CHARACTERIZATION OF SYNECHOCYSTIS SP PCC-6803 IN IRON-SUPPLIED AND IRON-DEFICIENT MEDIA

The photosynthetic apparatus is rich in iron-containing cofactors and iron deficiency causes severe impairment of photosynthesis in plants, algae, and cyanobacteria. Synechocystis sp. PCC 6803 serves as a model system to investigate the complex assembly and integration of the multi-subunit protein complexes of oxygenic photosynthetic electron transport; particularly when coupled to developmental cues due to nutrient limitation or requirements. We study Fe3+-deficient and Fe3+-supplemented cultures of Synechocystis sp. PCC 6803. The autotrophic growth rate of Fe3+-deficient cultures is slower than Fe3+-supplemented cultures. Whole cell spectral analysis reveals differences in both the quantity and the peak absorbance of chlorophyll. Fe3+ deficiency decreases rates of photosynthetic electron transport and the mRNA and corresponding protein levels as observed using specific probes. mRNA levels of psaB increased 20-fold during recovery from Fe3+ deficiency, as compared to the control. psaD transcript levels increased to 160% during recovery as compared to the control. PsaA/B heterodimer formation and turnover is dependent on Fe3+ and the complete assembly on the reducing side of photosystem I (PS I) is PsaD-dependent. Recovery from Fe3+ deficiency suggests that regulation occurs at both the mRNA and protein level.