Abstract: A thermophilic-acidophilic alga, strains of Cyanidium caldarium, is disclosed as having a very effective external uptake of metals from metal-containing aqueous media. A process is disclosed for producing at least one polysaccharide comprises contacting an acidic aqueous medium containing at least one added metal selected from the group consisting of alkali metals, alkaline earth metals, aluminum and mixtures thereof and at least one acidophilic microorganism at conditions effective for the growth of the microorganism and the production of polysaccharide by the microorganism.