Description of Gloeomargarita ahousahtiae sp. nov. (Gloeomargaritales), a thermophilic cyanobacterium with intracellular carbonate inclusions

A unicellular cyanobacterium, strain VI4D9, was isolated from thermophilic microbial mats thriving in a hot spring of the Ahousaht territory of Vancouver Island, Canada, and characterized using optical and electron microscopy, genome sequencing and cultivation approaches. The cells were elongated rods (5.1 mu m in length and 1.2 mu m in width, on average). Their UV visible absorption spectra revealed that they contain chlorophyll a, phycocyanin and carotenoids. Transmission electron microscopy showed the presence of thylakoids concentrated on one side of the cells. The strain grew within a temperature range of 37-50 degrees C, with an optimum growth at 45 degrees C. Its genome had a size of 3 049 282 bp and a DNA G + C content of 51.8 mol%. The cells contained numerous intracellular spherical granules easily visible under scanning electron microscopy. Energy dispersive X-ray spectroscopy revealed that these granules were made of Ca-, Ba- and Sr-containing carbonates. A phylogenetic 16S rRNA gene tree robustly placed this strain as sister to several environmental sequences and the described species Gloeomargarita lithophora, also characterized by the possession of intracellular carbonate inclusions. We consider strain VI4D9 to represent a new Gloeomargarita species based on its marked phenotypic differences with G. lithophora, notably, its thermophilic nature and different thylakoid organization, therefore we propose the name Gloeomargarita ahousahtiae sp. nov. The type strain is VI4D9 (Culture Collection of Algae and Protozoa strain 1472/1; Laboratorio de Algas Continentales Mexico strain LAC 140). Gloeomargarita ahousahtiae is the second species described within the recently discovered order Gloeomargaritales.