Metabolic comparison of aerial and submerged mycelia formed in the liquid surface culture of Cordyceps militaris

Abstract

An entomopathogenic fungus, Cordyceps sp. has been known to produce cordycepin which is a purine nucleoside antimetabolite and antibiotic with potential anticancer, antioxidant and anti‐inflammatory activities. Interestingly, Cordyceps militaris produces significantly higher amount in a liquid surface culture than in a submerged culture. The liquid surface culture consists of mycelia growing into the air (aerial mycelia) and mycelia growing toward the bottom into the medium (submerged mycelia). In this study, to clarify roles of aerial and submerged mycelia of C. militaris in the cordycepin production the difference in metabolism between these mycelia was investigated. From transcriptomic analyses of the aerial and submerged mycelia at the culture of 5, 12 and 19 days, the metabolism of the submerged mycelia switched from the oxidative phosphorylation to the fermentation pathway. This activated the pentose phosphate pathway to provide building block materials for the nucleotide biosynthetic pathway. Under hypoxic conditions, the 5‐aminolevulinic acid synthase (CCM_01504), delta‐aminolevulinic acid dehydratase (CCM_00935), coproporphyrinogen III oxidase (CCM_07483) and cytochrome c oxidase 15 (CCM_05057) genes of heme biosynthesis were significantly upregulated. In addition, the liquid surface culture revealed that metabolite coproporhyrinogen III and glycine, the product and precursor of heme, were increased at 12th day and decreased at 19th day, respectively. These results indicate that the submerged mycelia induce the activation of iron acquisition, the ergosterol biosynthetic pathway, and the iron cluster genes of cordycepin biosynthesis in a hypoxic condition. Even though, the expression of the cluster genes of cordycepin biosynthesis was not significantly different in both types of mycelia.

Hypoxia is regulating enzymatic wood decomposition and intracellular carbohydrate metabolism in filamentous white rot fungus

“…Based on the large number of upregulated genes shared between "Spruce + board anaerobic" and "Malt extract" cultivations, we concluded that the submerged mycelium might encounter hypoxia under non-agitated conditions. Similar outcome was recently reported for the Ascomycota species Cordyceps militaris [48]. This is consistent with minor ethanol accumulation detected from liquid media under aerobic cultivations.…”

Improving Hypoxia Adaption Causes Distinct Effects on Growth and Bioactive Compounds Synthesis in an Entomopathogenic Fungus Cordyceps militaris

“…This explains why C. militaris cultivated in pupae had a high content of cordycepin. In addition, it is consistent with the fact that static submerged liquid fermentation can obtain a higher yield of cordycepin than liquid fermentation with ventilation does (Suparmin et al, 2017(Suparmin et al, , 2019. Static liquid fermentation also induced hypoxia stress in the cells of these submerged mycelia.…”

“…However, the functions of hypoxia and its regulators have not been well investigated in C. militaris. In a previous study, only increased expression levels of the genes involved in the ergosterol biosynthetic pathway were reported in hypoxic submerged mycelia, but not of genes encoding SREBPs (Suparmin et al, 2019). Therefore, the investigation of exogenous vgb and endogenous SREBPs-related genes is helpful to better understand the regulatory role of hypoxia stress in the growth and biosynthesis of bioactive compound in C. militaris.…”

Effects of Cordycepin in Cordyceps militaris during Its Infection to Silkworm Larvae

“…Thus, cordycepin and other secondary metabolites may be important for fungal growth in larvae. Our previous paper shows that the expression of CCM_01285 decreased in aerial and submerged mycelia during cordycepin production in the static cultivation of C. militaris [ 14 ]. The expression of CCM_01285 may be unrelated to cordycepin production.…”

“…More cordycepin is produced in static than in submerged culture. Transcriptomic analysis indicates that hypoxic conditions in static cultivation may be required for the production of cordycepin [ 13 , 14 ]. This result suggests that cordycepin is produced in vivo in the hemocoel of silkworms during the infection.…”