Study On Iron Deficiency To Slow Down The Toxicity Of NaHSO₃ On PS? And Improve The Growth Of Cyanobacteria

As the fourth largest element in the earth's crust,iron is vital to any life on earth.The biological importance of iron is that as a cofactor,iron participates in various biochemical processes in different forms.Iron is very important for photosynthetic organisms,and iron is an important element in the complex involved in photosynthesis.When photosynthetic organisms are in the state of rapid growth and efficient photosynthesis,a large amount of iron is needed for the synthesis,turnover,repair and electron transport of photosynthetic complexes to ensure the normal operation of photosynthesis.Therefore,when growing rapidly and with high light efficiency,iron deficiency is extremely disadvantageous and even causes death.However,when photosynthetic organisms grow slowly and have low photosynthetic efficiency,excessive iron accumulation will lead to iron poisoning.This is mainly because too much iron can trigger the Fenton reaction,which produces reactive oxygen species?ROS?,which threatens the survival of cells.A large number of literatures have shown that the treatment of algae cells with low concentration of NaHSO₃ can effectively increase the efficiency of photosynthesis.However,when algale cells were treated with medium and high concentration of NaHSO₃,the efficiency of photosynthesis was significantly decreased.So,what role does the change of iron content play in this environment is still unknown so far?In this paper,the model organism Synechocystis sp.strain PCC 6803 was used as the research object to further understand the effects of intracellular iron deficiency on the growth and photosynthesis of cyanobacteria in the presence of NaHSO₃.It was further revealed that under the condition of reducing sulfur such as NaHSO₃,the effect of the change of iron content on the growth and photosynthesis of Synechocystis sp.strain PCC 6803.The main results are summarized as follows:?1?In the presence of NaHSO₃,the iron deficiency mutant was used as the experimental material.We detected the overall photosynthetic efficiency by oxygen electrode,and found that under the condition of rich iron,the photosynthetic oxygenevolution capacity of Synechocystis sp.strain PCC 6803 decreased significantly,which also meant that the photosynthetic capacity of Synechocystis sp.strain PCC6803 was decreased.The accumulation of main subunits of each complex involved in photosynthesis was analyzed by Western blotting.We found that except for PsbO subunits,there were no significant differences among other subunits.In other words,in the presence of NaHSO₃,the target affected by iron change may be located on PS?,and may specifically affect the PsbO subunit,or the oxygen evolution complex?OEC?where the PsbO subunit is located.The physiological function activity was detected by oxygen electrode and chlorophyll fluorescence.We found that iron enrichment inhibited the production of photosynthetic electrons and reduced the photosynthetic activity of PS? to some extent.This further implies that the chemical reaction in which iron is involved may play a key role.And the chemical reaction can produce harmful substances and affect the growth and photosynthesis of Synechocystis sp.strain PCC 6803?2?After searching a large number of literatures,we finally determined that the Fenton reaction,which can be participated in by Fe²⁺,plays a key role.Based on the reaction formula of Fenton reaction,we detected the content changes of substrate and product of Fenton reaction in Synechocystis sp.strain PCC 6803 cells.It is further clarified that iron deficiency is beneficial to the growth of Synechocystis sp.strain PCC 6803.Iron deficiency slowed down the occurrence of Fenton reaction,which in turn reduced the production of hydroxyl radicals.Finally,the damage of hydroxyl radical to the oxygen evolution complex was weakened and the cleavage ability of the oxygen evolution complex to water was stabilized.The photosynthetic activity of PS? was improved,which was beneficial to the growth and photosynthesis of Synechocystis sp.strain PCC 6803.?3?To understand the growth status of Synechocystis sp.strain PCC 6803 by detecting the growth curve.We found that in the presence of NaHSO₃,cell-collecting algae 6803 showed slow growth and decreased chlorophyll content.At the same time,we also found that the growth of Synechocystis sp.strain PCC 6803 under iron deficiency condition was significantly better than that of Synechocystis sp.strain PCC6803 under normal iron condition.To sum up,in the environment of reducing sulfur such as NaHSO₃,we further realize that iron enrichment seems to be disadvantageous in this environment.A large amount of available iron will produce a large amount of hydroxyl radicals through theFenton reaction,which will damage the photosynthesis of cyanobacteria.However,the emergence of oxygen not only produces toxic reactive oxygen molecules,but also reduces the content of reducing iron in the ocean to a certain extent.The reaction of oxygen with reductive iron not only consumes both of them,but also slows down the occurrence of Fenton reaction and reduces the production of reactive oxygen molecules to some extent.If oxygen does not react with reduced iron,the photosynthesis of cyanobacteria may be more toxic and even lead to the death of cyanobacteria,which in turn affects the evolution of species on Earth.These results will further enrich people's understanding of the effect of the reduction of available iron on cyanobacteria and provide an important theoretical reference for understanding the antioxidant mechanism of effective photosynthesis in early cyanobacteria.