Screenging Of Active Chemicals Inhibiting Alternaria Alternata And Development Of Fermentation Method

Alternaria alternata is a common filamentous fungus ubiquitous worldwide.As a plant pathogen,A.alternata can infect a number of crops,such as tomato,apple,wheat and tobacco,leading to not only noticeable economic loss but also a pressing threat to human health.In particular,the residues of chemical fungicide used to manage A.alternata have caused serious environmental pollution,damage on animal and human,as well as microbial resistance.Therefore,it is highly desirable to seek novel fungicides that are benign to environment and biodegradable.Although A.alternata infects diverse crops,it can naturally synthesize a panel of economically important metabolites.Hence,it is necessary to determine the fermentation conditions of A.alternata with aiming at bioproduction of high-valued compounds at a large scale.Unfortunately,little is known about the pathogenesis and underlying mechanism biosynthesis of these high-valued compounds in A.alternata.We can identify the key enzymes for biosynthesis of these important metabolites and thus provide a basis for future in-depth study of A.alternata by metabolic analysis.The design and research experiments include the follows:1.This first chapter aims to screen novel green pesticides for the control of A.alternata.In this part,the inhibitory effects of different concentrations of chitosan on A.alternata were investigated.Next,virulence assay was performed to determine the EC50 of chitosan for A.alternata.Results showed that the EC50 was 450 ?g/mL,and chitosan exhibited inhibition against A.alternata,indicating it has potential to serve as a cost-effective fungicide.2.In this chapter,we optimized the fermentation conditions of A.alternata by investigation of cell growth under different rotation speeds,different media and different carbon sources.Results showed that the optimal fermentation conditions include dark cultivation at 28?,120 rpm,liquid potato media with sucrose as a carbon source.Notably,the fermentation cost is relatively low under the aforementioned conditions.3.Currently,the underlying mechanisms of the chitosan against A.alternata and biosynthesis of economically important compounds remain unclear and deserves in-depth exploration.In this chapter,the analysis of the metabolic network of A.alternata was first carried out and we identified the synthesis and degradation pathways of sphingosine and the synthesis pathway of Tenuazonic acid.Next,we pointed out the rate-limiting enzymes,SPT,SPHK and AHAS in the metabolic pathways.Afterwards,the homology analysis between the SPT and AHAS genes was made,and the homology of SPT and AHAS encoding genes was obtained.Then,a phylogenetically related fungi of A.alternata was found by the construction of phylogenetic trees.Eventually,in all probability,we predicted the unreported gene encoding SPHK through the homologous alignment of the fungal genes,and its homology has been determined.In conclusion,the above bioinformatics analysis offers a basis for further research on morphological research and bioproduction of the aforementioned metabolites.