Antifungal activity of chitosan against Aspergillus ochraceus and its possible mechanisms of action

Chitosan is a polysaccharide with a wide-range antimicrobial spectrum and has been shown to be effective in control postharvest diseases of various fruit, but the possible mode of action is far from well known. In this study the antifungal activity of chitosan was tested on A. ochraceus and its possible mechanisms involved were also investigated both at microstructure and transcriptome level. Here, we found that chitosan could significantly inhibited spore germination and mycelia growth of A. ochraceus. Scan electron microscopy (SEM) and transmission electron microscopy (TEM) observations showed that chitosan induced remarkable changes in morphology and microstructure of hyphae, such as shriveling, abnormal branching and vacuolation. Changes in expression profiles of A. ochraceus upon chitosan treatment were analyzed by RNA sequencing and a total of 435 differentially expressed genes (DEGs) were identified. Further KEGG analysis revealed that DEGs involved in ribosome biogenesis were down-regulated, while DEGs related to membrane homeostasis, such as glycerophospholipid metabolism, ether lipid metabolism and steroid biosynthesis, were up-regulated. Chitosan may affect the growth and development of A. ochraceus by impairing the integrity of cell surface architecture and protein biosynthesis. These findings have practical implications with respect to the use of chitosan as an alternative way for controlling fungal pathogens.