Functional Mechanism Analysis Of Hpn1 Reducing The Stress Of NaHSO₃ And Promoting Hydrogen In Cyanobacteria

The excessive use of fossil fuels has made environmental problems increasingly prominent,and it is urgent to find a sustainable and clean energy source.The combustion product of hydrogen is water,which will not cause an environmental pollution and can be recycled.Hydrogen is an ideal energy source in the future.Microalgae hydrogen photoproduction is the process of hydrogenase using electrons generated by PSII to reduce hydrogen protons to form molecular hydrogen.The raw materials used in the microalgae hydrogen photoproduction are water and solar energy.Compared with traditional hydrogen production,microalgae hydrogen photoproduction has obvious advantages.Therefore,the production of hydrogen by microalgae photosynthesis is one of the important ways to solve the problems of energy shortage and environmental pollution.However,microalgae hydrogen photoproduction have to face two problems.First,the hydrogenase is very sensitive to oxygen,and consequently it is very easy to inactivate in the presence of oxygen.Second,hydrogen photoproduction lacks sufficient electrons.Collectively,many researchers use sulfur deficiency or adding NaHSO₃ to reduce oxygen content and promote hydrogen photoproduction.Adding NaHSO₃ to reduce oxygen has been relatively mature,and the accumulation of photosynthetic hydrogen produced by microalgae has also increased significantly.However,the same as the problem faced by the sulfur deficiency,adding NaHSO₃ does harm to cells and the activity of PSII was significantly reduced,limiting the electrons required for hydrogen photoproduction.Therefore,under the background of reducing the oxygen content,it is very important for microalgae to maintain high PSII activity and ensure adequate electrons.At present,under the background of NaHSO₃,PSII activity has been improved by certain physiological methods to promote the microalgae hydrogen photoproduction.Therefore,this thesis attempts to screen mutants with high PSII activity under the background of NaHSO₃ and explain the mechanism of promoting hydrogen photoproduction of Synechocystis 6803.In this thesis,we screened the transposon mutant library of Synechocystis 6803 under the background of NaHSO₃and successfully identified a protein Hpn1?high PSII activity under NaHSO₃?that is resistant to NaHSO₃.Deletion of Hpn1 can reduce the toxicity of NaHSO₃ and promote PSII activity.This research has important theoretical significance for microalgae to achieve a large-scale photosynthetic hydrogen production.The main results are as follows:?1?By screening the transposon mutant library of Synechocystis 6803,we isolated and identified 2 mutant strains,which grow similarly to WT under normal conditions and grow better than WT under the background of NaHSO₃.Reverse PCR analysis showed that both mutants were inserted into the same gene hpn1.Physiological data show that the deletion of hpn1 can increase PSII activity under the background of NaHSO₃.?2?The accumulation of hydrogen production shows that adding NaHSO₃ can increase the accumulation of hydrogen production of Synechocystis 6803,which is in line with the theory of reducing the oxygen content,increasing the PSII activity,ensuring sufficient electrons,and promoting hydrogen production.?3?Transcription level data indicate that Hpn1 interacts with PsbH.Deletion of hpn1 results in up-regulating the psbH transcription level,possibly maintaining the stability of PSII.Under the conditions of hydrogen production,?hpn1 is less damaged than WT,so it is not necessary to mobilize a large amount of PsbH to protect PSII,so the transcription level of psbH expression is down-regulated.In summary,we have successfully identified a protein Hpn1,and its deletion can increase PSII activity and promote photosynthetic hydrogen production in Synechocystis 6803 under the background of NaHSO₃.