Polyphosphate metabolism in an acidophilic alga Chlamydomonas acidophila KT-1 (Chlorophyta) under phosphate stress

In order to study the polyphosphate (PolyP) metabolism in the acidophilic alga, the effect of rapid change of external phosphate concentration (so-called Pi stress condition) on the distribution of PolyP in Chlamydomonas acidophila KT-1 was investigated by fluorescent microscopy, in vivo 31P NMR spectroscopy, and enzymatic quantification. The PolyP granules inside of C. acidophila KT-1 cells were observed by microscopy with a fluorescent dye 4′,6-diamidino-2-phenylindole (DAPI). Cells transferred from phosphate (Pi) deficient to Pi rich conditions were contained a large amount of PolyP and an additional new PolyP stain was observed around the cell surface. In comparison to a neutrophilic alga Chlamydomonas reinhardtii C-9, the total amount of PolyP in C. acidophila KT-1 was 2.5 times smaller. The lower content of PolyP in C. acidophila KT-1 was supposed to be attributable to the specific properties of its cell membrane, which limited to incorporate phosphate from the environment. Nevertheless, the trend of degradation and re-synthesis of PolyP in C. acidophila KT-1 was similar to that of C. reinhardtii C-9 under Pi stress conditions with absolute PolyP amount being affected by the total phosphate in the cells.