Quantitative detection and proliferation dynamics of a novel Spiroplasma eriocheiris pathogen in the freshwater crayfish, Procambarus clarkii

Rab7 GTPase, a direct target of miR-131-3p, limits intracellular Spiroplasma eriocheiris infection by modulating phagocytosis

Spiroplasma eriocheiris is a kind of intracellular pathogen without cell wall and the causative agent of Chinese mitten crab Eriocheir sinensis "tremor disease", which causes significant economic losses in the crustacean aquaculture. However, little is known about the intracellular transport of this pathogen and host innate immune response to this pathogen. Rab GTPases are key regulators for endocytosis and intracellular pathogen trafficking. In this study, we showed that S. eriocheiris infection upregulated the transcription of Rab7 through the downregulation of miR-131-3p. Subsequently, both hemocytes transfected with miR-131-3p mimics and hemocytes derived from Rab7 knockdown crabs exhibited reduced phagocytic activities and increased susceptibility to S. eriocheiris infection. Additionally, Rab7 could interact with the cell shape-determining protein MreB3 of S. eriocheiris, and its overexpression promoted S. eriocheiris internalization and fusion with lysosomes, thereby limiting S. eriocheiris replication in Drosophila S2 cells. Overall, these results demonstrated that Rab7 facilitated host cell phagocytosis and interacted with MreB3 of S. eriocheiris to prevent S. eriocheiris infection. Moreover, miR-131-3p was identified as a negative regulator of this process through its targeting of Rab7. Therefore, targeting miR-131-3p might be an effective strategy for controlling S. eriocheiris in crab aquaculture.

Crab microRNA-381-5p regulates prophenoloxidase activation and phagocytosis to promote intracellular bacteria Spiroplasma eriocheiris infection by targeting mannose-binding protein

Mannose-binding lectin plays an essential role in bacteria or virus-triggered immune response in mammals. Previous proteomic data revealed that in Eriocheir sinensis, the mannose-binding protein was differentially expressed after Spiroplasma eriocheiris infection. However, the function of mannose-binding protein against pathogen infection in invertebrates is poorly understood. In this study, a crab mannose-binding protein (EsMBP) was characterized and enhanced the host resistance to S. eriocheiris infection. The application of recombinant C-type carbohydrate recognition domain (CTLD) of EsMBP led to increased crab survival and decreased S. eriocheiris load in hemocytes. Meanwhile, the overexpression of CTLD of EsMBP in Raw264.7 cells inhibited S. eriocheiris intracellular replication. In contrast, depletion of EsMBP by RNA interference or antibody neutralization attenuated phenoloxidase activity and hemocyte phagocytosis, rendering host more susceptible to S. eriocheiris infection. Furthermore, miR-381-5p in hemocytes suppressed EsMBP expression and negatively regulated phenoloxidase activity to exacerbate S. eriocheiris invasion of hemocytes. Taken together, our findings revealed that crab mannose-binding protein was involved in host defense against S. eriocheiris infection and targeted by miR-381-5p, providing further insights into the control of S. eriocheiris spread in crabs.

Hemolymph exosomes inhibit Spiroplasma eriocheiris infection by promoting Tetraspanin-mediated hemocyte phagocytosis in crab

Exosomes released from infected cells are thought to play an important role in the dissemination of pathogens, as well as in host-derived immune molecules during infection. As an intracellular pathogen, Spiroplasma eriocheiris is harmful to multiple crustaceans. However, the immune mechanism of exosomes during Spiroplasma infection has not been investigated. Here, we found exosomes derived from S. eriocheiris-infected crabs could facilitate phagocytosis and apoptosis of hemocytes, resulting in increased crab survival and suppression of Spiroplasma intracellular replication. Proteomic analysis revealed the altered abundance of EsTetraspanin may confer resistance to S. eriocheiris, possibly by mediating hemocyte phagocytosis in Eriocheir sinensis. Specifically, knockdown of EsTetraspanin in E. sinensis increased susceptibility to S. eriocheiris infection and displayed compromised phagocytic ability, whereas overexpression of EsTetraspanin in Drosophila S2 cells inhibited S. eriocheiris infection. Further, it was confirmed that intramuscular injection of recombinant LEL domain of EsTetraspanin reduced the mortality of S. eriocheiris-infected crabs. Blockade with anti-EsTetraspanin serum could exacerbate S. eriocheiris invasion of hemocytes and impair hemocyte phagocytic activity. Taken together, our findings prove for the first time that exosomes modulate phagocytosis to resist pathogenic infection in invertebrates, which is proposed to be mediated by exosomal Tetraspanin, supporting the development of preventative strategies against Spiroplasma infection.

