Cyanidium caldarium bacterium. Coloured transmiss- ion electron micrograph (TEM) of a section through an extremophile Cyanidium caldarium bacterium. Three chloroplasts are seen here (blue/green), each showing layered bands (blue) of photosynth- etic pigment. This bacterium is classified under the red algae, but this species has mainly blue pigmentation. This is a photosynthetic, non-motile bacterium which lives in hot, acidic pools and soil, usually around hot springs. It is an acidophile, and can withstand acidity around pH 0, very rare in a living organism. Its optimum growth temperature is around 50 degrees Celsius. Magnification: x8000 at 6x6cm size.