The Antarctic Chlamydomonas spp. UWO241 and ICE-MDV exhibit differential restructuring of Photosystem I in response to iron
Past studies have shown that the photosynthetic apparatus of a psychrophilic alga C. sp. UWO241 is remodeled to support high rates of Photosystem I (PSI)-associated cyclic electron flow (CEF). Iron levels in ELB are in the nanomolar range; therefore, we hypothesized that PSI restructuring in C. sp. UWO241 may reflect a strategy to survive long-term Fe-deficiency. We studied the effect of Fe availability in C. sp. UWO241, a mesophile, C. reinhardtii, and a second ELB psychrophile, Chlamydomonas sp. ICE-MDV. Under Fe-deficient conditions (2 µM Fe), abundance of the PSI reaction center protein, PsaA, as well as levels of photooxidizable P700 (ΔA820/A820) were significantly reduced in both psychrophiles relative to C. reinhardtii. In response to increased Fe, C. sp. ICE-MDV exhibited increases in PSI 77K Chl a fluorescence and ΔA820/A820 which matched that of C. reinhardtii, while C. sp. UWO241 exhibited moderate restoration of PSI function. Our results indicate that PSI functional organization in C. sp. UWO241 is unique. The unique physiological traits in PSI photochemistry exhibited by the psychrophiles may reflect adaptation to the stratified physicochemical conditions present the shallow vs. deep photic zones of a chemically Antarctic lake.
Sample Processing Protocol
Algal cells were lysed by bead beating with non-ionic detergent supplemented in the lysis buffer. Proteins were denatured in 8M urea and trypsin digested. 75 ug of digested peptides were loaded onto a SCX capillary precolumn, and further separated by a 15 cm C18 capillary column with several fractions before injecting into the Thermo LTQ XL for peptide analysis.
Data Processing Protocol
The two dimensional (2D)-LC-MS/MS was conducted on a LTQ ion trap mass spectrometer operated in the data-dependent acquisition mode by recording the full ass spectra of 300-1700 m/z, and fragment the 5 most abundant peaks of each scan for MS/MS analysis. The MS/MS raw data was analyzed by first converting into MS2 files, followed by database search using ProLuCID. The UWO 241 protein database was generated based on our transcriptomics data supplemented with 37 common contaminants, and their reversed sequences as quality control system to restrain false positive discovery to 0.05. Differentially expressed proteins were analyzed using PatternLab for Proteomics.
Cook G, Teufel A, Kalra I, Li W, Wang X, Priscu J, Morgan-Kiss R. The Antarctic psychrophiles Chlamydomonas spp. UWO241 and ICE-MDV exhibit differential restructuring of photosystem I in response to iron. Photosynth Res. 2019 PubMed: 30729447