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Abstract
Cyanidium caldarium is a primitive acidophilic red alga which grown optimally at pH 1–3. When the alga was cultured at pH 6, which is the upper limit of acidity for its survival, most of the algal cells became large cells with four endospores which did not split into daughter cells. This suggests that the alga survives in the endospore state at pH 6 to protect against nutrient uptake deficiency due to low pH gradient across the cell membranes. The alga was also found to secrete an extracellular protein specifically at pH 6. The protein was identified to be lysyl oxidase‐like protein, which had been reported to be widely distributed in the animal kingdom but not yet found in the plant kingdom. In the plant kingdom, only two primitive acidophilic algae, C. caldarium and Cyanidioschyzon merolae, possess a gene encoding this protein.
Highlights
The transition from prokaryotic cells into eukaryotic cells is important in biological evolution
The order Cyanidiales that consist of three genera Cyanidioschyzon, Cyanidium and Galdieria are the only photosynthetic organisms which have existed for hundreds of millions of years in acidic hot springs (Reeb & Bhattacharya, 2010)
Since the common characteristics of these species are shared with the prokaryotic cyanobacteria and with the eukaryotic Rhodophyta, this makes them good candidates for covering the evolutionary gap between the prokaryotic and eukaryotic cell (Seckbach, 1987)
Summary
The transition from prokaryotic cells into eukaryotic cells is important in biological evolution. Since the common characteristics of these species are shared with the prokaryotic cyanobacteria and with the eukaryotic Rhodophyta (red algae), this makes them good candidates for covering the evolutionary gap between the prokaryotic and eukaryotic cell (Seckbach, 1987) These species show progressive morphological and biochemical steps from primitive cyanobacterial features of Cyanidioschyzon to Cyanidium and to further advanced Galdieria (Seckbach, 1995). The intracellular pH of cells incubated under anaerobic conditions in the dark was acidified as the external pH decreased (Enami et al, 1986) These indicate that when ATP production by either respiration or photosynthesis is suppressed, passive transport of protons into the cells from acidic external medium results in an intracellular acidification. Grau‐Bové, Ruiz‐Trillo, and Rodriguez‐Pascual (2015) have surveyed a wide selection of genomes in order to infer the evolutionary history of LOX(L) and found LOX(L) genomes in animals, and in bacteria and archaea
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