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JXB Advance Access originally published online on November 26, 2007
Journal of Experimental Botany 2007 58(15-16):4195-4202; doi:10.1093/jxb/erm276
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© 2007 The Author(s).
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/2.0/uk/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. This paper is available online free of all access charges (see http://jxb.oxfordjournals.org/open_access.html for further details)

RESEARCH PAPER

Phosphorus acquisition by Chlamydomonas acidophila under autotrophic and osmo-mixotrophic growth conditions

Elly Spijkerman*

Department of Ecology and Ecosystem Modelling, University of Potsdam, Am Neuen Palais 10, Potsdam, Germany

* E-mail: spijker{at}rz.uni-potsdam.de

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.

Key words: Acidophilic algae, Chlamydomonas acidophila, CO2, co-limitation, extremophile, glucose, growth, osmo-mixotrophy, phosphatase activity, P limitation

Received 16 August 2007; Revised 11 October 2007 Accepted 15 October 2007


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