IDENTIFICATION AND PHYSIOLOGICAL ASPECTS OF A NOVEL CAROTENOID‐ENRICHED, METAL‐RESISTANT MICROALGA ISOLATED FROM AN ACIDIC RIVER IN HUELVA (SPAIN)¹

Abstract

A heavy‐metal‐resistant, carotenoid‐enriched novel unicellular microalga was isolated from an acidic river in Huelva, Spain. The isolated ribosomal 18S subunit rDNA sequence showed homology with known sequences from green microalgae, the closest sequence (98% homology) belonging to the genus Coccomyxa. The isolated microalga therefore was an up to now uncultured microalga. The microalga was isolated from Tinto River area (Huelva, Spain), an acidic river that exhibits very low pH (1.7–3.1) with high concentrations of sulfuric acid and heavy metals, including Fe, Cu, Mn, Ni, and Al. Electron micrographs show that the microalga contains a large chloroplast with a presence of lipid droplets, an increased number of starch bodies as well as electron‐dense deposits and plastoglobules, the last observed only in iron‐exposed cells. Unlike other acidophile microalgae, the isolated microalga showed high growth rates when cultivated photoautotrophycally (up to 0.6 d−1) in a suitable culture medium prepared at our laboratory. The growth was shown to be iron dependent. When the microalga is grown in fluidized bed reactors, the high growth rates resulted in unexpectedly high productivities for being a microalga that naturally grows in acidic environments (0.32 g·L−1·d−1). The microalga also grows optimally on reduced carbon sources, including glucose and urea, and at an optimal temperature of 35°C. The alga pigment profile is particularly rich in carotenoids, especially lutein, suggesting that the microalga might have potential for antioxidant production, namely, xanthophylls.

Phylogenetic characterization and morphological and physiological aspects of a novel acidotolerant and halotolerant microalga Coccomyxa onubensis sp. nov. (Chlorophyta, Trebouxiophyceae)

“…Darienko et al (2015) recognized this strain as a yet to be described new species with a distinct barcode. Genus affiliation of our strain was already confirmed by a partial 18S rDNA sequence (GU265559; Garbayo et al 2012). Garbayo et al (2012) and Ruíz-Domínguez et al (2015) tentatively designated this strain as Coccomyxa onubensis and Coccomyxa sp.…”

“…Genus affiliation of our strain was already confirmed by a partial 18S rDNA sequence (GU265559; Garbayo et al 2012). Garbayo et al (2012) and Ruíz-Domínguez et al (2015) tentatively designated this strain as Coccomyxa onubensis and Coccomyxa sp. (strain onubensis), respectively, without actually performing phylogenetic analyses and without a formal description.…”

“…Coccomyxa cells were grown in 1-L Erlenmeyer flasks in batch mode. Unless otherwise indicated, the cultures were grown at pH 2.5 in a culture medium based on K9 mineral medium (Silverman and Lundgren 1959), modified according to the following composition: 3.95 g K 2 SO 4 , 0.1 g KCl, 0.5 g K 2 HPO 4 , 0.41 g MgCl 2 , 2.29 g KNO 3 , 0.01 g CaCl 2 , and 5-mL Hutner solution (Hutner et al 1950) in distilled water up to a final volume of 1 L. The Hutner solution was prepared as described in Garbayo et al (2012). The cultures were incubated at 27°C, continuously illuminated at 150 μmol photons m −2 s −1 with white fluorescent lamps, and bubbled with air containing 5 % (v/v) CO 2 .…”

“…Coccomyxa sp. ACCV1 grew well at pH values as low as 2.5 (Garbayo et al 2012), but the optimal pH for high biomass production was not determined. The plasma membrane of extremophile microalgae from lowpH environments shows very low permeability to protons, which allows the cytoplasmatic pH to be kept neutral (Gimmler et al 1988;Gross 2000).…”

“…The microalga Coccomyxa sp. ACCV1, isolated from the acidic waters of Río Tinto (Garbayo et al 2012), has been reported to develop better under cultivation conditions that are different from those typical of the natural acidic aquatic habitat which, for instance, include nitrogen limitation and toxic levels of solved iron and copper (Garbayo et al 2012;Vaquero et al 2012;Ruíz-Domínguez et al 2015). Coccomyxa sp.…”