Euglenoids in Rio Tinto, light microscopy footage. These are euglenoid algae, common in extreme environments where they feed on bacteria. Two red pigment spots are used to detect the Sun, and the algae then use their flagella to move towards the sunlight. The Rio Tinto is a highly acidic river located in south-western Spain. It flows through an area rich in minerals, and contains extremophile bacteria that feed on iron and sulphide minerals, creating an acidic environment. Despite the toxic environment, this river contains many microbe species.