EFFECTS OF IRON AND LIGHT STRESS ON THE BIOCHEMICAL COMPOSITION OF ANTARCTIC PHAEOCYSTIS SP. (PRYMNESIOPHYCEAE). I. INTRACELLULAR DMSP CONCENTRATIONS

Abstract

Iron is essential for phytoplankton growth, as it is involved in many metabolic processes. It controls photosynthesis as well as many enzymatic processes. As such, iron affects the cell’s energy supply and contributes to the assimilation of carbon and nitrogen. To determine whether iron limitation would result in energy stress or induced nitrogen deficiency, an Antarctic Phaeocystis sp. (Prymnesiophyceae) strain was studied for its biochemical composition, with the main emphasis on intracellular production of dimethylsulfoniopropionate (DMSP). DMSP is suggested to replace nitrogen containing solutes under conditions of nitrogen deficiency. Batch cultures of Antarctic Phaeocystis sp. were grown under iron‐rich and iron‐poor conditions and simultaneously subjected to high and low light intensities. Iron depletion induced chlorosis and suppressed growth rates as well as the maximum yield of the cultures; these effects were reinforced by low light intensities. Cell volumes were strongly reduced under iron‐limited conditions. However, this reduction in cell volume was accompanied by a reduced DMSP content only in cultures experiencing low light intensities. Under high light conditions, no reduction of DMSP was observed; hence, intracellular DMSP concentrations increased. These observations are discussed relative to carbon and nitrogen metabolism and the biosynthetic pathway of DMSP. It is argued that under high light, low iron conditions, the cells were bordering on nitrogen deficiency induced by iron limitation, whereas under low light, low iron conditions, the cells were energy limited resulting in overall suppressed metabolic rates. Between treatments, DMSP to chlorophyll‐a ratios varied by a factor of 5, demonstrating the dependence of this parameter on the physiological state of the cell.

Comparative functional characteristics of DMSP lyases extracted from polar and temperate Phaeocystis species

“…Intracellular DMSP concentrations in Phaeocystis sp. are typically in the 100 to 300 mM range (Stefels & van Leeuwe 1998). These concentrations are well above the K m values that we determined, suggesting that lyase activity in Phaeocystis sp.…”

“…Colonial Phaeocystis species form massive blooms in both temperate and polar regions and substantially impact the yield of commercially important marine products (Schoemann et al 2005). Phaeocystis blooms play a major role in the biogeochemical cycle of carbon and sulfur by fixing a large amount of carbon dioxide and by producing high concentrations of DMSP and DMS (Stefels & van Leeuwe 1998, van Duyl et al 1998, Arrigo et al 1999, DiTullio et al 2003, and by providing an important substrate for bacterial carbon demand (Rellinger et al 2009). …”

Environmental constraints on the production and removal of the climatically active gas dimethylsulphide (DMS) and implications for ecosystem modelling

“…Shifting from unlimited towards limited growth in a batch culture, cell volume often reduces under nitrogen and iron limitation and stays constant under phosphate limitation. Therefore, an increased intracellular DMSP concentration under N or Fe limitation is at least partly due to a reduction in cell volume (Bucciarelli and Sunda 2003;Keller et al 1999a;Stefels and van Leeuwe 1998).…”

Dimethylsulfoniopropionate (DMSP) and its relation to algal pigments in diverse waters of the Belize coastal lagoon and barrier reef system

“…Among eukaryotic algal groups, dinoflagellates, haptophytes (prymnesiophytes), chrysophytes, pelegaphytes, and prasinophytes typically contain high concentrations of DMSP, while diatoms, cryptomonads, chlorophytes, and euglenophytes often contain little or no DMSP (Keller et al 1989). In addition, a number of environmental factors, including light intensity, solar UV radiation, and availability of limiting nutrients can influence DMSP concentrations within individual algal species (Stefels & van Leeuwe 1998, Keller et al 1999, Sunda et al 2002, Bucciarelli & Sunda 2003.…”