Establishment of the Cordyceps militaris Degeneration Gradient and Variations in Related Molecular Mechanisms
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Abstract:
Repeated subculture of the Cordyceps militaris strain ZGCM was performed in the laboratory to simulate strain degeneration during industrial cultivation. A gradually degenerated strain line was built over seven generations to explore the morphological changes and internal molecular mechanisms of degeneration. The results showed that strain ZGCM degenerates from the second generation, with no fruiting bodies observed by the sixth generation. The residual sugar in the culture medium is reduced over each generation, with sugar content decreasing by 62.40 % in the fifth generation as compared to the first generation. Furthermore, the residual protein content of the medium increased after the second generation, suggesting that the ability of C. militaris to absorb nitrogen from external sources declines continuously. The transcription levels of 14 differentially expressed genes that were linearly related to C. militaris generation were measured using qRT-PCR. However, only the CCM_04090 gene showed increased expression with each generation, increasing by 39.60 % in the fifth generation as compared to the first generation, which is consistent with previous reports, and no significant changes were observed for other target genes. According to the HPLC results, cordycepin production exhibited a general decline over each generation and, after 30 days of fermentation, fifth generation cordycepin production decreased by 74.56 % as compared to the first generation. The results indicated that strain degeneration has a negative impact on not only the production of fruiting bodies, but also on cordycepin production, both of which are core quality indicators of C. militaris products.
