The adsorption mechanisms of algae-bacteria symbiotic system and its fast formation process.

The formation process of the algae-bacteria symbiotic system (ABSS) was analyzed, and the formation adsorption conditions were optimized. The role of extracellular polymeric substances (EPS), specific surface area and zeta potential in adsorption mechanisms were assessed and proposed. The results showed the dry weight of the ABSS and adsorption efficiency of microalgae reached the highest under the conditions of 25 °C, pH 6.0, 160 rpm and CaCl2 2.0 mg/mL. The process of the ABSS formation could be mainly divided into the fast stage and slow stage. The roles of EPS, specific surface area and zeta potential accounted for 84.22%, 5.17% and 10.61% of the adsorption capacity, respectively. EPS dominated the formation of the ABSS. The results indicated that mycelial pellets were biosorption materials and had the characteristics of chemical materials.

Zebrafish NIK Mediates IFN Induction by Regulating Activation of IRF3 and NF-κB.

Type I IFN mediates the innate immune system to provide defense against viral infections. NF-κB-inducing kinase (NIK) potentiates the basal activation of endogenous STING, which facilitates the recruitment of TBK1 with the ectopically expressed IRF3 to induce IFN production. Moreover, NIK phosphorylates IKKα and confers its ability to phosphorylate p100 (also known as NF-κB2) in mammals. Our study demonstrated that NIK plays a critical role in IFN production in teleost fish. It was found that NIK interacts with IKKα in the cytoplasm and that IKKα phosphorylates the NIK at the residue Thr432, which is different from the mammals. Overexpression of NIK caused the activation of IRF3 and NF-κB, which in turn led to the production of IFN and IFN-stimulated genes (ISGs). Furthermore, the ectopic expression of NIK was observed to be associated with a reduced replication of the fish virus, whereas silencing of endogenous NIK had an opposite effect in vitro. Furthermore, NIK knockdown significantly reduced the expression of IFN and key ISGs in zebrafish larvae after spring viremia of carp virus infection. Additionally, the replication of spring viremia of carp virus was enhanced in NIK knockdown zebrafish larvae, leading to a lower survival rate. In summary, our findings revealed a previously undescribed function of NIK in activating IFN and ISGs as a host antiviral response. These findings may facilitate the establishment of antiviral therapy to combat fish viruses.

Identification of fish CMPK2 as an interferon stimulated gene against SVCV infection.

Cytidine/uridine monophosphate kinase 2 (CMPK2) is known as a nucleoside monophosphate kinase in mitochondria to maintains intracellular UTP/CTP, and could be induced by immunostimulants LPS and Poly (I:C) in mammals, suggesting its potential antiviral and antibacterial role. In this study, CMPK2 was cloned and characterized in Fathead minnow (FHM) cells. In vivo analysis of tissue distribution revealed that CMPK2 transcript was detected in all the tissues of zebrafish (Danio rerio) examined in this study, particularly abundant in liver, spleen and kidney. In addition, indirect immunofluorescence showed that CMPK2 was localized in the cytoplasm of FHM cells. Expression of CMPK2 mRNA was significantly up-regulated following challenge with Spring viraemia of carp virus (SVCV), poly(I:C), or zebrafish IFN1 and IFN3 both in vitro and in vivo. Furthermore, overexpression and RNA interference of CMPK2 in SVCV-infected FHM cells showed significantly antiviral effect. In summary, this study for the first time shows the presence and distribution of CMPK2 in different tissues of zebrafish, but also demonstrates its antiviral potential against SVCV infection in vivo. These new findings could contribute to explain the molecular mechanism of the CMPK2 mediated antiviral function.

Molecular Characterization and Expression Analysis of ftr01, ftr42, and ftr58 in Zebrafish (Danio rerio).

Tripartite motif (TRIM) proteins were shown to play an important role in innate antiviral immunity. FinTRIM (ftr) is a new subset of TRIM genes that do not possess obvious orthologs in higher vertebrates. However, little is known about its function. In this study, we used bioinformatic analysis to examine the phylogenetic relationships and conserved domains of zebrafish (Danio rerio) ftr01, ftr42, and ftr58, as well as qualitative real-time PCR to examine their expression patterns in zebrafish embryonic fibroblast (ZF4) cells and zebrafish tissues. Sequence analysis showed that the three finTRIMs are highly conserved, and all contain a RING domain, B-box domain, and SPRY-PRY domain. In addition, ftr42 and ftr58 had one coiled-coil domain (CCD), whereas ftr01 had two CCDs. Tissue expression analysis revealed that the mRNA level of ftr01 was the highest in the liver, whereas those of ftr42 and ftr58 were the highest in the gill; the expression of these finTRIMs was clearly upregulated not in the eyes, but in the liver, spleen, kidney, gill, and brain of zebrafish following spring viremia of carp virus (SVCV) infection. Similarly, the expression of these three finTRIM genes also increased in ZF4 cells after SVCV infection. Our study revealed that ftr01, ftr42, and ftr58 may play an important role in antiviral immune responses, and these findings validate the need for more in-depth research on the finTRIM family in the future.

The antiviral mechanism of viperin and its splice variant in spring viremia of carp virus infected fathead minnow cells.

Viperin is known to play an important role in innate immune and its antiviral mechanisms are well demonstrated in mammals. Fish Viperin mediates antiviral activity against several viruses. However, little has been done to the underlying mechanism. Here, we discovered a novel Viperin splice variant named Viperin_sv1 from viral-infected FHM cells. Spring varimia of carp virus (SVCV) was able to increase the mRNA levels of both Viperin and Viperin_sv1, while poly(I:C) only has effect on Viperin. Viperin functions as an antiviral protein at 24 h post-SVCV infection, but the antiviral activity dramatically declined at late infection stages. However, Viperin_sv1 inhibited SVCV replication significantly at all the tested time. Viperin_sv1, but not Viperin can facilitate the production of type I IFN and IFN stimulate genes (ISGs) through activation of RIG-1, IRF3 and IRF7 signaling cascades. On the other hand, SVCV down-regulated Viperin_sv1 at the protein level through the proteasome pathway to keep itself away from the immune system monitoring. Taken together, these findings provide new insights into the regulation of Viperin from the posttranscriptional modification perspective and the role of splicing variant Viperin_sv1 in virus-host interaction.

Fish-specific finTRIM FTR36 triggers IFN pathway and mediates inhibition of viral replication.

The tripartite motif (TRIM) family involves many cellular processes, including fundamental functions in antiviral immunity. Antiviral activities of TRIMs are reported in a variety of patterns, and one of the most significant channels is related to the activation of the type-I interferon (IFN) pathway. In this study, we described a fintrim (ftr) gene named ftr36, which is mainly expressed in the gills, skin, and intestines. This study shows that ftr36 encodes a protein affording a potent antiviral effect. In vitro, overexpression of FTR36 mediated an upregulated pattern of recognition receptor retinoic acid-inducible gene I (RIG-I), interferon regulatory factor 3/7(IRF3/7), IFN, and IFN-stimulated genes (ISGs) expression. Thereby, FTR36 expression could afford host defense against the spring viremia of carp virus (SVCV) and the giant salamander iridovirus (GSIV). With the deletion of the RING domain or B30.2 domain separately, the antiviral ability of FTR36 was abolished partially and almost lost its ability to activate the IFN-pathway. These findings indicate that both RING and B30.2 domains are indispensable for the antiviral activity of FTR36. Altogether, this study described a finTRIM FTR36, which can activate IFN-pathways and stimulate ISGs to provide host defense against viral infections.