Functional Characterization Of ECFσ Factors Of The Cyanobacterium Synechocystis Sp.PCC6803 In The Stress Conditions

The molecular mechanism of organisms adapting to the environment was the signal transduction and stress response. The cells felt the environmental stress, and generated a stress signal. The signal was transferred to the intracellular through a series of signal transduction mechanism. Then the cells responded at the level of gene, protein and metabolism for surviving in the environment better. Extra cytoplasmic function(ECF) σ factor played a significant role in the process of cellular signal transduction. It was the σ factor that was involved in the transmembrane signal transduction. After the outer membrane received the stress signal, the bound ECF σ factor was released into the cytoplasm, which was involved in the process of gene transcription. Synechocystis sp. strain PCC6803 was the model organism researching stress response, whose genome contained three ECF σ factors: sigG(slr1545), sigH(sll0856) and sigI(sll0687). The function of these ECF σ factors in stress response was unknown. In this study, we constructed 13 sigI mutants using different knock-out strategy. Then the physiological phenotype of sigI mutant and sigH mutant in certain stress condition was researched. The conclusions were as followed.Firstly, the physiological phenotype of sigI mutant was studied in the medium with 1.5%(v/v) ethanol. The results showed that the mutant had better tolerance than the wild type, which indicating that the sigI gene played a special role in the ethanol stress of Synechocystis sp. strain PCC6803.Secondly, the genome of GT-G, which was a wild type strain of Synechocystis sp. strain PCC6803 isolated from ATCC27184, was sequenced using the high-throughput sequencing method. Eight unique mutations belonged to GT-G were found. Among the eight mutations, five non-synonymous mutations might affect its phenotyoe.Thirdly, the physiological phenotype of sigH mutant was studied in the mixotrophic culture under different illumination intensity. We found that the sigH mutant had a lower rate of growth and glucose utilization than the wild type. The photosynthesis-related pigments content in the sigH mutant also reduced. Meanwhile, the rate of growth and glucose utilization in WT increased and in the sigH mutant decreased in the high light intensity. The results illustrated that the sigH gene made sense in the state of Synechocystis sp. strain PCC6803 in the mixotrophic culture. Besides, the impact was related with the illumination intensity.Finally, the physiological phenotype of sigH mutant was discussed in cold stress. The study showed that the growth of the sigH mutant was inhibited. However, there was no difference between the mutant and the WT in the normal light condition. The results indicated that the sigH gene played an important role in the process of Synechocystis sp. strain PCC6803 responding the double stress of high light and cold.This research was the basis of further study to explore the molecular mechanism of organism adapting to environmental stress and develop the genetically engineered photoautotrophic bacteria used for the industrial production of biofuels.