89 Morphological and molecular characterisation of four nostoc species isolated from desert soils

Abstract

Four unusual strains of Nostoc species from desert soils of the western United States were chosen for morphological and molecular characterization. The morphological characteristics of the desert Nostoc were compared with the species of Nostoc described in the literature. Although our strains were similar to previously described species such as N. punctiforme, N. paludosum, N. commune, N. microscopicum and N. muscorum, they did not fit any of these taxa well when all characters (including ecological preference) were used. The 16S rRNA gene sequences of the strains CM1‐VF10, CM1‐VF14, CNP‐AK1 and JT2‐VF2 were aligned with published Nostoc sequences from GenBank and other desert Nostoc sequenced at John Carroll University. Pseudanabaena, Cylindrospermum sp. and Anabaena spiroides from GenBank were used as outgroups. In addition, the ITS regions of all four desert taxa, a typical Nostoc commune from European temperate soils, Nostoc punctiforme PCC73102 from cycad roots were compared by examining secondary structure. The combined analysis provided compelling evidence that CM1VF10, CM1VF14, and JT2VF2 were species new to science. While CNP‐AK1 (the phycobiont of the desert soil lichen, Collema tenax) had some significant discontinuities from its closest relative, N. punctiforme, we consider the evidence currently insufficient to separate these two strains. The purported phycobiont of this lichen is N. commune, and we have demonstrated that this is incorrect. One of the desert strains (JT2‐VF2) likely represents a new genus. Morphological autapomorphies, distinctive SSU rRNA gene sequence, and differences in secondary structure of the 16S‐23S ITS provide congruent evidence for this conclusion.