Temperature adaptations of Cordyceps militaris, impact of host thermal biology and immunity on mycosis development

Topical Infection of Cordyceps militaris in Silkworm Larvae Through the Cuticle has Lower Infectivity Compared to Beauveria bassiana and Metarhizium anisopliae

Topical infection of entomopathogenic fungi in insects occurs when the fungal conidia attach to the insect's surface (cuticle), germinate, and then form appressoria that penetrate the cuticle and enter their bodies. In this study, we inoculated silkworm larvae with three entomopathogenic fungi, Cordyceps militaris, Beauveria bassiana, and Metarhizium anisopliae, and investigated their mechanisms of infection. Attachment of the conidia of the three entomopathogenic fungi to the surface of silkworm larvae was observed under a microscope. We counted the number of conidia attached to the surface of the silkworm larvae and the number of conidia detached from the surface was counted. The number of C. militaris conidia that attached to the surface was less than that of B. bassiana and M. anisopliae; however, it germinated and formed appressoria on hydrophobic surfaces, similar to the other two strains. Mycelial growth of C. militaris was inhibited compared to that of B. bassiana in PDA medium containing 0.1% linoleic and linolenic acids. The germination of C. militaris conidia was also inhibited in PD medium containing 0.1% linoleic or linolenic acids. These results suggest that the attachment of low numbers of C. militaris conidia on the surface of silkworm larvae and presence of inhibitory linoleic or linolenic acids in the silkworm cuticles may cause low topical infectivity by C. militaris. This study improves the efficacy of topically infecting silkworms with C. militaris to produce fungal fruiting bodies for use in traditional Chinese medicine and dietary supplement production.

A review on polysaccharide biosynthesis in Cordyceps militaris

Cordyceps militaris (C. militaris) is an edible parasitic fungus with medicinal properties. Its bioactive polysaccharides are structurally diverse and exhibit various metabolic and biological activities, including antitumor, hypoglycemic, antioxidant, hypolipidemic, anti-inflammatory, immunostimulatory, and anti-atherosclerotic effects. These properties make C. militaris-derived polysaccharides a promising candidate for future development. Recent advancements in microbial fermentation technology have enabled successful laboratory cultivation and extraction of these polysaccharides. These polysaccharides are structurally diverse and exhibit various biological activities, such as immunostimulatory, antioxidant, antitumor, hypolipidemic, and anti-atherosclerotic effects. This review aims to summarize the structure and production mechanisms of polysaccharides from C. militaris, covering extraction methods, key genes and pathways involved in biosynthesis, and fermentation factors that influence yield and activity. Furthermore, the future potential and challenges of utilizing polysaccharides in the development of health foods and pharmaceuticals are addressed. This review serves as a valuable reference in the fields of food and medicine, and provides a theoretical foundation for the study of polysaccharides.

Environment-host-parasite interactions in mass-reared insects

The mass production of insects is rapidly expanding globally, supporting multiple industrial needs. However, parasite infections in insect mass-production systems can lower productivity and can lead to devastating losses. High rearing densities and artificial environmental conditions in mass-rearing facilities affect the insect hosts as well as their parasites. Environmental conditions such as temperature, gases, light, vibration, and ionizing radiation can affect productivity in insect mass-production facilities by altering insect development and susceptibility to parasites. This review explores the recent literature on environment-host-parasite interactions with a specific focus on mass-reared insect species. Understanding these complex interactions offers opportunities to optimise environmental conditions for the prevention of infectious diseases in mass-reared insects.

Optimization of a solid culture medium based on Monochamus alternatus for Cordyceps militaris fruiting body formation

Monochamus alternatus (Coleoptera: Cerambycidae; M. alternatus), popularly known as the Japanese pine sawyer, is a vector of pinewood nematode (Bursaphelenchus xylophilus) that causes pine wilt disease. A solid medium culture with M. alternatus produced Cordyceps militaris fruiting bodies with the longest strips and the highest biological efficiency. Supplementing the original form of M. alternatus with oats resulted in slightly enhanced fruiting body production. The original form of M. alternatus showed higher production than its powder form. The solid culture medium was optimized using a response surface methodology, and the optimal medium contained the following: 8·5 g per bottle of M. alternatus and 11·5 g per bottle of oats mixed with 22·4 ml of water in a 300-ml cylindrical plastic bottle. The optimal culturing period for the fruiting body formation was 37·1 days. Under these conditions, a fruiting body dry weight of 38·0 g per bottle (actual value) was attained. The fruiting body produced using a solid culture medium based on M. alternatus had a cordycepin content of about 25 µg g^-1 . The solid culture medium containing M. alternatus is highly efficient and eco-friendly, and its effectiveness in large-scale fruiting body production from C. militaris has been demonstrated.

