Molecular systematics of the genera Microcystis, Anabaena, and Aphanizomenon of the cyanobacteria
Williams, Charles R. (Charles Robert)
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A phylogenetic analysis of the Genus Microcystis , Order Chroococales, and the Genera Anabaena and Aphanizomenon, Family Nostocaceae, Order Nostocales, within the Division Cyanophyta was conducted using DNA sequences from the gene subunits cpcB and cpcA with intergenic spacer, the rpoC1 gene subunit and the 16S--23S rRNA ITS region. Pacific Northwest lakes were sampled for the above genera to examine regional diversity and determine the position of regional strains.Molecular data confirm that previously recognized species of Microcystis show little divergence and represent 3--4 distinct genotype clusters. Morphological characters appear too plastic to determine relatedness between two distinct Pacific Northwest, U.S.A. strains that can be present in the same lakes.Phylogenetic analyses of the Family Nostocaceae suggest that major taxonomic revision of this family and perhaps the entire Order Nostocales is necessary. The genus Anabaena was polyphyletic with members of the genera Nostoc, Aphanizomenon, Anabaenopsis, Cylindrospermopsis and Fischerella contained within what were previously thought to be good Anabaena groupings based on traditional morphological characterization.At least two major lineages of Anabaena were found by cpcBA-IGS and rpoCI analysis. One clade contained the planktonic strains, A. flos-aquae and A. circinalis , and included the genus Aphanizomenon. It is proposed under the rules of the International Code of Botanical Nomenclature that Aphanizomenon flos-aquae and Aphanizomenon gracile be subsumed within Anabaena flos-aquae. The second major Anabaena clade contained soil and planktonic isolates and seven species as described under the International Code of Botanical Nomenclature. Anabaena strains UTEX(1444), UTEX(2557), UTEX(2558) and UTEX(1823) should be designated as Nostoc.The distribution of planktonic Anabaena in eight lowland Puget Sound lakes appeared limited to 4 genotype clusters representing 6 morphotypes. One Anabaena flos-aquae genotype was found exclusively in the late fall/winter through early spring and was responsible for toxic blooms (anatoxin a). An identical morphotype from the same lake exhibited a significantly different genotype and life history (summer and early fall dominant). Trichome habit, cell, heterocyst and akinete shape and size were shown to be poor characters for distinguishing several genera and many strains but were useful features in distinguishing Anabaena circinalis from Anabaena flos-aquae in the Pacific Northwest.
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