produce microcystins, anatoxin-a, homoanatoxin, and aplysiatoxin.
Detailed information about the taxonomic identification of Oscillatoria species can be found here.
Phormidium
Members of the genus Phormidium grow as filaments [2] which are aggregated in mats on different substrates (e.g. soil, water plants, stones etc.). Heterocysts [3] and akinetes [4] do not exist.
Anatoxin-a and homoanatoxin-a have been detected in some Phormidium species. Microcystins have been found only sporadically.
Detailed information about the taxonomic identification of Phormidium species can be found here.
Raphidiopsis
Representatives of the genus Raphidiopsis grow as straight, waved or screw-like coiled filaments [2] usually slightly attenuated towards both ends. Akinete [4] formation has been observed, but no heterocysts [4] are differentiated. Only a few planktic freshwater species exist.
In Raphidiopsis cylindrospermopsin, anatoxin-a, homoanatoxin-a, and PSP (saxitoxins) have been found. The species most often associated with or confirmed for toxin-production are R. mediterranea, R. curvata and R. brookii.
Detailed information about the taxonomic identification of Raphidiopsis species can be found here.
Schizothrix
Cyanobacteria belonging to the genus Schizothrix form filaments [2] usually slightly attenuated toward both ends and surrounded by gelatinous sheaths. The cells are cylindrical, slightly conical towards the end of the filament. Heterocysts [3] and akinetes [4] do not exist.
The filaments usually occur as built up layers, e.g. on stones, and may be thus visible with the naked eye. The layers may differ in appearance and can be encrusted by calcium carbonate.
Some species have been found to produce aplysiatoxin.
Detailed information about the taxonomic identification of Schizothrix species can be found “here“http://www.algaebase.org/search/genus/detail/?genus_id=43075.
Tychonema
Representatives of the genus Tychonema are typically straight with a cell diameter between 5 – 16 µm. The filaments are isodiametric with a rounded apical cell. The cells may have widended thylakoids resembling “vacuoles” and the centripetal formation of the cross walls can often be deteced. Heterocysts [3] and akinetes [4] do not exist. The different species described mainly differ in the cell diameter and the habitat in which they preferably occur (planktic, benthich, tychoplanktic, epiphytic).
The production of anatoxin-a is verified for T. bornetii and T. bourrellyi, and very likely for T. tenue.
Detailed information about the taxonomic identification of Tychonema species can be found here.
