@article{SpijkermanGarciaMendozaMatthijsetal.2004,
  author    = {Spijkerman, Elly and Garcia-Mendoza, E. and Matthijs, H. C. P. and Van Hunnik, E. and Coesel, P. F. M.},
  title     = {Negative effects of P-buffering and pH on photosynthetic activity of planktonic desmid species},
  year      = {2004},
  abstract  = {The photosynthetic activities of three planktonic desmid species (Staurastrum brachiatum, Staurodesmus cuspidatus var. curvatus, and Staurastrum chaetoceras) were compared after adaptation to medium enriched with either a 20 mM Na+- phosphate (P) or HEPES buffer. Incubations up to 2 d were carried out at pH 6 or 8 under normal air or air enriched with 5 \% CO2. Gross maximum photosynthetic rate (Pmax) and growth rate were decreased in both S. brachiatum and Std. cuspidatus at higher pH when using the HEPES buffer and this effect was independent of CO2 concentration, indicating that pH had an inhibitory effect on photosynthesis and growth in these species. The P-buffer at pH 8 caused a large decrease in Pmax and quantum yield for charge separation in photosystem 2 (PS2), compared to HEPES-buffered algae. This effect was very large in both S. brachiatum and Std. cuspidatus, two species characteristic of soft water lakes, but also significant in S. chaetoceras, a species dominant in eutrophic, hard water lakes. The decreased Pmax in P- buffer could not be related to a significant increase in cellular P content known to be responsible for inhibition in isolated chloroplasts. Experiments at pH 6 and 8 showed that two conditions, high pH and high Na+ concentration, both contributed to the decreased Pmax and quantum yield in the desmids. Effects of a P-buffer were less pronounced by using K+-P buffer. The use of P-buffer at pH 8 possibly resulted in high irradiance stress in all species, indicated by damage in the PS2 core complex. In the soft water species pH 8 resulted in increased non-photochemical quenching together with a high de-epoxidation state of the xanthophyll cycle pigments.},
  language  = {en}
}
@article{PoerschmannSpijkermanLanger2004,
  author    = {Poerschmann, J{\"u}rgen and Spijkerman, Elly and Langer, Uwe},
  title     = {Fatty acid patterns in chlamydomonas sp as a marker for nutritional regimes and temperature under extremely acidic conditions},
  year      = {2004},
  abstract  = {Fatty acid profiles were used to characterize nutritional pathways in Chlamydomonas sp. isolated from an acidic mining lake (pH 2.7). Surprisingly, profiles of Chlamydomonas sp. grown in the lab under photoautotrophic, mixotrophic, and heterotrophic conditions at in situ deep strata lake water temperatures (8C) were very similar, polyunsaturated fatty acids including a-linolenic acid (18:3x3) and 16:4x3 along with palmitic acid (16:0) being most abundant. Therefore, heterotrophic growth of Chlamydomonas sp. at low temperatures can result in high concentrations of polyunsaturated fatty acids, as previously only described for some psychrophilic bacteria. By contrast, the cultivation of isolated Chlamydomonas sp. at 20C, reflecting surface water temperatures, provided fatty acid patterns characteristic of the nutrition strategy applied: the concentration of polyunsaturated fatty acids decreased when the growth pathway changed from photoautotrophic via mixotrophic to heterotrophic. Total fatty acid concentration also diminished in this order. Principal component analysis confirmed the significance of FA profiling to mirror nutritional pathways. Lake- water analysis revealed low concentrations of dissolved organic carbon, mainly consisting of polymeric fulvic acids that are unable to support heterotrophic growth of Chlamydomonas sp. Polymeric fulvic acids present in the deeper strata of the lake turned out to be formed in situ on the basis of organic monomers including reduced sulfur-containing ones, as revealed by thermochemolysis and pyrolysis. Growth of Chlamydomonas sp. in the deep chlorophyll maximum is therefore assumed to mainly result from photosynthesis, despite very low photon densities. Phytol-including metabolites proved to be significant biomarkers to indicate the nutritional pathway of Chlamydomonas sp. a, x-Dicarboxylic acids{\`u}light- induced degradation products of unsaturated fatty acids{\`u}appeared to be good indicators of photooxidative alterations to the algal species under study.},
  language  = {en}
}
@article{GerloffEliasSpijkermanProschold2005,
  author    = {Gerloff-Elias, Antje and Spijkerman, Elly and Proschold, T.},
  title     = {Effect of external pH on the growth, photosynthesis and photosynthetic electron transport of Chlamydomonas acidophila Negoro, isolated from an extremely acidic lake (pH 2.6)},
  issn      = {0140-7791},
  year      = {2005},
