Duddingtonia flagrans, a nematode-eating fungus, is an effective component of animal parasitic nematode biocontrol agents. In the dried formulation, the majority of spores are in an endogenous dormant state. This study focuses on dormant chlamydospore and non-dormant chlamydospore of D. flagrans to investigate the differences in cAMP and protein content between the two types of spores. In this study, cAMP and soluble proteins were extracted from the non-dormant chlamydospore and dormant chlamydospore of D. flagrans isolates SDH035 and DH055, respectively. The cAMP Direct Immunoassay Kit and Bradford protein concentration assay kit (Coomassie brilliant blue method) were used to detect the cAMP and protein content in two types of spores. Results showed that the content of cAMP in dormant spores of both isolates was significantly higher than that in non-dormant spores (p<0.05). The protein content of dormant spores in DH055 bacteria was significantly higher than that of non-dormant spores (p<0.05). In addition, the protein content of dormant spores of the SDH035 strain was slightly higher than that of non-dormant spores, but the difference was not significant (p>0.05). The results obtained in this study provide evidence for the biochemical mechanism of chlamydospore dormancy or the germination of the nematophagous fungus D. flagrans.

The morphological and structural differences of different types of chlamydospore of Duddingtonia flagrans, a nematophagous fungus, were studied under light microscope and electron microscope to provide reference for the biological control of parasitic nematodiasis. In this study, D. flagrans isolate F088 dormant chlamydospore and non-dormant chlamydospore were selected as the research objects. The structural differences of these spores were observed by optical microscopy through lactol cotton blue, Trypan blue and MTT staining. FUN-1, DAPI and CFW staining were used to observe the metabolic activity, cell wall and nucleus differences of the two types of spores under fluorescence microscope. Ultrastructure of the two kinds of spores was observed using scanning electron microscope (SEM) and transmission electron microscope (TEM). Since lacto phenol cotton blue, trypan blue staining cannot distinguish dormant spores from dead spores, MTT assay was performed. Fluorescence microscopy observation showed that the cytoplasmic metabolic activity of non-dormant spores was stronger than that of dormant spores. The nucleus of dormant spores was bright blue, and their fluorescence was stronger than that of non-dormant spores. The cell wall of non-dormant spores produced stronger yellow-green fluorescence than that of dormant spores. Ultrastructural observation showed that there were globular protuberances on the surface of the two types of spores, but with no significant difference between them. The inner wall of dormant spore possesses a thick zona pellucida with high electron density which was significantly thicker than that of non-dormant spores, and their cytoplasm is also changed. In this study, the microstructure characteristics of dormant and non-dormant chlamydospores of D. flagrans fungi were preliminarily clarified, suggesting that the state of cell wall and intracellular materials were changed after spores entered to dormancy.