Germination of Microsporidian Spores: The Known and Unknown

New insights into the effects of UV light on individual Nosema bombycis spores, as determined using single-cell optical approaches

Nosema bombycis (Nb) is a pathogen causing pebrine in sericulture. Ultraviolet (UV) light exposure is a common physical disinfection method, but the mechanisms underlying UV-based disinfection have only been studied at the population level. In this study, changes in and germination of UV-irradiated spores were observed using Raman tweezers and phase-contrast imaging to evaluate the effects of UV radiation on Nb spores at the single-cell level. We found that irradiation caused the complete leakage of trehalose from individual spores. We also found that more spores leaked as the UV dose increased. There was no significant loss of intracellular biomacromolecules and no marked changes in the peaks associated with protein secondary structures. Low-dose radiation promoted spore germination and high-dose radiation decreased the germination rate, while the germination time did not undergo significant alterations. These results suggest that UV radiation disrupts the permeability of the inner membrane and alters the spore wall, thereby affecting the ability of the spore to sense and respond to extracellular stimuli, which further triggers germination and reduces or stops spore germination. This study provides new insights into the molecular mechanisms underlying conventional disinfection measures on microsporidian spores.

E. hellem Ser/Thr protein phosphatase PP1 targets the DC MAPK pathway and impairs immune functions

Microsporidia are difficult to be completely eliminated once infected, and the persistence disrupts host cell functions. Here in this study, we aimed to elucidate the impairing effects and consequences of microsporidia on host DCs. Enterocytozoon hellem, one of the most commonly diagnosed zoonotic microsporidia species, was applied. In vivo models demonstrated that E. hellem-infected mice were more susceptible to further pathogenic challenges, and DCs were identified as the most affected groups of cells. In vitro assays revealed that E. hellem infection impaired DCs' immune functions, reflected by down-regulated cytokine expressions, lower extent of maturation, phagocytosis ability, and antigen presentations. E. hellem infection also detained DCs' potencies to prime and stimulate T cells; therefore, host immunities were disrupted. We found that E. hellem Ser/Thr protein phosphatase PP1 directly interacts with host p38α (MAPK14) to manipulate the p38α(MAPK14)/NFAT5 axis of the MAPK pathway. Our study is the first to elucidate the molecular mechanisms of the impairing effects of microsporidia on host DCs' immune functions. The emergence of microsporidiosis may be of great threat to public health.

Insights into the differential molecular response of non-germinated and germinated spores of Ameson portunus in vitro by comparative transcriptome analysis

Ameson portunus, the recently discovered causative agent of "toothpaste disease" of pond-cultured swimming crabs in China has caused enormous economic losses in aquaculture. Understanding the process of spore germination is helpful to elucidate the molecular mechanism of its invasion of host cells. Here, we obtained mature and germinating spores by isolation and purification and in vitro stimulation, respectively. Then, non-germinated and germinated spores were subjected to the comparative transcriptomic analysis to disclose differential molecular responses of these two stages. The highest germination rate, i.e., 71.45 %, was achieved in 0.01 mol/L KOH germination solution. There were 9,609 significantly differentially expressed genes (DEGs), with 685 up-regulated and 8,924 down-regulated DEGs. The up-regulated genes were significantly enriched in ribosome pathway, and the down-regulated genes were significantly enriched in various metabolic pathways, including carbohydrate metabolism, amino acid metabolism and other metabolism. The results suggested that spores require various carbohydrates and amino acids as energy to support their life activities during germination and synthesize large amounts of ribosomal proteins to provide sites for DNA replication, transcription, translation and protein synthesis of the spores of A. portunus within the host cells. Functional genes related to spore germination, such as protein phosphatase CheZ and aquaporin, were also analyzed. The analysis of transcriptome data and identification of functional genes will help to understand the process of spore germination and invasion.