Development and application of the MIRA and MIRA-LFD detection methods of Spiroplasma eriocheiris

The tremor disease (TD) caused by Spiroplasma eriocheiris is the most destructive disease of the Chinese mitten crab, Eriocheir sinensis. This study attempts to construct Multienzyme Isothermal Rapid Amplification (MIRA), a quick and simple nucleic acid amplification method that operates at room temperature. Based on the gene sequences of S. eriocheiris, appropriate amplification primers were constructed and screened in this investigation. Both the relevant specific probe and the chosen specific amplification primers were designed and labeled. The MIRA and MIRA-LFD reaction conditions were then optimized. The result showed MIRA and MIRA-FFD could identify S. eriocheiris at 37 °C in 30 min and 15 min, respectively. To investigate the specificity of MIRA and MIRA-LFD, three Gram-negative bacteria (Bacillus subtilis, Bacillus thuringiensis, and Staphylococcus aureus), three Gram-positive bacteria (Escherichia coli, Aeromonas hydrophila, and Salmonella typhimurium) and S. eriocheiris were selected. The result showed MIRA and MIRA-LFD were highly specific to S. eriocheiris and did not react with other six pathogens. The sensitivities of PCR, MIRA, and MIRA-LFD were then evaluated. The result showed the detection limit of PCR is 1 ng/L whereas the detection limit of MIRA and MIRA-LFD is 10 pg/L. Finally, the established MIRA and MIRA-LFD detection methods had the advantages of being quick, sensitive, and specific for S. eriocheiris detection, as well as not requiring any specialized equipment.

Current Disease Threats for Cultivated Crab Eriocheir sinensis in China

The Chinese mitten crab, Eriocheir sinensis, is a commercially important crustacean in China due to its great commercial value and compatibility in a variety of aquaculture systems. However, increases in its production have been accompanied by the emergence of various diseases affecting yield, profit, and trading potential. In this study, we review the pathogenic agents associated with E. sinensis since the start of its commercial culture. The history of crab cultivation implies that increased pathogen transfer can occur as E. sinensis aquaculture grows because polyculture of E. sinensis with other aquaculture species is a prevalent practice. With this in mind, a special focus of this review is placed on pathogens that were initially discovered in other crustacean species but have since been demonstrated to infect and cause disease in E. sinensis. We expect that this review will not only offer recommendations for disease management in the E. sinensis aquaculture sector but will also advance other crustacean cultivation.

Eriocheir sinensis vesicle-associated membrane protein can enhance host cell phagocytosis to resist Spiroplasma eriocheiris infection

Vesicle-associated membrane protein (VAMP) belongs to the receptor protein on the membrane of the secretory transport vesicle and involves in host immune function. The intracellular pathogen Spiroplasma eriocheiris could cause Eriocheir sinensis tremor disease. In a previous study, it was found E. sinensis VAMP (EsVAMP) was differently expressed in S. eriocheiris infection by proteomics analysis. This study mainly aims at the function of EsVAMP in the process of the S. eriocheiris infection. The length of EsVAMP gene was 1681 bp, which contained a 395 bp open reading frame, 90 bp 5'-non-coding region (UTR) and 1277 bp 3'-UTR. The results of qPCR showed that EsVAMP was expressed highly in hemocytes and nerves, followed by gills, intestines and hepatopancreas, and lowly expressed in heart and muscles. EsVAMP in hemocytes was up-regulated after S. eriocheiris infection. After EsVAMP over-expression and S. eriocheiris infection, the RAW264.7 cell morphology and cell viability of the experiment group were significantly better than the control group. Meanwhile, the copy number of S. eriocheiris in the experiment group was significantly lower than that in the control group. After EsVAMP and pCMV-Cre-mCherry were ligated and transfected into RAW264.7 cells, it was found that EsVAMP and lysosome co-localized. Meanwhile, the phagocytosed inactivated S. eriocheiris number and phagocytosed efficiency in RAW264.7 cells were increased significantly. The interference experiment was carried out by synthesizing EsVAMP dsRNA to verify that the EsVAMP transcriptions were successfully suppressed. The S. eriocheiris copy number and the mortality of crab increased significantly after EsVAMP RNAi and S. eriocheiris infection. Meanwhile, the phagocytosed inactivated S. eriocheiris number and phagocytosed efficiency in hemocytes decreased significantly after EsVAMP RNAi and S. eriocheiris infection. These results showed that VAMP was involved in the cell phagocytosis to resist pathogen infection.

