[Inversion of phototaxis in cells of Synechocystis sp. PCC 6803 determined by a mutation in the regulatory gene prqR].

Phototaxis, positive (movement toward the light source) or negative (from the light source) mediates the adaptation of cyanobacteria to varying wave lengths and illumination intensity. The transcription regulator PrqR of the family TetR is known as a repressor of the prqRA operon controlling resistance to the oxidative stress inducer methyl viologen in the cyanobacterium Synechocystis sp. PCC6803. However, it was shown in this work that mutation prqRL17Q affecting the DNA-binding domain of the PrqR protein, which causes derepression of the prqRA operon and enhances cell resistance to methyl viologen, additionally determines negative phototaxis induced with daylight and red light of low intensity. The inactivation of gene prqA did not affect cell motility in mutant PqR carrying mutation prqRL17Q and in the wild-type strain characterized by positive phototaxis appearing in response to the light of low intensity. Moreover, a mutant with deletion prqR did not differ from the wild-type strain with respect to phototaxis type suggesting that the specificity of the regulator protein was changed in cells carrying prqRL17Q mutation. Note that changes in transcription of pilA genes that control biogenesis of pili providing for cell motility were not detected in mutant PqR, and, in agreement with data of atomic force microscopy, the type of pili formation is identical in prqR mutants and the wild-type strain. Meanwhile, mutant PqR manifested a decrease in transcription of gene taxD1 encoding the photoreceptor of red light that is required for the positive phototaxis of cyanobacteria. These data imply that mutation prqRL17Q changes the specificity of the PrqR repressor protein and thereby affects the regulation of phototaxis at the level of photoperception and signal transduction in cells.

[The prqA and mvrA genes encoding carrier proteins control resistance to methyl viologen in the cyanobacterium Synechocystis sp. PCC6803]. / Geny prqA i mvrA, kodiruiushchie belki-transportery, kontroliruiut ustoichivost' k metilviologenu u tsianobakterii Synechocystis sp. PCC6803.

Derivatives with insertional inactivation of prqA and mvrA genes were obtained and studied in the Synechocystis sp. PCC6803 wild-type strain and in the mutant Prq20 resistant to methyl viologen (MV). It was shown that the formation of resistance to MV is associated with the operation of two systems: constitutive and inducible. The prqA gene encoding drug efflux proteins controls the constitutive system of cell resistance to MV. Derepression of the prqA gene is the main reason for an enhanced MV resistance in the Prq20 mutant with impaired repressor function of the PrqR protein. The mvrA gene encoding the transmembrane protein from the family of transporters of sugar and other compounds controls the inducible MV resistance. It is assumed that the MvrA protein is required for efficient elimination from cells of toxic substances formed upon oxidative stress or participates in the repair of membranes destroyed by oxidants. The data obtained demonstrated for the first time that transport systems are involved in the formation of MV resistance in photosynthetic organisms.