Phylogeny and toxicology of Lyngbya wollei (Cyanobacteria, Oscillatoriales) from north-eastern Australia, with a description of Microseira gen. nov.

Abstract

Three populations of the freshwater filamentous cyanobacterium Lyngbya wollei (Farlow ex Gomont) Speziale and Dyck have been putatively identified from north-eastern Australia and found to produce the potent cyanotoxin cylindrospermopsin (CYN) and its analog deoxy-cylindrospermopsin (deoxy-CYN). We investigated the phylogeny and toxicology of strains and mats isolated from two of these populations using a combination of molecular and morphological techniques. Morphologically the strains corresponded to the type description, however, the frequency of false-branching was low, and variable over time. Strains and mat samples from both sites were positive for the cyrF and cyrJ genes associated with CYN biosynthesis. Phylogenetic analysis of these genes from Australian L.wollei sequences and comparable cyanobacterial sequences revealed that the genes in L.wollei were more closely related to homologous genes in Oscillatoria sp. PCC 6506 than to homologs in Nostocalean CYN-producers. These data suggest a common evolutionary origin of CYN biosynthesis in L.wollei and Oscillatoria. In both the 16S rRNA and nifH phylogenies, the Australian L.wollei strains formed well-supported clades with United States L.wollei (= Plectonemawollei) strains. Pair-wise sequence similarities within the 16S rRNA clade containing all eleven L.wollei strains were high, ranging from 97% to 100%. This group was distantly related (<92% nucleotide similarity) to other taxa within the group previously considered under the genus Lyngbya sensu lato (C. Agardh ex Gomont). Collectively, these results suggest that this toxigenic group is evolutionarily distinct and sufficiently distant as to be considered a separate genus, which we have described as Microseira gen. nov. and hence transfer to it the type M.wollei comb. nov.