Fatty acid profiles and their chemotaxonomy in planktonic species of Anabaena (Cyanobacteria) with straight trichomes
Twenty-four axenic strains of planktonic Anabaena with straight trichomes, assigned to 7 species, were investigated by analyzing the pattern and content of their fatty acid composition, and comparing their fatty acid composition with their morphological properties.
Introduction
Freshwater planktonic cyanobacteria Anabaena spp. are organisms that sometimes form water blooms in eutrophic lakes, reservoirs, and ponds. Like Microcystis species, these filamentous heterocystous cyanobacteria are also recognized as a threat to public health due to the production of toxic substances such as microcystin, anatoxin-a, and saxitoxin. (Carmichael, 1981, Skulberg et al., 1993, Humpage et al., 1994, Chorus and Bartram, 1999) and excretion of geosmin-like odor-producing substances (Izaguirre et al., 1981, Juttner, 1987, Hayes and Burch, 1989). In spite of the ecological significance of planktonic Anabaena, identification is problematic and often provisional (Hickel, 1982, Komarek and Anagnostidis, 1989). The current taxonomy of Anabaena is based mainly on morphological characteristics such as trichome form, shape of akinetes, size of cells, and relative position of the akinetes to heterocysts. According to Geitler (1942) “the determination of Anabaena species is very difficult and frustrating” (cf. Hickel, 1982). Some morphological criteria vary among different researchers (Fritsch, 1949, Nygaard, 1949, Komarek, 1958, Pankow, 1965, Komarkova-Legenrova and Eloranta, 1992, Watanabe, 1992, Niiyama, 1996). Furthermore, taxonomic characters such as filament form and akinete cells are problematic because akinetes are occasionally absent and trichome form may be irreversibly changed by culture conditions. Recently, Castenholz and Waterbury (1989) strongly urged that bacterial approaches should be introduced to the taxonomy of cyanobacteria due to their prokaryotic properties. Therefore, it is apparent that planktonic Anabaena species require more taxonomic studies incorporating not only morphological characters but also physiological, chemical, and genetic features.
Fatty acid composition is a useful analytical tool in bacterial taxonomy (Welch, 1991, Embly and Wait, 1994). In the cyanobacteria, Kenyon, 1972, Kenyon et al., 1972, Murata and Gombos, 1992 proposed that four types of fatty acid composition exist in cyanobacteria and demonstrated some correlations with morphological properties. Caudales and Wells (1992) investigated the cellular fatty acids of benthic cyanobacteria belonging to the genera Anabaena and Nostoc and found significant differences between those genera. Krüger et al. (1995) evaluated the taxonomic importance of fatty acid composition at the genus and subgenus level by analyzing the fatty acid composition of different Microcystis isolates and other members of the order Chroococcales. However, there is little information about fatty acid composition and chemotaxonomy in planktonic species of Anabaena. According to Watanabe, 1992, Watanabe, 1998, planktonic species of Anabaena are divided into two groups: species with straight trichomes and those with coiled trichomes. In the present study, we extensively examined 24 strains with straight trichomes by analyzing the pattern and content of fatty acids in these strains and established their chemotaxonomy by comparing their fatty acid composition with morphological properties.
Section snippets
Results
The 24 strains used in the present study (see Table 1) were identified as 7 species based on morphological observations: Anabaena affinis Lemmermann, A. planctonica Brunnthaler, A. solitaria Klenahn, A. smithii (Komárek) Watanabe, A. viriguri Denis et Fremy, A. kisseleviana Elenkin, A. danica (Nygaard) Komárková et Eloranta. The composition and content of fatty acids in these strains are shown in Table 2. The major components of fatty acids in these strains were 16:0, 16:1(cis-), 18:2, and
Discussion
Fatty acids of cyanobacteria have been investigated for their content, composition types, metabolism, and biotechnological application by different researchers (Cohen et al., 1987, Ahlgren et al., 1992, Murata and Gombos, 1992, Matsunaga et al., 1995). In terms of chemotaxonomy by fatty acid composition, Cohen and Vonshak (1991) indicated that there should be a separation between freshwater and salt-tolerant strains in the genus Spirulina based on the difference in their fatty acid composition.
Organisms and culture conditions
Axenic strains of 24 planktonic Anabaena with straight trichomes were used in the present study. Among these strains, 20 were obtained from different culture collections (NIES, TAC, CCAP, and NIVA; for abbreviations see Table 1), and 4 were isolated by the authors from Japan (Table 1). The unialgal strains were purified into the axenic state using the pipette washing method. Taxonomy of all the strains, based on morphological characteristics, are presented in Li et al. (2001). All the strains
Acknowledgements
We thank Professors T. Hori and I. Inouye, University of Tsukuba, for their critical advice on this study and helpful encouragement. This work was supported by Special Coordination Funds from the Science and Technology Agency (STA) of Japan.
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