Table of Contents:

Production

Producing Cyanobacteria

Qualitative and quantitative information on microcystin production in particular cyanobacterial species has been gathered through analyses of quasi- monospecific bloom material and, more importantly, large numbers of individual strains isolated from freshwater samples. More recent studies employ sensitive molecular and chemical tools such as PCR, mass spectrometry or ELISA to determine toxins or genes related to their production directly in colonies or filaments picked from water samples. This helps to avoid bias due to eventually selective isolation procedures and allows more detailed studies on the ecology of toxin-producing cyanobacteria. Furthermore, molecular tools are applied to clarify the taxonomic status of toxin-producing cyanobacteria and to complement the identification of toxin producers by verifying the presence of genes encoding toxin biosynthesis (see section 13.6).

Microcystin-producing strains can be found in all higher-level taxa of cyanobacteria, that is, in species belonging to the orders Chroococcales, Oscillatoriales, Nostocales, and Stigonematales; data for the order Pleuro- capsales, however, are scarce. Within the orders, the distribution of micro- cystin occurrence at the level of genera or species is patchy and does not show consistency. Firstly, not all genera of an order produce microcystins; for example in the order Nostocales, microcystins are produced by members of the genera Dolichospermum (Anabaena) and Nostoc, but have never been confirmed for the closely related genus Apbanizomenon. Secondly, any particular genus or species may contain both producing (toxigenic) and nonproducing strains. At the time of the publication of this book, microcystin-producing (and nonproducing) strains are known primarily from freshwater species of Microcystis, Planktothrix, Dolichospermum, and Nostoc (Sivonen & Jones, 1999; Oksanen et al., 2004; Mowe et al., 2015; Flarke et ah, 2016; Bernard et ah, 2017; Buratti et ah, 2017; Table 2.2). Very rarely, microcystins have been reported in single strains from other genera, including Anabaenopsis, Arthrospira, Fischerella, Pseudanabaena, Pbormidium, Synechococcus and Radiocystis (Ballot et ah, 2005; Carmichael & Li, 2006; Lombardo et ah, 2006; Izaguirre et ah, 2007; Nguyen et ah, 2007; Mohamed 8c Al Shehri, 2009; Cires et ah, 2014; Table 2.2).

Most of these cyanobacteria are of planktonic nature and some of them, like Microcystis, are known for their ability to form surface blooms under favourable conditions (see Chapter 4). Microcystins have also been detected in halophilic Synechococcus and Dolichospermum (Anabaena) from the Baltic Sea (Carmichael & Li, 2006; Flalinen et ah, 2007).

Microcystin-producing strains of the genera listed above are distributed globally and can be found in tropical, temperate and polar habitats (Hitzfeld et ah, 2000; Mowe et ah, 2015; Harke et ah, 2016) as well as in extreme habitats such as hot springs and hypersaline lakes (Carmichael &C Li, 2006; Kotut et ah, 2006). Microcystins have also been detected in a symbiotic strain of Nostoc in a lichen (Oksanen et ah, 2004) and in a soil isolate of Haphalosiphon hibernicus (Prinsep et ah, 1992).

Nodularins have so far been found largely in strains of the genus Nodularia, primarily in Nodularia spumigena. Toxigenic strains of Nodularia spumi- gena have been reported from the Baltic Sea, brackish water estuaries and coastal freshwater lakes of Australia, South Africa, New Zealand and Turkey (Bolch et ah, 1999; Ak^aalan et ah, 2009). As with microcystins, both nod- ularin-producing and nonproducing strains exist in this species (Lehtimaki et ah, 1994; Bolch et ah, 1999). In addition, single findings of nodularin in Nodularia sphaerocarpa from a hot spring, in a symbiotic Nostoc, and

Table 2.2 Cyanobacterial taxa potentially producing microcystins and nodularins

Toxin

Taxon

Habitat

Microcystin

Microcystis sp.

Planktonic

Dolichospermum (Anabaena) sp.

Planktonic

Planktothrix agardhii

Planktonic

Planktothrix rubescens

Planktonic

Radiocystis sp.

Planktonic

Arthrospira sp.

Planktonic

Anabaenopsis sp.

Planktonic

Calothrix sp.

Planktonic

Oscillatoria sp.

Planktonic

Fischerella sp.

Planktonic, benthic

Annamia toxica

Planktonic

Synechococcus sp.

Planktonic

Pseudanabaena sp.

Planktonic

Phormidium sp.

Planktonic

Anabaena sp.

Benthic

Nostoc sp.

Planktonic, benthic, symbiotic (lichen)

Aphanocapsa sp.

Planktonic

Plectonema sp.

Benthic

Leptolyngbya sp.

Symbiotic (coral), periphytic

Merismopedia sp.

Periphytic

Haphalosiphon hibernicus

Terrestrial

Nodularin

Nodularia spumigena

Planktonic

Nodularia sp.

Benthic

Nostoc sp.

Symbiotic (lichen)

Iningainema pulvinus

Benthic

Only cyanobacteria are listed for which toxin production was verified in cultured strains by NMR, mass spectrometry or by combinations of HPLC-PDA, ELISA, toxicity testing and/or molecular detection of mcy genes. References earlier than 1999 are summarised in Sivonen & Jones (1999). In bold are taxa that are known to frequently produce microcystins and that can form blooms.

in the benthic Iningainema pulvinus (Nostocales) from Australia have been reported (Beattie et ah, 2000; Gehringer et ah, 2012; McGregor & Sendall, 2017). Occasionally, nodularin has been detected in pelagic and benthic freshwater ecosystems in which none of the known nodularin producers could be identified, indicating that further species may be identified as nodularin producers in future (Graham et ah, 2010; Wood et ah, 2012; Beversdorf et ah, 2017).

 
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