Polyphosphate metabolism in an acidophilic alga Chlamydomonas acidophila KT-1 (Chlorophyta) under phosphate stress Kahoko Nishikawa a,b, * , Haruko Machida b , Yoko Yamakoshi c , Ryo Ohtomo d , Katsuharu Saito d,e,f , Masanori Saito d,g , Noriko Tominaga b a Department of Traumatology and Critical Care Medicine, National Defense Medical College, 3-2 Namiki Tokorozawa, Saitama 359-8513, Japan b Institute of Environmental Science for Human Life, Ochanomizu University, 2-1-1 Otsuka, Bunkyo-ku, Tokyo 112-8610, Japan c Department of Chemistry and Biochemistry, University of California, Santa Barbara, CA 93106-9510, USA d National Institute of Livestock and Grassland Science, Nasushiobara, Tochigi 329-2793, Japan e CREST, Japan Science and Technology Agency, Kawaguchi, Saitama 332-0012, Japan f Graduate School of Science, University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033, Japan g National Institute for Agro-Environmental Sciences, 3-1-3 Kannondai, Tsukuba, Ibaraki 305-8604, Japan Received 24 August 2005; received in revised form 28 August 2005; accepted 29 August 2005 Available online 23 September 2005 Abstract 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 31 P NMR spectroscopy, and enzymatic quantification. The PolyP granules inside of C. acidophila KT-1 cells were observed by microscopy with a fluorescent dye 4 0 ,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. # 2005 Elsevier Ireland Ltd. All rights reserved. Keywords: Polyphosphate metabolism; Phosphate deficient condition; Acidophilic algae; Chlamydomonas; Fluorescent microscopy; In vivo 31 P NMR 1. Introduction Polyphosphate (PolyP) is ubiquitous in nature, and has been found in all organisms so far examined [1–4]. In particular, lower eukaryote such as algae and yeast were reported to accumulate large amount of PolyP [5–13]. These organisms have been regarded as good models for investigation into the function of PolyP. PolyP is an intriguing material with various functions as a phosphorus (Pi) reservoir, as a substitute for ATP in the sugar metabolism [14,15], as a chelator for divalent cations [16,17] and as a factor in regulatory responses to stresses and nutritional deficiencies [18,19]. For example, PolyP was reported to act as a buffering reagent for alkaline stress in a halotolerant alga, Dunaliella salina [7,20]. However, the unexplained fundamental physiological role of PolyP is still under consideration [21]. We have been interested in an acidophilic alga Chlamydo- monas acidophila KT-1, originally isolated from an acidic lake called Katanuma at Miyagi prefecture in Japan. It is reported to accumulate large amounts of PolyP in its cells [22] and demonstrated a strong heavy metal tolerance [23]. PolyP in C. acidophila KT-1 cells was quickly degraded in the presence of high concentrations of cadmium (Cd stress) and simultaneously vacuolar deposits containing Cd and Pi appeared [22]. This PolyP degradation was thought to be related to detoxification of Cd, but the detailed mechanism of this Cd sequestering system www.elsevier.com/locate/plantsci Plant Science 170 (2006) 307–313 * Corresponding author. Tel.: +81 42 995 1888; fax: +81 42 995 8513. E-mail address: kaho@jk9.so-net.ne.jp (K. Nishikawa). 0168-9452/$ – see front matter # 2005 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.plantsci.2005.08.025