The Eriocheir sinensis calcium/calmodulin-dependent protein kinase II activates apoptosis to resist Spiroplasma eriocheiris infection

Calcium/calmodulin-dependent protein kinase II is a downstream mediator of calcium signalling and participates in the regulation of various cellular physiological functions. In previous studies, the expression of Eriocheir sinensis CaMKII (EsCaMKII) was significantly decreased in the thoracic ganglion after Spiroplasma eriocheiris infection, as shown using TMT-based quantitative proteomic analysis; however, the specific functions of EsCaMKII are still unclear. In this study, the full-length cDNA of EsCaMKII was 3314 bp long, consisting of a 1605 bp open reading frame encoding a protein of 535 amino acids, including a 258 aa serine/threonine protein kinase catalytic domain (EsCaMKII-CD). EsCaMKII is highly transcribed in haemocytes, nerves (thoracic ganglion), gills, and muscles, but lowly transcribed in the hepatopancreas, heart, and intestines. The transcription levels of EsCaMKII were altered in E. sinensis haemocytes after S. eriocheiris infection. After the over-expression of EsCaMKII-CD in RAW264.7 cells, the apoptosis rate of RAW264.7 cells was significantly increased. After the over-expression of EsCaMKII-CD, the morphology of RAW264.7 cells became worse after being infected with S. eriocheiris. Meanwhile, the copy number of S. eriocheiris in RAW264.7 cells was significantly decreased. From 48 h to 96 h after EsCaMKII RNA interference, the transcription levels of EsCaMKII decreased significantly. The transcription of apoptosis genes and cell apoptosis were also inhibited in haemocytes after EsCaMKII RNAi. The knockdown of EsCaMKII by RNAi resulted in significant increases in the copy number of S. eriocheiris and in the mortality of crabs during S. eriocheiris infection. These results indicate that EsCaMKII could promote the apoptosis of E. sinensis and enhance its ability to resist S. eriocheiris infection.

Ophiopogon japonicus inhibits white spot syndrome virus proliferation in vivo and enhances immune response in Chinese mitten crab Eriocheir sinensis

White spot syndrome virus (WSSV) is a fatal pathogen threatening global crustacean industry with no commercially available drugs to control. Herbal medicines have been widely used to treat a number of viral infections, which could offer a rich reserve for antiviral drug discovery. Here, we evaluated the inhibition activities of 30 herbal medicines against WSSV in Chinese mitten crab Eriocheir sinensis. A WSSV infection model in E. sinensis was firstly established in order to determine the antiviral effects of the plant extracts and to explore the potential action mechanisms. Results showed that the highest anti-WSSV activity was obtained by the treatment of Ophiopogon japonicus extract (93.03%, 100 mg/kg). O. japonicus treatment decreased viral loads in a dose-dependent manner and significantly improved the survival of WSSV-challenged crabs. O. japonicus reduced the expression of vital genes in viral life cycle in vivo, particularly for the immediate-early stage gene ie1. Further results indicated that O. japonicus could repress the JAK-STAT signaling pathway to block ie1 transcription. Moreover, O. japonicus could modulate certain immune genes such as the myosin, toll-like receptor, crustin, and prophenoloxidase in the interactions between WSSV and crabs. The up-regulated expression of pro-autophagic factors (Gabarap and Atg7) and elevated levels of antioxidant enzymes (SOD, CAT and GSH) suggested that O. japonicus may induce autophagy and attenuate WSSV-induced oxidative stress. Taken together, O. japonicus could inhibit WSSV proliferation and improve the survival of WSSV-challenged crabs. Thus, O. japonicus may have the potential to be developed as a preventive or therapeutic agent against WSSV, and its effective compounds merit further isolation and identification.

Microbial pathogens of freshwater crayfish: A critical review and systematization of the existing data with directions for future research

Despite important ecological role and growing commercial value of freshwater crayfish, their diseases are underresearched and many studies examining potential crayfish pathogens do not thoroughly address their epizootiology, pathology or biology. This study reviews over 100 publications on potentially pathogenic viruses, bacteria, fungi and fungal-like microorganisms reported in crayfish and systematizes them based on whether pathogenicity has been observed in an analysed species. Conclusions on pathogenicity were based on successful execution of infectivity trials. For 40.6% of examined studies, microbes were successfully systematized, while for more than a half (59.4%) no conclusion on pathogenicity could be made. Fungi and fungal-like microorganisms were the most studied group of microbes with the highest number of analysed hosts, followed by bacteria and viruses. Our analysis demonstrated the need for: (a) inclusion of higher number of potential host species in the case of viruses, (b) research of bacterial effects in tissues other than haemolymph, and (c) more research into potential fungal and fungal-like pathogens other than Aphanomyces astaci. We highlight the encountered methodological challenges and biases and call for a broad but standardized framework for execution of infectivity trials that would enable systematic data acquisition on interactions between microbes and the host.

