Abstract:

Cordyceps militaris W5 strain was used to investigate changes of colony morphology,cell ultrastructure and reactive oxygen species（ROS）content during successive transfer culture by every eight days,aiming to reveal early external identification markers of degradation. The results showed that the degradation of C. militaris W5 strain was a gradual process. Changes of colony morphology,mycelium and spore morphology began to appear in the third generation during successive transfer culture. Rhythm rings,color changes together with constricted and sunken hyphae were the significant external characteristics of the third generation,which could be considered as early colonial morphology identification marker of degradation in C. militaris W5 strain. During the successive transfer culture of C. militaris W5 strain,the following phenomena gradually occurred:cell walls of mycelia became thinner,cell nucleus became larger,mitochondria swelled and deformed,vacuoles became bigger,lomasomes reduced,spherosome dissolved,fat droplets and osmophilic granules formed. The degradation degree of W5 strain could be estimated by whether nucleolus appeared in cell nucleus,lomasomes appeared in cell,as well as vacuolar fusion and autophagy occurred in cell. From the third generation,color of mycelial cells became deep after NBT staining,indicating the increase of reactive oxygen species content. H₂O₂ content in the third generation was significantly higher than that in the first two generations. Based on the close relationship between mitochondria and reactive oxygen species,it was believed that the deformation and reduction of mitochondria might be an important reason for the degradation of C. militaris W5 strain.

Key words: Cordyceps militaris, successive transfer culture, strain degeneration, cell, ultrastructure, reactive oxygen species