A new cyanobacterial species of Aliinostoc, A. vietnamicum sp. nov., is recorded in the tropical forest soil from the Cát Tiên National Park, Vietnam. The analysis is based on morphological characters, 16S rDNA phylogeny, ITS secondary structure, and fatty acid composition analysis. Aliinostoc vietnamicum differed from the other species of the genus by the size and shape of vegetative cells, size of akinetes and heterocytes, and presence of granular polyphosphate inclusions in vegetative cells. The evolutionary distance matrix based on the 16S rRNA gene shared 96.2-98.2% similarities with other Aliinostoc sequences. The phylogeny inferred by maximum likelihood and Bayesian inference placed A. vietnamicum in the Aliinostoc clade, within the Nostocaceae. For the first time, fatty acid composition analysis was obtained for a member of the genus Aliinostoc with cultivation time experiments. α-linolenic (27.54-37.75%), palmitic (13.87-22.65%), and stearic (10.08-20.27%) acids were the dominant fatty acids when cultured during the exponential growth phase, as well as during stationary. This is the first finding of a strain with such a high content of stearic acid among cyanobacteria with Nostoc-like morphology.
Keywords: 16S rDNA; Cyanobacteria; ITS secondary structure; fatty acid; new species; phylogeny.
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