First report of Ameson portunus (microsporidia) infection in earthen pond-cultured mud crab, Scylla paramamosain (Decapoda: Portunidae) in China, causing mass morbidity

Development and Evaluation of a Rapid Visualisation Detection Method for Ameson portunus Based on RPA-LFD

The Ameson portunus is a prevalent pathogen affecting Portunus trituberculatus, which can infect P. trituberculatus and cause albinism, seriously damaging its economic value. Therefore, there is a pressing need for an efficient detection platform to rapidly and sensitively identify A. portunus. In this study, we have developed a method known as recombinase polymerase amplification combined with lateral flow dipstick (RPA-LFD) for the swift detection of A. portunus. Three sets of specific primer pairs and a probe were designed according to the spore wall protein (SWP) sequence of A. portunus, in which one of the primer pair (ApSWP-F1/R1) showed the best amplification effects. The optimal reaction temperature was ultimately determined to be 39°C and the optimal reaction time was set at 10 min after careful optimisation of both variables. The sensitivity of the RPA-LFD method was better than that of polymerase chain reaction (PCR), with a limit of 1.71 × 10-4 ng/μL. This RPA-LFD detection method has good specificity for the detection of A. portunus, and tests for other parasites such as Zschokkella ophiocephali, Myxobolus drjagini, Myxidium lieberkuhni and Pelteobagrus fulvidraeo are negative. The above results show that the RPA-LFD detection method of A. portunus established in this study has strong specificity, high sensitivity, simple operation and visual results, which can be widely used for rapid detection on site.

Non-coding RNAs and regulatory networks involved in the Ameson portunus (Microsporidia)-Portunus trituberculatus interaction

Ameson portunus, the causative agent of "toothpaste disease" in Portunus trituberculatus and "slurry-like syndrome" in Scylla paramamosain, has resulted in considerable economic losses in the marine crab aquaculture industry in China. Practical control strategies are yet unavailable. Non-coding RNAs (ncRNAs) are crucial components of gene regulation of intracellular parasites, however, their roles in regulating the microsporidia-host interaction remain limited. Here we conducted a whole-transcriptome RNA-seq analysis to identify ncRNAs and to establish the interaction regulatory networks to get further insights into the A. portunus-P. trituberculatus interaction. Totally, 2805 mRNAs, 484 lncRNAs, 5 circRNAs, and 496 miRNAs were identified from A. portunus. These ncRNAs are possibly important regulators for its own energy and substrate metabolism, thereby supporting the intracellular survival and proliferation of A. portunus. DNA replication-associated mRNAs were significantly up-regulated after P. trituberculatus infection with A. portunus. It can be hypothesized that up-regulated lncRNAs may be responsible for the up-regulation of these DNA replication-related genes by miRNAs in P. trituberculatus. The downregulation of metabolic pathways is one of possible strategies of P. trituberculatus to respond the infection of A. portunus. Cross-species miRNAs were suggested to play important roles in the cross-talk of P. trituberculatus-A. portunus, e.g. the disruption of the cytoskeletal organization and normal cell function of host by this microsporidian. The results enrich the knowledge of ncRNAs in microsporidia and offer new insights into microsporidia-host interactions.

Overcoming research challenges: In vitro cultivation of Ameson portunus (Phylum Microsporidia)

Ameson portunus is an intracellular pathogen that infects marine crabs Portunus trituberculatus and Scylla paramamosain, causing significant economic losses. However, research into this important parasite has been limited due to the absence of an in vitro culture system. To address this challenge, we developed an in vitro cultivation model of A. portunus using RK13 cell line in this study. The fluorescent labeling assay indicated a high infection rate (∼60 %) on the first day post-infection and quantitative PCR (qPCR) detection demonstrated successful infection as early as six hours post-inoculation. Fluorescence in situ hybridization (FISH) and qPCR were used for the detection of A. portunus infected cells. The FISH probe we designed allowed detection of A. portunus in infected cells and qPCR assay provided accurate quantification of A. portunus in the samples. Transmission electron microscopy (TEM) images revealed that A. portunus could complete its entire life cycle and produce mature spores in RK13 cells. Additionally, we have identified novel life cycle characteristics during the development of A. portunus in RK 13 cells using TEM. These findings contribute to our understanding of new life cycle pathways of A. portunus. The establishment of an in vitro culture model for A. portunus is critical as it provides a valuable tool for understanding the molecular and immunological events that occur during infection. Furthermore, it will facilitate the development of effective treatment strategies for this intracellular pathogen.

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.

Differential molecular responses of hemolymph and hepatopancreas of swimming crab, Portunus trituberculatus, infected with Ameson portunus (Microsporidia)

Ameson portunus (Microsporidia) has caused serious economic losses to the aquaculture industry of swimming crab, Portunus trituberculatus. The hemolymph and hepatopancreas are the main immune organs of P. trituberculatus, and the main sites of A. portunus infection. Elucidating the response characteristics of hemolymph and hepatopancreas to microsporidian infection facilitates the development of microsporidiosis prevention and control strategy. This study performed comparative transcriptomic analysis of hemolymph (PTX/PTXA) and hepatopancreas (PTG/PTGA) of P. trituberculatus uninfected and infected with A. portunus. The results showed that there were 223 and 1309 differentially expressed genes (DEGs) in PTX/PTXA and PTG/PTGA, respectively. The lysosome pathway was significantly enriched after the invasion of the hemolymph by A. portunus. Also, immune-related genes were all significantly up-regulated in the hemolymph and hepatopancreas, suggesting that the invasion by A. portunus may activate host immune responses. Unlike hemolymph, antioxidant and detoxification-related genes were also significantly up-regulated in the hepatopancreas. Moreover, metabolism-related genes were significantly down-regulated in the hepatopancreas, suggesting that energy synthesis, resistance to pathogens, and regulation of oxidative stress were suppressed in the hepatopancreas. Hemolymph and hepatopancreas have similarity and tissue specificity to microsporidian infection. The differential genes and pathways identified in this study can provide references for the prevention and control of microsporidiosis.