  abstract  = {In extremely acidic lakes, low primary production rates have been measured. We assumed that proton stress might explain these observations and therefore investigated the photosynthetic behaviour of a Chlamydomonas species, a main primary producer in acidic lakes, over a range of pH values. Identified as C. acidophila using small subunit rDNA analysis, this species is identical to other isolates from acidic environments in Europe and South America, suggesting a worldwide distribution. Laboratory experiments with C. acidophila, revealed a broad pH-tolerance for growth and photosynthesis, the lower pH limit lying at pH 1.5 and the upper limit at pH 7. Growth rates at optimum pH conditions (pH 3 and 5) were equal to those of the mesophilic Chlamydomonas reinhardtii. In contrast, photosynthetic rates were significantly higher, suggesting that higher photosynthetic rates compensated for higher dark respiration rates, as confirmed experimentally. Electron transport capacities of PSI and PSII, P700(+) re-reduction times and measurements of PSII fluorescence revealed the induction of alternative electron transport mechanisms, such as chlororespiration, state transitions and cyclic electron transport, only at suboptimal pH values (pH 1.5; 4 and 6-7). The results indicate, that C. acidophila is well adapted to low pH and that the relatively low primary production rates are not a result of pH stress},
  language  = {en}
}
@article{GerloffEliasSpijkermanSchubert2005,
  author    = {Gerloff-Elias, Antje and Spijkerman, Elly and Schubert, H.},
  title     = {Light acclimation of Chlamydomonas acidophila accumulating in the hypolimnion of an acidic lake (pH 2.6)},
  issn      = {0046-5070},
  year      = {2005},
  abstract  = {1. The unicellular green alga Chlamydomonas acidophila accumulates in a thin phytoplankton layer in the hypolimnion (deep chlorophyll maximum, DCM) of an extremely acidic lake (Lake 111, pH 2.6, Lusatia, Germany), in which the underwater light spectrum is distorted and red-shifted. 2. Chlamydomonas acidophila exhibited a significantly higher absorption efficiency and a higher cellular chlorophyll b content when incubated in the red shifted underwater light of Lake 111 than in a typical, blue-green dominated, light spectrum. 3. Chlamydomonas acidophila has excellent low light acclimation properties (increased chlorophyll b content, increased oxygen yield and a low light saturation point for photosynthesis) that support survival of the species in the low light climate of the DCM. 4. In situ acclimation to the DCM under low light and temperature decreased maximum photosynthetic rate in autotrophic C. acidophila cultures, whereas the presence of glucose under these conditions enhanced photosynthetic efficiency and capacity. 5. The adaptive abilities of C. acidophila to light and temperature shown in this study, in combination with the absence of potent competitors because of low lake pH, most probably enable the unusual dominance of the green alga in the DCM of Lake 111},
  language  = {en}
}
@article{SpijkermanMaberlyCoesel2005,
  author    = {Spijkerman, Elly and Maberly, Stephen C. and Coesel, P. F. M.},
  title     = {Carbon acquisition mechanisms by planktonic desmids and their link to ecological distribution},
  issn      = {0008-4026},
  year      = {2005},
  abstract  = {To test if different inorganic carbon (C-i) uptake mechanisms underlie the ecological distribution pattern of planktonic desmids, we performed pH-drift experiments with 12 strains, belonging to seven species, originating from lakes of different pH. Staurastrum brachiatum Ralfs and Staurodesmus cuspidatus (Ralfs) Teil. var. curvatus (W. West) Teil., species confined to acidic, soft water habitats, showed remarkably different behavior in the pH drift experiments: S. brachiatum appeared to use CO2 only, whereas Staurodesmus cuspidatus appeared to use HCO3- as well. Staurastrum chaetoceras (Schr.) Smith and Staurastrum planctonicum Teil, species well-known for their abundant occurrence in alkaline waters, were the most effective at using HCO3-. Other species, to be encountered in both slightly acidic and slightly alkaline waters, took an intermediate position. Experiments using specific inhibitors suggested that Cosmarium abbreviatum Rac. var. planctonicum W. \& G.S. West and S. brachiatum use CO2 by an active CO2 uptake mechanism, whereas S. chaetoceras and Staurodesmus cuspidatus showed an active HCO3- uptake pattern. Most likely, these active uptake mechanisms make use of H+-ATPase, as none of the desmids expressed significant carbonic anhydrase activity. A series of strains of Staurastrum planctonicum isolated from different habitats, all clustered in between the species using HCO3-, but no further differentiation was observed. Therefore, desmids cannot be simply characterized as exclusive CO2 users, and the ecological distribution pattern of a desmid species does not unequivocally link to a certain C-i uptake mechanism. Nevertheless, there does appear to be a general ecological link between a species' C-i uptake mechanism and its ecological distribution},
  language  = {en}
}
@article{Spijkerman2005,
  author    = {Spijkerman, Elly},
  title     = {Inorganic carbon acquisition by Chlamydomonas acidophila across a pH range},
