Ascosphaera apis spores containing a dark-colored pigment infect honeybee larvae,resulting in a large-scale collapse of the bee colony due to chalkbrood disease.However,little is known about the pigment or whether it ...Ascosphaera apis spores containing a dark-colored pigment infect honeybee larvae,resulting in a large-scale collapse of the bee colony due to chalkbrood disease.However,little is known about the pigment or whether it plays a role in bee infection caused by A.apis.In this study,the pigment was isolated by alkali extraction,acid hydrolysis,and repeated precipitation.Ultraviolet(UV)analysis revealed that the pigment had a color value of 273,a maximum absorption peak at 195 nm,and a high alkaline solubility(7.67%)and acid precipitability.Further chemical structure analysis of the pigment,including elemental composition,Fourier transform infrared(FTIR)spectroscopy,Raman spectroscopy,mass spectrometry,and nuclear magnetic resonance(NMR),proved that it was a eumelanin with a typical indole structure.The molecular formula of melanin is C10H6O4N2,and its molecular weight is 409 Da.Melanin has hydroxyl,carboxyl,amino,and phenolic groups that can potentially chelate to metal ions.Antioxidant function analyses showed that A.apis melanin had a high scavenging activity against superoxide,hydroxyl,and 2,2-diphenyl-1-picrylhydrazyl(DPPH)radicals,and a high reducing ability to Fe3+.Indirect immunofluorescence assay(IFA),scanning electron microscopy(SEM),and transmission electron microscopy(TEM)analyses showed that A.apis melanin was located on the spore wall.The spore wall localization,antioxidant activity,and metal ion chelating properties of fungal melanin have been suggested to contribute to spore pathogenicity.However,further infection experiments showed that melanin-deficient spores did not reduce the mortality of bee larvae,indicating that melanin does not increase the virulence of A.apis spores.This study is the first report on melanin produced by A.apis,providing an important background reference for further study on its role in A.apis.展开更多
基金supported by the Science and Technology Project of the Chongqing Municipal Education Commission(No.KJZD-K202100502)the Natural Science Foundation Project of Chongqing(No.cstc2021jcyj-msxm X0422)+4 种基金the Higher Education Teaching Reform Research Project of the Chongqing Municipal Education Commission(Nos.213132 and KJ173061)the Postgraduate Education and Teaching Reform Research Project of Chongqing Normal University(No.xyjg21012)the Creation&Research Team in College and Universities of Chongqing Municipal Education Commission(No.CXQT21013)the College Student Innovation and Entrepreneurship Training Program Project of the Chongqing Municipal Education Commission(No.202110637013)the Natural Science Foundation Project of Chongqing Normal University(No.13XLB009),China。
文摘Ascosphaera apis spores containing a dark-colored pigment infect honeybee larvae,resulting in a large-scale collapse of the bee colony due to chalkbrood disease.However,little is known about the pigment or whether it plays a role in bee infection caused by A.apis.In this study,the pigment was isolated by alkali extraction,acid hydrolysis,and repeated precipitation.Ultraviolet(UV)analysis revealed that the pigment had a color value of 273,a maximum absorption peak at 195 nm,and a high alkaline solubility(7.67%)and acid precipitability.Further chemical structure analysis of the pigment,including elemental composition,Fourier transform infrared(FTIR)spectroscopy,Raman spectroscopy,mass spectrometry,and nuclear magnetic resonance(NMR),proved that it was a eumelanin with a typical indole structure.The molecular formula of melanin is C10H6O4N2,and its molecular weight is 409 Da.Melanin has hydroxyl,carboxyl,amino,and phenolic groups that can potentially chelate to metal ions.Antioxidant function analyses showed that A.apis melanin had a high scavenging activity against superoxide,hydroxyl,and 2,2-diphenyl-1-picrylhydrazyl(DPPH)radicals,and a high reducing ability to Fe3+.Indirect immunofluorescence assay(IFA),scanning electron microscopy(SEM),and transmission electron microscopy(TEM)analyses showed that A.apis melanin was located on the spore wall.The spore wall localization,antioxidant activity,and metal ion chelating properties of fungal melanin have been suggested to contribute to spore pathogenicity.However,further infection experiments showed that melanin-deficient spores did not reduce the mortality of bee larvae,indicating that melanin does not increase the virulence of A.apis spores.This study is the first report on melanin produced by A.apis,providing an important background reference for further study on its role in A.apis.