An ShK-domain serine protease of Eriocheir sinensis regulates the PO activity to resist Spiroplasma eriocheiris infection

A novel serine protease contains two ShK-domain was found from the Chinese mitten crab Eriocheir sinensis (EsShK-SP). The full-length EsShK-SP cDNA is 1927 bp and contains a 1260-bp open reading frame encoding a protein of 420 amino acids, including a signal peptide, two ShK domain, and Tryp-SPC domain. Quantitative real-time PCR showed that EsShK-SP was expressed mainly in the hemocytes, gills, intestine, and nerve, but weakly in heart, muscle, and hepatopancreas. After infected with Spiroplasma eriocheiris, the expression of EsShK-SP was significantly up-regulated from 1 d to 9 d. The Tryp-SPC domain was ligated with pGEX-4T-1 vector and prokaryotic expressed to obtain recombinant protein rSPC. When rSPC and S. eriocheiris stimulated the hemocytes of E. sinensis, the PO activity was significantly up-regulated. The subcellular localization revealed that recombinant EsShK-SP was mainly located in the cytoplasm of Drosophila S2 cells. Both absolute real-time PCR and confocal laser scanning microscope results showed that over-expression of EsShK-SP in S2 cells could decrease the copy number of S. eriocheiris. Meanwhile, the over-expression of EsShK-SP also increased the PO activity and cell viability of S2 cells. After EsShK-SP RNA interference using dsRNA, the expression levels of proPO and activity of PO decreased significantly from 48 h to 96 h. The knockdown of EsShK-SP by RNAi resulted in the copy number of S. eriocheiris in the EsShK-SP silenced group was significantly increased compared to the control groups during S. eriocheiris infection. Meanwhile, the survival rate of crabs decreased in the EsShK-SP-dsRNA group. The above results indicated that EsShK-SP plays an important immune role during E. sinensis against S. eriocheiris through regulation of the proPO system.

Spiroplasma eriocheiris Enters Drosophila Schneider 2 Cells and Relies on Clathrin-Mediated Endocytosis and Macropinocytosis

Spiroplasma eriocheiris causes great economic losses in the crustacean aquaculture industry. However, the mechanism of S. eriocheiris infecting host cells has been poorly studied. We established a Spiroplasma-infected Drosophila Schneider 2 (S2) cell model and investigated its pathogenic mechanism. First, S. eriocheiris induced S2 cell apoptosis and necrosis, seriously decreased cell viability, and increased the production of intracellular reactive oxygen species. Further research showed that S. eriocheiris can invade S2 cells, and the number of copies of intracellular spiroplasmas is sharply increased by 12 h postinfection. In addition, S. eriocheiris can cause S2 cells to form typical inclusion bodies and exhibit large vacuoles. Second, S. eriocheiris is internalized into S2 cells and strongly inhibited through blocking clathrin-mediated endocytosis using chlorpromazine and dynasore. Inhibitors of macropinocytosis, protein kinase C and myosin II, cause a significant reduction in S. eriocheiris in S2 cells. In contrast, disruption of cellular cholesterol by methyl-β-cyclodextrin and nystatin has no effect on S. eriocheiris infection. These results suggest that the entry of S. eriocheiris into S2 cells relies on clathrin-dependent endocytosis and macropinocytosis, but not via the caveola-mediated endocytic pathway. In addition, the intracellular numbers of S. eriocheiris are dramatically reduced after S2 cells are treated with cytoskeleton-depolymerizing agents, including nocodazole and cytochalasin B. Thus, cellular infection by S. eriocheiris is related to microtubules and actin filaments. This research successfully shows for the first time that S. eriocheiris can invade Drosophila S2 cells and provides a process for S. eriocheiris infection.

Spiroplasma eriocheiris Invasion Into Macrobrachium rosenbergii Hemocytes Is Mediated by Pathogen Enolase and Host Lipopolysaccharide and β-1, 3-Glucan Binding Protein

Spiroplasma eriocheiris is a crustacean pathogen, without a cell wall, that causes enormous economic loss. Macrobrachium rosenbergii hemocytes are the major targets during S. eriocheiris infection. As wall-less bacteria, S. eriocheiris, its membrane protein should interact with host membrane protein directly and firstly when invaded in host cell. In this investigation, six potential hemocyte receptor proteins were identified firstly that mediate interaction between S. eriocheiris and M. rosenbergii. Among these proteins, lipopolysaccharide and β-1, 3-glucan binding protein (MrLGBP) demonstrated to bind to S. eriocheiris using bacterial binding assays and confocal microscopy. Four spiroplasma ligand proteins for MrLGBP were isolated and identified. But, competitive assessment demonstrated that only enolase of S. eriocheiris (SeEnolase) could be a candidate ligand for MrLGBP. Subsequently, the interaction between MrLGBP and SeEnolase was confirmed by co-immunoprecipitation and co-localization in vitro. After the interaction between MrLGBP and SeEnolase was inhibited by antibody neutralization test, the virulence ability of S. eriocheiris was effectively reduced. The quantity of S. eriocheiris decreased in Drosophila S2 cells after overexpression of MrLGBP, compared with the controls. In addition, RNA interference (RNAi) knockdown of MrLGBP made M. rosenbergii more sensitive to S. eriocheiris infection. Further studies found that the immune genes, including MrLGBP and prophenoloxidase (MrproPO), MrRab7A, and Mrintegrin α1 were significantly up-regulated by SeEnolase stimulation. After SeEnolase pre-stimulation, the ability of M. rosenbergii resistance to S. eriocheiris was significantly improved. Collectively, this investigation demonstrated that MrLGBP and pathogen SeEnolase involved in mediating S. eriocheiris invasion into M. rosenbergii hemocytes.