  issn      = {0008-4026},
  year      = {2005},
  abstract  = {Chlamydomonas acidophila Negoro had a higher maximum growth rate upon aeration with 5\% CO2 (v/v) than in nonaerated conditions at an external pH above 2. In medium with a pH of 1.0 or 2.0, a decrease in the maximum growth rate was observed upon CO2 aeration in comparison with nonaerated conditions. At both very low and very high external pH conditions, an induction of external carbonic anhydrase was detected; this being more pronounced in CO2-aerated cells than in nonaerated cells. It is therefore suggested that the induction of carbonic anhydrase is part of a stress response in Chlamydomonas acidophila. Comparison of some physiological characteristics of Chlamydomonas acidophila acclimated at pH 2.65 and at pH 6.0, revealed that CO2 aeration increased gross maximum photosynthesis at both pHs, whereas respiration, light acclimation, and photoinhibition were not effected. At pH 2.65, Chlamydomonas acidophila was found to have a carbon-concentrating mechanism under nonaerated conditions, whereas it did not under CO2-aerated conditions at pH 6. The affinity for CO2 use in O-2 production was not dependent on CO2 aeration, but it was much lower at pH 6 than it was at pH 2.65. CO2 kinetic characteristics indicate that the photosynthesis of Chlamydomonas acidophila in its natural environment is not limited by inorganic carbon},
  language  = {en}
}
@article{GerloffEliasBaruaMoelichetal.2006,
  author    = {Gerloff-Elias, Antje and Barua, Deepak and M{\"o}lich, Andreas and Spijkerman, Elly},
  title     = {Temperature- and pH-dependent accumulation of heat-shock proteins in the acidophilic green alga Chlamydomonas acidophila},
  issn      = {0168-6496},
  doi       = {10.1111/j.1574-6941.2006.00078.x},
  year      = {2006},
  abstract  = {Chlamydomonas acidophila, a unicellular green alga, is a dominant phytoplankton species in acidic water bodies, facing severe environmental conditions such as low pH and high heavy metal concentrations. We examined the pH-, and temperature-dependent accumulation of heat-shock proteins in this alga to determine whether heat-shock proteins play a role in adaptation to their environment. Our results show increased heat-shock proteins accumulation at suboptimal pHs, which were not connected with any change in intracellular pH. In comparison to the mesophilic Chlamydomonas reinhardtii, the acidophilic species exhibited significantly higher accumulations of heat-shock proteins under control conditions, indicating an environmental adaptation of increased basal levels of heat-shock proteins. The results suggest that heat- shock proteins might play a role in the adaptation of C. acidophila, and possibly other acidophilic algae, to their extreme environment},
  language  = {en}
}
@article{Spijkerman2007,
  author    = {Spijkerman, Elly},
  title     = {Is there really insufficient support for Tilman's R* concept? A comment on Miller et al},
  year      = {2007},
  language  = {en}
}
@article{Spijkerman2007,
  author    = {Spijkerman, Elly},
  title     = {Phosphorus acquisition by Chlamydomonas acidophila under autotrophic and osmo-mixotrophic growth conditions},
  year      = {2007},
  language  = {en}
}
@article{SpijkermanBaruaGerloffEliasetal.2007,
  author    = {Spijkerman, Elly and Barua, Deepak and Gerloff-Elias, Antje and Gaedke, Ursula and Heckathorn, S. A.},
  title     = {Stress responses and metal tolerance of Chlamydomonas acidophila in metal-enriched lake water and artificial medium},
  doi       = {10.1007/s00792-007-0067-0},
  year      = {2007},
  abstract  = {Chlamydomonas acidophila faces high heavy-metal concentrations in acidic mining lakes, where it is a dominant phytoplankton species. To investigate the importance of metals to C. acidophila in these lakes, we examined the response of growth, photosynthesis, cell structure, heat-shock protein (Hsp) accumulation, and metal adsorption after incubation in metal-rich lake water and artificial growth medium enriched with metals (Fe, Zn). Incubation in both metal-rich lake water and medium caused large decreases in photosystem II function (though no differences among lakes), but no decrease in growth rate (except for medium + Fe). Concentrations of small Hsps were higher in algae incubated in metal-rich lake- water than in metal-enriched medium, whereas Hsp60 and Hsp70A were either less or equally expressed. Cellular Zn and Fe contents were lower, and metals adsorbed to the cell surface were higher, in lake-water-incubated algae than in medium- grown cells. The results indicate that high Zn or Fe levels are likely not the main or only contributor to the low primary production in mining lakes, and multiple adaptations of C. acidophila (e.g., high Hsp levels, decreased metal accumulation) increase its tolerance to metals and permit survival under such adverse environmental conditions. Supposedly, the main stress factor present in the lake water is an interaction between low P and high Fe concentrations.},
  language  = {en}
}