Some Observations on the Fine Structure of a Thermophilic, Acidophilic Alga

Cyanidium caldarium is a thermophilic, acidophilic alga with a cell d iameter of ca. 3 #. It has generally been assigned to the Cyanophyta (blue-green algae) bu t on the basis of morphology, p igment content, and life history, Hirose (2) suggested tha t it should be assigned to the R h o d o p h y t a (red algae). Cyanidium grows, respires, and photosynthesizes optimally at pH 2.0 to 3.0, and at 55°C. (1). Because of its small size, disputed taxonomic position, and remarkable physiological characteristics, the fine structure of this organism is of part icular interest. The cells were grown in a mineral nu t r i en t med ium conta ining 2 per cent glucose at pH 2.0 (liquid) or 5.8 (agar slants) at a l ight intensity of 150 to 250 foot-candles. Cells were fixed for 30 minutes in an unbuffered solution of 5 per cent K M N O 4 at room temperature . Fixation was also a t tempted with a variety of procedures employing buffered osmium tetroxide. The material was dehydra ted in alcohol at room tempera ture and embedded in an Araldite mixture containing 5 per cent plasticizer. The plasticizer was added to permit centrifugation of the cells after Araldite