Characterization of cathepsin D from Eriocheir sinensis involved in Spiroplasma eriocheiris infection

Cathepsin D (catD) belongs to a lysosomal aspartic protease superfamily. The full-length catD cDNA from the Chinese mitten crab Eriocheir sinensis (EscatD) was 2748 bp and contained a 1158-bp ORF encoding a protein of 385 amino acids, including a signal peptide and two N-glycosylation sites. Phylogenetic analysis showed that EscatD was clustered into a single group, together with other catD for crustaceans. Quantitative real-time PCR revealed that EscatD was expressed mainly in the eyes, hemocytes, intestine and nerve and was expressed weakly in heart, muscle and gills. After challenge with Spiroplasma eriocheiris, the expression of EscatD was significantly up-regulated from 1 d to 9 d. The copy number of S. eriocheiris in a silencing EscatD group was significantly higher than those in the control groups during S. eriocheiris infection. Meanwhile, the survival rate of crabs decreased in an EscatD-dsRNA group. We further found that knockdown of EscatD by RNA interference resulted in a downward trend of expression levels of JNK, ERK, relish and p38 during the early stage, as well as a reduction in the expression of five antimicrobial peptides genes, namely, crusrin1, crustin2, ALF1, ALF2 and ALF3. The subcellular localization experiment suggested that recombinant EscatD was mainly located in the cytoplasm. The over-expression in Drosophila S2 cells indicated that EscatD could decrease the copy number of S. eriocheiris and increase cell viability. The above results demonstrated that EscatD plays an important immune role in E. sinensis to S. eriocheiris challenge.

The function of Eriocheir sinensis transferrin and iron in Spiroplasma eriocheiris infection

Transferrin, a member of the iron binding superfamily protein, plays an extremely important role in the transport of iron in the biological process of cells. The result of preliminary proteomic study on E. sinensis hemocytes infected Spiroplasma eriocheiris showed the expression of transferrin (EsTF) and ferrin (EsFe) significantly changed. In addition, other reports have confirmed that transferrin, ferritin and iron are involved in the immune response of hosts. In order to validate the immune function of EsTF, the whole length of EsTF was successfully amplified by the gene cloning and RACE technique. The results showed that the full-length cDNA of the EsTF gene was 2748 bp, including a 2193 bp open reading frame which encodes 730 amino acids. The result of bioinformatics analysis showed EsTF contains two highly conserved TR_FER domains. Evolutionary analysis showed that EsTF has a close genetic relationship with other TFs of invertebrates. In addition, EsTF mRNA was highly transcripted in nerve and intestine tissues, followed by hemocytes. The expression of EsTF, EsFe1 and EsFe2 increased after exogenous supplemental of iron under the concentration of 100 nmol/L in water. After exogenous supplement of iron and injection with S. eriocheiris, these three gene transcription of mRNA levels were higher than that of PBS group, while lower than the S. eriocheiris group and the iron group. Besides, the copy number of S. eriocheiris in the experimental group was significantly reduced, and the death rate decreased. As can be seen, iron made transferrin and ferritin return to normal levels during the infection of S. eriocheiris and help the host maintain normal immunity levels to resist S. eriocheiris. These results further demonstrated that EsTF, EsFe1, EsFe2 and iron play a role in the immune defense mechanism of the crabs to resist S. eriocheiris infection.

