FIG. 3.

Growth and As(V) formation by the Cyanidiales alga isolate CCMEE 5508. •, growth in the presence of 20 μM As(III); ○, growth in the absence of As(III); □, As(V) accumulated as a result of As(III) oxidation. No As(III) oxidation occurred in uninoculated controls or in killed controls (results not shown). Data represent the mean of duplicate cultures, and error bars (where visible) represent the range of the two values. The thermoacidophilic alga used in this work was grown at 42°C under constant illumination from cool-white fluorescent lamps (80 μE·m⁻²·s⁻²) in Allen medium (1) amended to contain 250 μM phosphate and 20 μM As(III) in closed serum bottles with headspace containing filter (0.2 μm)-sterilized CO₂ (100% initial concentration). As controls, serum bottles containing uninoculated medium or autoclave-killed cells were included, with the headspace of each connected to that of the inoculated serum bottle via sterile Tygon tubing. This precaution was taken to verify that the Sb(III) oxidation observed in these experiments was not abiotic auto-oxidation due to the photosynthetically derived O₂ produced by the algae.