Homologous overexpression of genes in Cordyceps militaris improves the production of polysaccharides

The maximum yield of EPS produced by mutant CM-pgm-H was 4.63 ± 0.23 g/L, whereas the yield of wild-type strain was 3.43 ± 0.26 g/L. In addition, the data obtained in the present study indicated that the yield of EPS produced by the engineered strain treated with the co-overexpression of phosphoglucomutase and UDP-glucose 6-dehydrogenase genes achieved 6.11 ± 0.21 g/L, which was increased by 78.13% compared with that by the wild-type strain. CM-pgm-H obtained the highest EPS content than that of gk, ugp, and ugdh mutants. This result indicated that the content of protein phosphoglucomutase was an important influencing factor on the CP production of C. militaris. Furthermore, the EPS production of CM-ugdh-pgm-M was significantly improved by 1.78-fold by co-overexpression. Therefore, our engineering strategies will play an important role in the development of C. militaris for the sustainable production of Cordyceps polysaccharides.

Interplay between Fungal Infection and Bacterial Associates in the Wax Moth Galleria mellonella under Different Temperature Conditions

Various insect bacterial associates are involved in pathogeneses caused by entomopathogenic fungi. The outcome of infection (fungal growth or decomposition) may depend on environmental factors such as temperature. The aim of this study was to analyze the bacterial communities and immune response of Galleria mellonella larvae injected with Cordyceps militaris and incubated at 15 °C and 25 °C. We examined changes in the bacterial CFUs, bacterial communities (Illumina MiSeq 16S rRNA gene sequencing) and expression of immune, apoptosis, ROS and stress-related genes (qPCR) in larval tissues in response to fungal infection at the mentioned temperatures. Increased survival of larvae after C. militaris injection was observed at 25 °C, although more frequent episodes of spontaneous bacteriosis were observed at this temperature compared to 15 °C. We revealed an increase in the abundance of enterococci and enterobacteria in the midgut and hemolymph in response to infection at 25 °C, which was not observed at 15 °C. Antifungal peptide genes showed the highest expression at 25 °C, while antibacterial peptides and inhibitor of apoptosis genes were strongly expressed at 15 °C. Cultivable bacteria significantly suppressed the growth of C. militaris. We suggest that fungi such as C. militaris may need low temperatures to avoid competition with host bacterial associates.

Insect parasites in multicomponent systems and development of new bioinsecticides

Stable and dynamic interactions among plants, herbivorous insects, parasites and associated microbes are formed in natural habitats. The study of these interactions in multicomponent models is required to develop integrated methods for the management of insect pest populations. In this work, we summarize our studies on the influence of different factors, such as hygrothermal conditions, host development, host microbiota, plant quality, and concomitant infections, on interactions between insects and their parasites, such as fungi, bacteria, viruses and parasitoids. Some approaches for developing complex products for biocontrol are also discussed. For example, the use of natural compounds with immunosuppressive effects may enhance the efficacy of microbial agents toward pest insects.

Changes in antifungal defence systems during the intermoult period in the Colorado potato beetle

Susceptibility to the fungus Metarhizium robertsii and changes in host defences were evaluated in different stages of the intermoult period (4-6 h, 34-36 h and 84-86 h post moult in IV larval instars) of the Colorado potato beetle. A significant thickening of the cuticle during larval growth was accompanied by decreases in cuticle melanization, phenoloxidase activity and epicuticular hydrocarbon contents (C28-C32). At the same time, a decrease in the conidial adhesion rate and an increase in resistance to the fungus were observed. In addition, we recorded significant elevation of the encapsulation rate and total haemocyte counts in the haemolymph during the specified period. The activity of detoxification enzymes decreased in the haemolymph but increased in the fat body during larval growth. No significant differences in the fatty acid content in the epicuticle were observed. The role of developmental disorders in susceptibility to entomopathogenic fungi is also discussed.