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.
Spijkerman
Elly
E
Department of Ecology and Ecosystem Modelling, University of Potsdam, Am Neuen Palais 10, Potsdam, Germany. spijker@rz.uni-potsdam.de
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