Changes in Lipid Composition Induced by Environmental and Genetic Manipulation in Synechocystis sp. PCC 6803
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The objective of this research was to investigate the photosynthetic lipids synthesized by the cyanobacterium Synechocystis sp. PCC 6803 and to develop methods to extract, separate and characterize them. A particular focus has been directed towards the function of isoprenoid quinones and specifically the biosynthesis of plastoquinone, an essential component in photosynthetic and respiratory electron transport chains of cyanobacteria. This pathway differs from that in plants and algae and candidate genes assumed to be involved in this unresolved pathway were identified through in silico analyses. The gene deletion strain Δsll1653 was constructed and characterized to assess whether sll1653 is involved in plastoquinone synthesis or if a shift in the utilization of quinones can be initiated upon depletion of oxygen. The mutant strain had similar growth characteristics to the wild-type but failed to grow on glucose under high light. Spectroscopic and mass spectrometry analyses revealed accumulation of phycobilins and photoprotective carotenoids and tocopherols in the mutant strain. This strain was impaired in phylloquinone synthesis but a significant decrease in plastoquinone levels could not be observed. When the wild-type and mutant strain were subjected to limiting oxygen concentrations, both a state transition from PS II to PS I and an increase in F0 could be observed. Still, anaerobic conditions did not induce the replacement of plastoquinone by phylloquinone in the PQ-pool. The results obtained in this study indicate that the sll1653 gene, encoding a methyltransferase, is not directly involved in the biosynthesis of plastoquinone in Synechocystis sp. PCC 6803.