Function Analysis Of Alg9 Gene In Beauveria Bassiana

Beauveria bassiana（Bb）,as a model strain of interaction between microorganisms and insects,has been widely used in agricultural pest control.Therefore,the study of Beauveria bassiana has both theoretical and practical significance.However,the effectiveness of fungal insecticides to control field pests is affected by many environmental factors,such as environmental temperature,sunlight ultraviolet radiation,and agricultural compounds.Beauveria bassiana achieves attachment through the interaction of cell wall surface proteins with host cell receptor molecules,which is a key link in infection and disease.At the same time,the cell wall is an important barrier for conidia to resist external stress and evade host defenses.In the N-glycosylation of cell wall proteins,the transfer of mannosyl is mediated by one of the specific glycosyltransferases（Alg9）.However,there are few research reports on N-glycosylation in biocontrol fungi.This article takes the mannose transferase BbAlg9 in the entomopathogenic fungus Beauveria bassiana as the research object to explore the role of this gene in resistance to stress and virulence.It is expected to provide a new strategy for genetically improving strains using resistance-related functional genes and improving the field stability of biocontrol fungal preparations.The main research contents and results are as follows:The knockout and complement strains of BbAlg9 gene were constructed and phenotypic analysis was carried out.Compared with the wild type,the knockout strains showed different degree of defects in sporulation,multiple stress tolerance,virulence,cell wall integrity and transcription level of related phenotypic genes.Among them,the LT₅₀（24.9 min）of the mutant strainΔBbAlg9 was lower than that of the wild strain（54.1 min）under 45℃humidity and heat stress,which decreased by 54%;Under UV-B radiation,the LD₅₀（0.28 J/cm²）of the mutant strainΔBbAlg9 was smaller than that of the wild strain（0.35 J/cm²）,which decreased by 21%;Compared with the control strain,under hyperosmotic stress,the EC₅₀value ofΔBbAlg9 on Na Cl and sorbitol decreased by 14%and 29%;The tolerance to cell wall disrupting agents Congo Red（CR）and Sodium Dodecyl Sulfate（SDS）was also reduced by32%and 22%;The chitin content ofΔBbAlg9 was 62%lower than that of the wild strain,and the conidia hydrophobicity index was 15%lower than that of the wild strain.Through the method of body wall infection and blood cavity injection,the half-lethal time LD₅₀of wild strains against Galleria mellonella larvae were 4.4 days and 4.6 days.In contrast,prolonged LD₅₀means a 30%and 19%decrease in virulence.It can be seen that Alg9 plays an important role in the adaptability of Beauveria bassiana to insect hosts and its environment,especially in cell wall.