The physiological functions of different ferredoxins in Synechocystis sp. PCC 6803
The cyanobacterium Synechocystis possesses nine ferredoxins (Fx) and one flavodoxin (IsiB), which function as electron carriers with low reduction potentials. They participate in a variety of metabolic reactions. In contrast to the highly abundant protein Fx1, which is well studied, the functions of the low-abundant ferredoxins (Fx2-Fx9), are only poorly understood. In this thesis, various ferredoxin/flavodoxin mutants were constructed and studied under different growth conditions. To assign distinct functions to single ferredoxins in deletion mutants is a challenge as most of them can probably replace each other physiologically. A special emphasis was put on the characterization of Δfx9.In this thesis it was found that the bacterial-type Fx9 is probably involved in the nitrogen metabolism in Synechocystis.In summary, the transition of PDHc to PFOR, maybe also of NADH-GOGAT to Fd-GOGAT, suggests that the NADH pool is reduced first under highly reducing conditions and that thereafter electrons are transferred to the ferredoxin pool with a more negative redox potential. Synechocystis cells seem to switch from the utilization of NADH- to ferredoxin-dependent enzymes under highly reducing conditions. Low abundant ferredoxins and especially Fx9 are of physiological importance under these conditions.