The function of serpin-2 from Eriocheir sinensis in Spiroplasma eriocheiris infection

Serpin families classified serine protease inhibitors regulate various physiological processes. However, there is not study on the role of serpin in immune responses against Spiroplasma eriocheiris as a novel causative pathogen in the Chinese mitten crab, Eriocheir sinensis. In our study, quantitative real-time PCR (qRT-PCR) revealed that the mRNA transcripts of Esserpin-2 were ubiquitous in every tissue, relative higher expression in hepatopancreas, gill and hemocytes, while the intestine, muscle, heart and nerve showed relative lower expression. Followed by infection with S. eriocheiris, the transcripts of Esserpin-2 were significantly down-regulated from 1 d to 7 d. After double-stranded RNA injection, the transcripts of Esserpin-2 dramatically declined from 48 h to 96 h. The transcripts of proPO were found to be obviously increased after Esserpin-2 silenced, meanwhile, LGBP with no significant difference. The copy number of S. eriocheiris and subsequently the mortality of crabs in a silencing Esserpin-2 group were significantly less than control groups during infection. The subcellular localization experiment suggested that recombinant Esserpin-2 was mainly located in the cytoplasm. Finally, over-expression assay in Drosophila S2 cells indicated that Esserpin-2 could increase copies of S. eriocheiris and result in cell death. These findings demonstrated that Esserpin-2 involved in the innate immune mechanism of E. sinensis in response to S. eriocheiris infection.

Evolution and Diversity of Inherited Spiroplasma Symbionts in Myrmica Ants

Microbial partners play important roles in the biology and ecology of animals. In insects, maternally transmitted symbionts are especially common and can have host effects ranging from reproductive manipulation to nutrient provisioning and defense against natural enemies. In this study, we report a genus-wide association of Myrmica ants with the inherited bacterial symbiont Spiroplasma We screen Myrmica ants collected from the wild, including the invasive European fire ant, Myrmica rubra, and find an extraordinarily high prevalence of this symbiont-8 of 9 species, 42 of 43 colonies, and 250 of 276 individual workers harbored Spiroplasma-only one host species was uninfected. In our screens, each host species carried a distinct Spiroplasma strain, and none were infected with more than one strain. All symbionts belong to the citri clade, allied most closely with pathogenic strains of Spiroplasma infecting corn crops and honeybees, and there is strong evidence of host-symbiont persistence across evolutionary time scales. Genome sequencing of two Spiroplasma symbionts revealed candidate genes that may play a part in the symbiosis, a nutrient transporter absent from other Spiroplasma strains, and a ribosome-inactivating protein previously implicated in parasite defense. These results together suggest long-term, likely mutualistic, relationships atypical of Spiroplasma-insect associations with potential significance for broad ecological interactions with MyrmicaIMPORTANCE Animal-associated microbial symbionts can dramatically affect the biology of their hosts. The identification and characterization of these intimate partnerships remain an essential component of describing and predicting species interactions, especially for invasive host species. Ants perform crucial ecological functions as ecosystem engineers, scavengers, and predators, and ants in the genus Myrmica can be aggressive resource competitors and reach high densities in their native and invaded habitats. In this study, a novel symbiosis is identified between Myrmica ants and the facultative bacterial symbiont Spiroplasma Broad host distribution, high frequencies of infection, and host-symbiont codivergence over evolutionary time scales, an uncommon feature of Spiroplasma associations, suggest an important likely mutualistic interaction. Genome sequencing identified highly divergent gene candidates that may contribute to Spiroplasma's role as a possible defensive or nutritional partner in Myrmica.

An integrated metabolic consequence of Hepatospora eriocheir infection in the Chinese mitten crab Eriocheir sinensis

Despite the economic and evolutionary importance of aquatic host-infecting microsporidian species, at present, limited information has been provided about the microsporidia-host interactions. This study focused on Hepatospora eriocheir, an emerging microsporidian pathogen for the Chinese mitten crab Eriocheir sinensis. Hypertrophy of hepatopancreas cells was a common feature of H. eriocheir infection. More importantly, mitochondria of the hepatopancreas were drawn around the H. eriocheir, most likely to aid the uptake of ATP directly from the host. To better understand the crab anti-microsporidian response, de novo transcriptome sequencing of the hepatopancreas tissue was furtherly proceeded. A total of 47.84 M and 57.21 M clean reads were generated from the hepatopancreas of H. eriocheir infected and control groups respectively. Based on homology searches, functional annotation with 6 databases (Nr, Swiss-Prot, KEGG, KOGs, Pfam and GO) for 88,168 unigenes was performed. 2619 genes were identified as differently up-regulated and 2541 genes as differently down-regulated. Prominent functional categories enriched with differentially expressed genes (DEGs) were "ATP binding", "mitochondrion and extracellular region", "oxygen transporter activity", "oxidoreductase activity", "alanine, aspartate and glutamate metabolism", "carbohydrate metabolic process", "starch and sucrose metabolism" and "fatty acid biosynthesis". These results confirmed a parasite external energy supply and an integrated metabolic stress. In addition, simple sequence repeats (SSRs) and single nucleotide polymorphisms (SNPs) were also identified from the gene library. Taken together, these findings allow us to better understand the underlying mechanisms regulating interactions between H. eriocheir and the crab E. sinensis.

