Proteolytic cleavages play an important role in reovirus infection during entry into cells. The effects of protease digestion on the morphology, infectivity and polypeptide composition of grass carp reovirus (GCRV) were investigated. Following treatment with chymotrypsin, the different subviral particles of GCRV were isolated using density gradient centrifugation and examined by electron microscope (EM). Analysis of protein components revealed that the viral outer capsid was composed of VP5 and VP7. Of particular note, VP5 was found to primarily exist within virions as cleaved fragments, which was consistent with observations for its analogue mu1/mu1C, generated by autolysis of mu1 at the mu1N/mu1C junction for mammalian orthoreoviruses (MRVs). Meanwhile, both trypsin- and chymotrypsin-treated GCRV particles appeared to have an enhanced infectivity. Moreover, the corresponding assays between infectivity and protein component indicated that the enhancement of infectivity was correlated to the complete digestion of the outer capsid protein VP7 and partial cleavage of VP5. Overall, the results presented in this paper provided strong evidence that the proteins VP5 and VP7 of GCRV play an indispensable role in viral infection.

The increasing use of silver (Ag) and titanium dioxide (TiO2) nanoparticles (NPs) in consumer products and their inevitable seepage into the environment prompted us to investigate their potential toxicity to a fish cell line (BF-2) and zebrafish embryos under dark and Simulated Solar Light (SSL) exposure conditions. Using high throughput screening (HTS) platforms, we showed that the oxidative stress-dependent cytotoxicity and embryonic toxicity of NPs were significantly increased upon exposure to SSL. While, the toxicity of TiO2 NPs under SSL exposure could be explained by hydroxyl radical generation, the enhanced toxicity of Ag NPs under SSL exposure was due to surface oxidation and physicochemical modification of Ag NPs and shedding of Ag+, leading to an increased bioavailability of silver. Our observations that solar light could induce physicochemical transformation of TiO2 and Ag NPs and enhance their toxic potential emphasizes the need for conducting future toxicity studies under environmentally relevant exposure conditions to guide decision making on the safe handling of NPs.

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