Raphidiopsis mediterranea

Homoanatoxin-a, obtained from various freshwater cyanobacteria, is a relatively rare natural analog of anatoxin-a for which the C-11 side chain is extended by one methylene unit (Figure 6.4). It was originally isolated from Planktothrix sp. (formerly Oscillatoria) in 1992 [51]. It has recently been isolated from Raphidiopsis mediterranea Skuja from Japan [52] and Planktothrix (formerly Oscillatoria) formosa blooms in Ireland [53]. 

Biosynthesis of homoanatoxin-a was examined using Oscillatoria formosa and a mechanism similar to that for anatoxin-a was proposed [13,14]. The origin of the C-12 methyl group that distinguishes homoanatoxin-a from anatoxin-a, was shown through feeding experiments performed with L-[methyl- C]-methionine in the culture of Raphidiopsis mediterranea Skuja. It was proposed that the S-methyl of methionine is transferred to the toxin via S-adenosyl-L-methionine (SAM)-mediated methylation [55]. 

In Japan, the first detection of AN and its degradation product, epoxy-AN, have been reported (Park et al. 1993). This was also the first study to show that Microcystis could produce both AN and microcystins. The predominant species were Anabanea and Planktothrix with toxin concentrations in the range 0.4-16 pg AN/g. In addition, AN, HMAN, and a new compound, hydroxy-HMAN, were isolated from Raphidiopsis mediterranea in Japan (Namikoshi et al. 2003 Watanabe et al. 2003). AN was also found in four of 26 samples from Korean lakes, collected during 1992-1995 (Park etal. 1998). 

Namikoshi, M., Murakami, T, Fujiwara, T, Nagai, H., Niki, T., Harigaya, E., Watanabe, M. E, Oda, T, Yamada, I, and Tsu-jimura, S. 2004. Biosynthesis and transformation of homoanatoxin-a in the cyanobacterium Raphidiopsis mediterranea Skuja and structures of three new homologues. Chem Res Toxicol 17,1692-1696. 

Watanabe, M.F., Tsujimura, S., Oishi, S., Niki, T, and Namikoshi, M. 2003. Isolation and identification of homoanatoxin-a from a toxic strain of the cyanobacterium Raphidiopsis mediterranea Skuja isolated from Lake Biwa, Japan. 42. Phycologia 42, 364-369. 

In Einland, Sivonen et al. (1990) performed the first survey of cyanobacterial blooms in 1985-1987 and found that 13 out of 30 bloom samples contained AN. A number of cattle poisonings associated with Anabanea blooms occurred (Sivonen et al., 1990). The first identification of HMAN was isolated from a strain of Planktothrix formosa (Skulberg et al., 1992). AN was also implicated as the causative agent in incidents of fatal canine neurotoxicosis in Ireland (James et al., 1997) and Erance (Gugger et al., 2005). AN and HMAN were found in Anabaena and benthic Planktothrix spp. (Eurey et al., 2003a). AN and HMAN have also been reported in Japan and were isolated from Raphidiopsis mediterranea (Namikoshi et al., 2003). 

Anatoxin A is the fast-acting and highly effective poison of the cyanobacterium Anabaenaflos-aquae, which is ubiquitous in freshwater. Anatoxin A, also known as Very Fast Death Factor , was isolated from Anabaenaflos-aquae in 1977 by Paul Gorham at the National Research CoimcU in Ottawa. [553,554] The structure had already been determined in 1972 by X-ray analysis of its N-acetyl derivative. [555] Later, the presence of anatoxin A was detected in a range of other toxic strains of Oscillatoria, Anabaena circinalis, Aphanizomenonflos-aquae, Cylindorsperum pp. and Raphidiopsis mediterranea. 

---