Identification and function analysis of ras-related nuclear protein from Macrobrachium rosenbergii involved in Spiroplasma eriocheiris infection

A ras-related nuclear protein (Ran) protein was obtained from Macrobrachium rosenbergii, named MrRan. Phylogenetic analysis results showed that MrRan was clustered in one group together with other crustaceans. Tissue distribution analysis revealed that MrRan was expressed mainly in gill, intestine and stomach, and expressed weakly in muscle. The MrRan expression levels in gill and hemocyte of prawns were significantly up-regulated after challenged by Spiroplasma eriocheiris. The copy number of S. eriocheiris in MrRan dsRNA injection group was significantly less than control groups during infection. Meanwhile, silencing MrRan obviously increased the survival rate of prawns. The subcellular localization experiment suggested that recombinant MrRan was mainly located in the nucleus, and relatively weak in the cytoplasm. Finally, over-expression in Drosophila S2 cell indicated that MrRan could increase copies of S. eriocheiris and decrease of cell viability. The present study suggested that MrRan participated in regulating the phagocytosis of S. eriocheiris in M. rosenbergii.

Changes in the gut microbiome of the Chinese mitten crab (Eriocheir sinensis) in response to White spot syndrome virus (WSSV) infection

Intestinal microorganisms play important roles in maintaining host health, but their functions in aquatic animal hosts have yet to be fully elucidated. The Chinese mitten crab, Eriocheir sinensis, is one such example. We attempted to identify the shift of gut microbiota that occurred in response to infection of white spot syndrome virus (WSSV), an emerging viral pathogen in the crab aquaculture industry. The microbiota may exert some control over aspects of the viral pathogenesis. We investigated the changes in composition and structure of the crab gut microbiome during various WSSV infection stages of 6 h post-infection (hpi) and 48 hpi, using a 16S rRNA approach on the MiSeq Illumina sequencing platform. Four phyla (Firmicutes, Proteobacteria, Tenericutes and Bacteroidetes) were most dominant in the gut of E. sinensis regardless of the WSSV infection stages. However, further analysis revealed that over 12 bacterial phyla, 44 orders and 68 families were significantly different in abundance at various states of WSSV infection. Several intriguing aspects of E. sinensis gut bacteria that had not been previously reported were also uncovered, such as class Mollicutes was dominant here, but absent in crabs from Yangtze River estuary and Chongming Islands. Overall, this study provided the first evidence that changes in gut microbiome were closely associated with the severity of WSSV infection and that indicator taxa could be used to evaluate the crab health status.

Interaction of heat shock protein 60 (HSP60) with microRNA in Chinese mitten crab during Spiroplasma eriocheiris infection

Heat shock protein 60 from the Chinese mitten crab Eriocheir sinensis (EsHSP60) was previously identified in relation to Spiroplasma eriocheiris infection by isobaric tags for relative and absolute quantitation labelling followed by liquid chromatography-tandem mass spectrometry. In the present study, to validate the immune function of this protein, the cDNA of the EsHSP60 gene was cloned. Various crab tissues were assessed using real-time PCR, which showed that EsHSP60 transcription occurred in all tissues examined. The expression profiles of EsHSP60 in haemolymph at transcription and protein levels when infected with S. eriocheiris were investigated by real-time PCR and Western blot analysis, respectively. A significant increase of EsHSP60 transcription and protein expression appeared post-injection in response to S. eriocheiris infection when compared to the control group. The double-luciferase reporter gene assay showed that the microRNA PC-533-3p interacted with the 3'-untranslated region of EsHSP60 and inhibited the translation of EsHSP60. The expression profiles of PC-533-3p during S. eriocheiris infection were also investigated by real-time PCR. However, the change tendency of PC-533-3p was opposite to that of the EsHSP60 after S. eriocheiris challenge. These data indicate that the EsHSP60 proteins may play an important role in mediating the immune responses of E. sinensis to an S. eriocheiris challenge.

Generality of toxins in defensive symbiosis: Ribosome-inactivating proteins and defense against parasitic wasps in Drosophila

