Preliminary Study On The Biological Activity And Antibacterial Mechanism Of Crude Extracts Of Trichoderma Citrinoviride GF-11 Myceliu

Trichoderma spp.is an important class of biocontrol fungi.In recent years,Trichoderma agents have been widely used in agriculture.Under natural conditions,the role of Trichoderma agents is easily limited by environmental conditions,while Trichoderma fermentation extracts can play a stable antibacterial activity in various environments.Therefore,the study of Trichoderma fermentation extracts and their antifungal mechanisms is helpful to promote the biocontrol application of Trichoderma and the development of microbial preparations.In this study,the fermentation conditions of Trichoderma citrinoviride GF-11 were optimized by single factor and orthogonal experiments to improve the antibacterial activity of the extract of the mycelia.LC-MS/MS technology was used to identify the components in the crude extract of the mycelium,and the antagonistic metabolites in the crude extract of the mycelium were initially obtained.The antibacterial mechanism of Trichoderma citrinoviride GF-11 mycelium extract against Alternaria alternata was revealed by measuring the soluble protein content,malondialdehyde content,DNA degradation,electrical conductivity,and enzyme activity.The results obtained in this study are as follows:1.This study used the antibacterial rate of mycelium extract of Trichoderma citrinoviride GF-11against Alternaria alternata as an indicator,the fermentation conditions were optimized by a single factor experiment and an orthogonal experiment.The liquid content was 20%,the inoculation amount was 0.6%,and the bacterial age was 84 hours.After adding 0.5%KH₂PO₄,0.5%Mg Cl₂·6H₂O,0.5%Ca Cl₂,and 1%Tween-80 to the basic culture medium,the antibacterial rate of Trichoderma citrinoviride GF-11 mycelium extract against Alternaria alternata was the highest at 90.7%,compared to before optimization,it has increased by 21.3%.2.This study analyzed the composition of mycelium extract by LC-MS/MS and found that the extract contained five new peptides among seventy-one peptides and 451 compound,including flavonoids and organic acids,etc.3.The inhibition results of the mycelium extract against pathogens showed that the antibacterial rate of the extract is 90.7%against Alternaria alternata,83.5%against Alternaria tenuissima,and52.6%against Golovinomyces cichoracearum.Meanwhile,the inhibition ratio of the extract is85%against conidia of Alternaria alternata,but the antibacterial effect of the extract on the bacteria is weaker.4.Finally,studying the antibacterial mechanism showed that the extract can cause plasmolysis and swelling of the mycelium,and leading to the leakage of electrolytes and macromolecules by the destruction of the cell membrane.It can also degrade genomic DNA,and reduce the enzyme activity of the metabolic system.In summary,this study used single-factor test and orthogonal experiment to obtain the mycelium extract with good antibacterial activity,and got the antifungal mechanism of the fungus by a range of experiments.It laid a foundation for studying the field application of Trichoderma citrinoviride GF-11.