03186nas a2200181   4500008004100000245010400041210006900145260003900214490001000253520255800263653002002821653001602841653002202857653001202879100002102891700002902912856006302941       2014                        eng d00aEnvironmental impacts on RubisCO from green algal laboratory isolates to Antarctic lake communities0 aEnvironmental impacts on RubisCO from green algal laboratory iso  aOxford, OHbMiami Universityc20140 vPh.D.3 a<p>Ribulose-1,5-bisphosphate carboxylase oxygenase (RubisCO) is found in a variety of autotrophic microorganisms ranging from green algae, cyanobacteria, and chemoautotrophic bacteria. As this enzyme has the potential to catalyze carboxylation (carbon fixation) or oxygenation (photorespiration) reactions, it is regulated in response to environmental variables at the levels of transcription, translation, and post-translation by the enzyme, RubisCO activase. A combination of laboratory experiments on green algal isolates and field experiments were utilized to gain insight on carbon fixation in permanently ice-covered Antarctic lakes. RubisCO was investigated as a potential target for cold adaptation of carbon fixation in the psychrophilic green alga, Chlamydomonas raudensis UWO241 (UWO241), isolated from Lake Bonney, Antarctica. RubisCO activity, stability, and whole cell carbon fixation were measured for the psychrophile and compared to a closely related mesophilic alga, C. raudensis SAG49.72 (SAG49.72). The effect of environmental factors including light and temperature on UWO241 and SAG49.72 RubisCO activation state, an indirect measurement of RubisCO activase activity, and abundance was investigated using a modified RubisCO carboxylase assay and immunoblotting, respectively. Lastly, maximum potential RubisCO carboxylase activity was determined using a modified activity assay in multiple ice covered Antarctic lakes including Lake Bonney. This data was complemented with lake depth profiles of enzyme abundance determined by quantitative real-time PCR and RubisCO-harboring organism diversity. While purified RubisCO of the psychrophilic green alga did not function optimally at low temperature, whole cell carbon fixation was greater under such conditions, suggesting that the overall process of carbon fixation is modified to function in UWO241. Increased RubisCO abundance at low temperature may contribute to this phenomenon. Low light levels may be important in regulation of RubisCO via RubisCO activase and should be further investigated. Based on community level RubsiCO activity and enzyme abundance, light and RubisCO harboring organisms including eukaryotic algae and cyanobacteria were positively correlated, but this was variable between lakes. Dark carbon fixation was potentially important in lakes west lobe Bonney and Fryxell and this community was negatively correlated with light. Results of targeted physiology and community level experiments led to development of a carbon fixation model for Lake Bonney.</p>10acarbon fixation10agreen algae10aice-covered lakes10aRubisCO1 aDolhi, Jenna, M.1 aMorgan-Kiss, Rachael, M.  uhttp://rave.ohiolink.edu/etdc/view?acc_num=miami1407056783