Life at High Temperatures
by Thomas D. Brock
The biology of acid hot springs is quite different from that of the neutral/alkaline springs we have already discussed. Photosynthetic procaryotes such as the cyanobacteria are completely absent from acid waters, even when the temperature has dropped to quite low values. Instead, the photosynthetic microorganisms of such acid waters are rare kinds of eucaryotes which are found nowhere else on earth.
The principal alga of hot acid waters is Cyanidium caldarium, an organism of unusual evolutionary ancestry that can grow even when the acidity is one hundred times that of lemon juice. (Cyanidium can actually grow, albeit slowly, at a pH of zero!) A photomicrograph of Cyandium cells is shown below.
Photomicrograph of Cyanidium caldarium
The upper temperature limit for Cyanidium is about 56 degrees C (133 degrees F), lower than that of the cyanobacteria (as would be expected, since Cyanidium is a eucaryote). This alga is most conspicuous in warm acid streams such as those of the Porcelain Basin of Norris, or Nymph Creek, a large acid creek that flows into Nymph Lake on the Mammoth-Norris road (see photo below).
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