A Parachlorella kessleri (Trebouxiophyceae, Chlorophyta) strain from an extremely acidic geothermal pond in Argentina

Abstract

Juárez Á.B., Vélez C.G., Iñiguez A.R., Martínez D.E., Rodríguez M.C., Vigna M.S. and Ríos de Molina M.C. 2011. A Parachlorella kessleri (Trebouxiophyceae, Chlorophyta) strain from an extremely acidic geothermal pond in Argentina. Phycologia 50: 413–421. DOI: 10.2216/10-79.1Acidic geothermal environments are rare and very few organisms can thrive in them. Chlorella or Chlorella-like species have been described in a variety of environments but their presence in extremely acidic waters have rarely been reported. A Chlorella-like alga (strain BAFC CA10) was isolated from Laguna Verde, a volcanic mesothermal acidic pond from northern Patagonia (Argentina). Applying a multimethod approach including microscopic, ultrastructural, chemical and phylogenetic analyses, the acidotolerant strain BAFC CA10 was identified as Parachlorella kessleri ( = Chlorella kessleri) on the basis of comparisons with the authentic strain SAG 211-11g. Our results confirmed the initial characterization of the Laguna Verde strain as C. kessleri, but since this species was transferred to the new genus Parachlorella, strain BAFC CA10 should be designated as P. kessleri. Histochemical staining and sugar composition of the cell-wall amorphous and fibrillar matrix, together with transmission electron microscopy of the cells, showed the distinctive characters of the species: (1) glucosamine was the exclusive component of the fibrillar cell wall; (2) rhamnose, galactose, glucose and xylose together with minor quantities of arabinose, mannose and fucose were present in the cell-wall hemicellulose matrix; (3) there was a single parietal chloroplast surrounding the entire cell with a small aperture (“mantel-shaped”); (4) there was one pyrenoid in the thickening of the chloroplast surrounded by two starch granules and bisected by two thylakoids; and (5) the cell wall was an electron-transparent homogeneous structure 60–80 nm thick. Phylogenetic analyses of concatenated small-subunit and internal transcribed sequence ribosomal DNA sequences of coccoid green algae within the Chlorella and the Parachlorella clades of the Chlorellaceae confirmed that strain BAFC CA10 is unequivocally related to the P. kessleri strains. Our results suggest that P. kessleri should be added to the list of species capable of adapting to live in extremely acidic environments.