Ecophysiological Studies on the Red Alga Galdieria sulphuraria Isolated from Southwest Iceland

Abstract

The acido- and thermophilic red alga, Galdieria sulphuraria, was isolated from three volcanic areas of the Reykjanes peninsula (southwest Iceland). These sites showed pH values of 1.5 to 3, low concentrations of dissolved organic carbon, and were apparently exclusively colonized by the red alga. No other eucaryotes were observed by light or electron microscopy. The isolated Galdieria strains grew heterotrophically on various sugars and polyols. At all three sites, Galdieria occupied terrestrial habitats. Extensive endolithic growth of the alga was only observed at one site where cell layers were found as deep as 3 cm within rocks of geyserite, a soft white siliceous mineral. Light is apparently insufficient for photosynthesis > 10 mm below the stone surface. It is proposed that cells deep within the rock make use of metabolites released by decaying cells in the surroundings. Cells isolated from these algal layers exhibited sugar uptake rates indicative for a low-level heterotrophic state. Therefore, the extraordinary heterotrophic capabilities of Galdieria seem to be especially important in endolithic habitats.

Key words

Cryptoendolithic growth - Cyanidium caldarium - Galdieria sulphuraria - heterotrophy - sulfur springs - geyserite