Phosphorus acquisition by Chlamydomonas acidophila under autotrophic and osmo-mixotrophic growth conditions.
Chlamydomonas acidophila Negoro is a green algal species abundant in acidic waters where inorganic phosphorus (P(i)) and carbon (CO(2)) are considered the most important growth-limiting nutrients for the phytoplankton. This paper describes the P(i) uptake and growth kinetics under varying carbon supply by cultivating the alga autotrophically, with and without CO(2) aeration, and osmo-mixotrophically with glucose under low P(i) conditions at pH 2.7. The low minimum cellular phosphorus quota (Q(0); ranging from 0.6 to 1.1 mmol P mol(-1) C) suggested P(i)-limiting conditions under all different modes of carbon supply, and was lowest under CO(2)-aerated conditions. The threshold P(i) concentration for growth did not vary from zero, suggesting no detectable metabolic costs. Maximum P(i)-uptake rates (V(max)) were a better indication of P(i) limitation when compared with the affinity constant for P(i) uptake (K(m)), as V(max) was only high under P(i)-limited conditions whereas K(m) was low under both P(i)-limited and P(i)-replete conditions. Osmo-mixotrophic growth conditions did not result in decreased extracellular phosphatase activity, but often resulted in physiological characteristics comparable with CO(2)-aerated cells, suggesting intracellular CO(2) production by glucose respiration. In addition, at low CO(2) and in autotrophic conditions, C. acidophila had a higher Q(0), lower dissolved organic carbon concentration, lower maximum P(i)-uptake rates, and lower phosphatase activity, suggesting that growth was co-limited by CO(2) and P(i). Furthermore, cells may respond physiologically to both nutrient limitations simultaneously.
Department of Ecology and Ecosystem Modelling, University of Potsdam, Am Neuen Palais 10, Potsdam, Germany. spijker@rz.uni-potsdam.de
Elly
E
Spijkerman
D000818:Animals; D052818:Autotrophic Processes / Q000502:physiology*; D002245:Carbon Dioxide / Q000378:metabolism*; D002696:Chlamydomonas / Q000201:enzymology / Q000254:growth & development / Q000378:metabolism*; D046508:Culture Techniques; D005947:Glucose / Q000378:metabolism*; D010744:Phosphoric Monoester Hydrolases / Q000378:metabolism*; D010758:Phosphorus / Q000378:metabolism*
D002245:Carbon Dioxide; D010758:Phosphorus; D010744:Phosphoric Monoester Hydrolases; D005947:Glucose