Journal Article

Phosphorus acquisition by <i>Chlamydomonas acidophila</i> under autotrophic and osmo-mixotrophic growth conditions

Elly Spijkerman

in Journal of Experimental Botany

Published on behalf of Society for Experimental Biology

Volume 58, issue 15-16, pages 4195-4202
Published in print December 2007 | ISSN: 0022-0957
Published online November 2007 | e-ISSN: 1460-2431 | DOI: http://dx.doi.org/10.1093/jxb/erm276

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Chlamydomonas acidophila Negoro is a green algal species abundant in acidic waters where inorganic phosphorus (Pi) and carbon (CO2) are considered the most important growth-limiting nutrients for the phytoplankton. This paper describes the Pi uptake and growth kinetics under varying carbon supply by cultivating the alga autotrophically, with and without CO2 aeration, and osmo-mixotrophically with glucose under low Pi conditions at pH 2.7. The low minimum cellular phosphorus quota (Q0; ranging from 0.6 to 1.1 mmol P mol−1 C) suggested Pi-limiting conditions under all different modes of carbon supply, and was lowest under CO2-aerated conditions. The threshold Pi concentration for growth did not vary from zero, suggesting no detectable metabolic costs. Maximum Pi-uptake rates (Vmax) were a better indication of Pi limitation when compared with the affinity constant for Pi uptake (Km), as Vmax was only high under Pi-limited conditions whereas Km was low under both Pi-limited and Pi-replete conditions. Osmo-mixotrophic growth conditions did not result in decreased extracellular phosphatase activity, but often resulted in physiological characteristics comparable with CO2-aerated cells, suggesting intracellular CO2 production by glucose respiration. In addition, at low CO2 and in autotrophic conditions, C. acidophila had a higher Q0, lower dissolved organic carbon concentration, lower maximum Pi-uptake rates, and lower phosphatase activity, suggesting that growth was co-limited by CO2 and Pi. Furthermore, cells may respond physiologically to both nutrient limitations simultaneously.

Keywords: Acidophilic algae; Chlamydomonas acidophila; CO2; co-limitation; extremophile; glucose; growth; osmo-mixotrophy; phosphatase activity; P limitation

Journal Article.  5144 words.  Illustrated.

Subjects: Plant Sciences and Forestry

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