Study On The Inhibitory Effects Of Aspergillus Flavus Growth By 1-Octanol And 1-Nonanol

Aspergillus flavus is a common spoilage fungus in moldy grains and their derived foods.The proliferation of A.flavus will deteriorate the quality and quantity of cereals grains and produce carcinogenic secondary metabolites aflatoxin,which poses a risk to human and animal health.Take sustainable and effective measures to control the growth of A.flavus in postharvest are critical to ensure the storage safety of grains and their derived foods.Exploitation of active ingredients from biogenic volatile organic compounds as natural gas fungicides has significant potential in controlling fungal decay in postharvest agricultural products.Straight fatty alcohols are a group of volatile fatty acid derivative,which are volatile organic compounds commonly produced from cereal grains during storage.However,their inhibitory effects on the growth of spoilage fungi of stored grain have rarely been reported.In this study,the inhibitory effects of linear fatty alcohols on A.flavus were studied.The results showed that 1-octanol and 1-nonanol could effectively inhibit the growth of A.flavus.Secondly,the controlling effectiveness of 1-octanol and 1-nonanol fumigation on A.flavus proliferation in grains were studied under simulated storage condition.Furthermore,the inhibitory mechanisms of 1-octanol and 1-nonanol on A.flavus were investigated through the physiological,biochemical,metabolomic,and transcriptomic analysis.The plate fumigation method was used to evaluate the inhibitory effects of C2-C9straight-chain fatty alcohol on A.flavus,and the results showed that 1-octanol and 1-nonanol could efficiently inhibit the growth of A.flavus.The minimum inhibitory concentration(MIC)and minimum fungicidal concentration(MFC)of 1-octanol against A.flavus in potato dextrose agar(PDA)were 0.11 μL/m L and 0.27 μL/m L,respectively.The MIC and MFC of1-nonanol against A.flavus in PDA were 0.11 μL/m L and μL/m L,respectively.In the liquid contact experiment,1-octanol and 1-nonanol at a concentration of 0.2 μL/m L can completely inhibit the growth of A.flavus.The results of spore germination experiment showed that the MIC and MFC of 1-octanol on A.flavus spore germination were 1.5 μL/m L and 3.5 μL/m L,respectively.The MIC and MFC of 1-nonanol on A.flavus spore germination were 2 μL/m L and 4 μL/m L,respectively.The results of wheat simulated storage experiments showed that300 μL/L and 352 μL/L of 1-octanol and 1-nonanol could completely inhibit the growth of A.flavus in 20% moisture wheat.Fumigation experiments and wheat simulated storage experiments showed that 1-octanol and 1-nonanol could effectively inhibit the growth of A.flavus at lower concentrations,which had potential application prospects for the prevention and control of A.flavus in stored grain.Subsequently,the inhibitory mechanisms of1-octanol and 1-nonanol on the growth of A.flavus were further studied.The inhibitory mechanism of 1-octanol on the growth of A.flavus were investigated.Treatment with MIC 1-octanol for 8h can damage the integrity of its cell wall and plasma membrane of A.flavus mycelium.Metabolomics analysis showed that 1-octanol treatment significantly changed 74 metabolites in A.flavus mycelium,including 43 up-regulated metabolites and 31 down-regulated metabolites.These metabolites were mainly enriched in the biosynthesis of unsaturated fatty acids,ATP-binding cassette transporters,amino acid metabolism and glycerophospholipid metabolic pathways.1-Octanol induced apoptosis along with morphological abnormalities,phosphatidylserine externalization,mitochondrial membrane potential(MMP)depolarization,intracellular reactive oxygen species(ROS)accumulation,and DNA fragmentation in A.flavus cells.Transcriptome analysis showed that1-octanol treatment caused mitochondrial dysfunction and blocked energy supply in A.flavus spores,interfered with the MAPK signaling pathway,destroyed genetic information transmission processes such as DNA and transcription,induced autophagy pathway,and eventually led to cell death.The inhibitory mechanism of 1-nonanol on the growth of A.flavus was studied.MIC1-nonanol treatment for 6 h could destroyed the membrane integrity of A.flavus mycelia,resulting increased intracellular electrolyte leakage.Metabolomic analysis showed that1-nonanol treatment caused significant changes in 134 metabolites of A.flavus mycelium cells,including 87 up-regulated metabolites and 48 down-regulated metabolites.These metabolites were involved in the tricarboxylic acid cycle,amino acid biosynthesis,protein degradation and absorption,aminoacyl-t RNA biosynthesis,mineral absorption,and in interactions with ABC transporters.Biochemical validation confirmed the disruptive effect of 1-nonanol on A.flavus growth,as indicated by the leakage of intracellular electrolytes,decreased succinate dehydrogenase,mitochondrial dehydrogenase,ATPase activity,and the accumulation of reactive oxygen species.Transcriptomic analysis showed that 1-nonanol treatment mainly affected the expression of genes related to membrane damage,oxidative phosphorylation,DNA replication and autophagy in A.flavus spores.In addition,1-nonanol treatment caused MMP hyperpolarization,ROS accumulation,DNA damage,and ultimately apoptosis.In summary,this study determined the inhibitory effect and antifungal mechanism of1-octanol and 1-nonanol on the growth of A.flavus,which would be helpful for the development and application of biofumigants for postharvest grain management.