While it has become increasingly clear that multicellular organisms often harbor microbial symbionts that protect their hosts against natural enemies, the mechanistic underpinnings underlying most defensive symbioses are largely unknown. Spiroplasma bacteria are widespread associates of terrestrial arthropods, and include strains that protect diverse Drosophila flies against parasitic wasps and nematodes. Recent work implicated a ribosome-inactivating protein (RIP) encoded by Spiroplasma, and related to Shiga-like toxins in enterohemorrhagic Escherichia coli, in defense against a virulent parasitic nematode in the woodland fly, Drosophila neotestacea. Here we test the generality of RIP-mediated protection by examining whether Spiroplasma RIPs also play a role in wasp protection, in D. melanogaster and D. neotestacea. We find strong evidence for a major role of RIPs, with ribosomal RNA (rRNA) from the larval endoparasitic wasps, Leptopilina heterotoma and Leptopilina boulardi, exhibiting the hallmarks of RIP activity. In Spiroplasma-containing hosts, parasitic wasp ribosomes show abundant site-specific depurination in the α-sarcin/ricin loop of the 28S rRNA, with depurination occurring soon after wasp eggs hatch inside fly larvae. Interestingly, we found that the pupal ectoparasitic wasp, Pachycrepoideus vindemmiae, escapes protection by Spiroplasma, and its ribosomes do not show high levels of depurination. We also show that fly ribosomes show little evidence of targeting by RIPs. Finally, we find that the genome of D. neotestacea's defensive Spiroplasma encodes a diverse repertoire of RIP genes, which are differ in abundance. This work suggests that specificity of defensive symbionts against different natural enemies may be driven by the evolution of toxin repertoires, and that toxin diversity may play a role in shaping host-symbiont-enemy interactions.

Direct visualization of the novel pathogen, Spiroplasma eriocheiris, in the freshwater crayfish Procambarus clarkii (Girard) using fluorescence in situ hybridization

Spiroplasma eriocheiris is the first spiroplasma strain known to be pathogenic to freshwater crustaceans. It has caused considerable economic losses both in the freshwater crayfish Procambarus clarkii (Girard) and in some other crustaceans. The monitoring of the pathogen in crustacean populations and study of its behaviour in the laboratory require the development of reliable diagnostic tools. In this article, we improved microscopic identification of S. eriocheiris by combining in situ hybridization with specific fluorescently labelled oligonucleotide probes. The established fluorescence in situ hybridization (FISH) allowed simultaneous visualization, identification and localization of S. eriocheiris in the tissues of diseased crayfish P. clarkii and exhibited low background autofluorescence and ideal signal-to-noise ratio. With the advantages of better tissue penetration, potentially more specific and stable, we designed three species-specific oligonucleotide probes utilizing the sequences of 16S-23S rRNA intergenic spacer regions (ISRs) of S. eriocheiris. Positive hybridization signals were visualized in haemocytes and connective tissues of hepatopancreas, cardiac muscle and gill from diseased crayfish. This unique distribution pattern matched the pathological changes when diagnosed by H&E staining and indicated that S. eriocheiris probably spread throughout the tissues in P. clarkii by hemokinesis. This assay will facilitate our understanding of the pathogenesis of S. eriocheiris and enhance the early diagnosis of the novel pathogen.

iTRAQ-based proteomic study of the effects of Spiroplasma eriocheiris on Chinese mitten crab Eriocheir sinensis hemocytes

Spiroplasma eriocheiris is as a novel pathogen of Chinese mitten crab Eriocheir sinensis tremor disease. The hemocytes have been shown to be major target cells in S. eriocheiris infection. The aim of this study was to examine the hemocytes' immune response at the protein levels. The differential proteomes of the crab hemocytes were analyzed immediately prior to injection with the pathogen, and at 10 d post-injection by isobaric tags for relative and absolute quantization (iTRAQ) labeling, followed by liquid chromatography-tandem mass spectrometry (LC-MS/MS). A total of 1075 proteins were identified by LC-MS/MS and de novo sequencing data. Using a 1.2-fold change in expression as a physiologically significant benchmark, 76 differentially expressed proteins (7.07%) were reliably quantified by iTRAQ analysis. Thirty-five (3.26%) proteins were up-regulated and 41 (3.81%) proteins were down-regulated resulting from a S. eriocheiris infection. Approximately 20 differential proteins in hemocytes were involved in the stress and immune responses. Up-regulated proteins included alpha-2-macroglobulin (α2M), prostaglandin D synthase (GST), ferritin, and heat shock protein 60. Down-regulated proteins included two lectins (mannose-binding protein and hemocytin), three kinds of serine proteinase inhibitors (two serpins and pacifastin), three different kinds of serine proteases, mitogen-activated protein kinase kinase (MAPKK), and two thioredoxins (Trx), crustin, etc. Selected bioactive factors (α2M, GST, ferritin, tubulin, crustin, thioredoxin, clip domain serine protease and serpin) are verified by their immune roles in the S. eriocheiris infection using Real-time PCR. The variation trend of immune gene's mRNA expression is similar with the result of iTRAQ, except the tubulin. The prophenoloxidase-activating system, antimicrobial action and antioxidant system involved in the immune responses of E. sinensis is believed to be a resistance to S. eriocheiris infection. This is the first report of the proteome response of crab hemocytes against S. eriocheiris infection. These findings contribute to our understanding of tremor disease processes in crabs, and provide the first evidence to promote a search for potential biomarkers of the disease.