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Naturally occurring substitution in one amino acid in VHSV phosphoprotein enhances viral virulence in flounder.

ABSTRACT: Viral hemorrhagic septicemia virus (VHSV) is a rhabdovirus that causes high mortality in cultured flounder. Naturally occurring VHSV strains vary greatly in virulence. Until now, little has been known about genetic alterations that affect the virulence of VHSV in flounder. We recently reported the full-genome sequences of 18 VHSV strains. In this study, we determined the virulence of these 18 VHSV strains in flounder and then the assessed relationships between differences in the amino acid sequences of the 18 VHSV strains and their virulence to flounder. We identified one amino acid substitution in the phosphoprotein (P) (Pro55-to-Leu substitution in the P protein; PP55L) that is specific to highly virulent strains. This PP55L substitution was maintained stably after 30 cell passages. To investigate the effects of the PP55L substitution on VHSV virulence in flounder, we generated a recombinant VHSV carrying PP55L (rVHSV-P) from rVHSV carrying P55 in the P protein (rVHSV-wild). The rVHSV-P produced high level of viral RNA in cells and showed increased growth in cultured cells and virulence in flounder compared to the rVHSV-wild. In addition, rVHSV-P significantly inhibited the induction of the IFN1 gene in both cells and fish at 6 h post-infection. An RNA-seq analysis confirmed that rVHSV-P infection blocked the induction of several IFN-related genes in virus-infected cells at 6 h post-infection compared to rVHSV-wild. Ectopic expression of PP55L protein resulted in a decrease in IFN induction and an increase in viral RNA synthesis in rVHSV-wild-infected cells. Taken together, our results are the first to identify that the P55L substitution in the P protein enhances VHSV virulence in flounder. The data from this study add to the knowledge of VHSV virulence in flounder and could benefit VHSV surveillance efforts and the generation of a VHSV vaccine.

SUBMITTER: Hwang JY

PROVIDER: S-EPMC7845975 | biostudies-literature | 2021 Jan

REPOSITORIES: biostudies-literature

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Naturally occurring substitution in one amino acid in VHSV phosphoprotein enhances viral virulence in flounder.

Hwang Jee Youn JY Lee Unn Hwa UH Heo Min Jin MJ Kim Min Sun MS Jeong Ji Min JM Kim So Yeon SY Kwon Mun Gyeong MG Jee Bo Young BY Kim Ki Hong KH Park Chan-Il CI Park Jeong Woo JW

PLoS pathogens 20210119 1

Viral hemorrhagic septicemia virus (VHSV) is a rhabdovirus that causes high mortality in cultured flounder. Naturally occurring VHSV strains vary greatly in virulence. Until now, little has been known about genetic alterations that affect the virulence of VHSV in flounder. We recently reported the full-genome sequences of 18 VHSV strains. In this study, we determined the virulence of these 18 VHSV strains in flounder and then the assessed relationships between differences in the amino acid seque ...[more]

PMID: 33465148

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Project description:Virulence, the degree to which a pathogen harms its host, is an important but poorly understood aspect of host-pathogen interactions. Virulence is not static, instead depending on ecological context and potentially evolving rapidly. For instance, at the start of an epidemic, when susceptible hosts are plentiful, pathogens may evolve increased virulence if this maximizes their intrinsic growth rate. However, if host density declines during an epidemic, theory predicts evolution of reduced virulence. Although well-studied theoretically, there is still little empirical evidence for virulence evolution in epidemics, especially in natural settings with native host and pathogen species. Here, we used a combination of field observations and lab assays in the Daphnia-Pasteuria model system to look for evidence of virulence evolution in nature. We monitored a large, naturally occurring outbreak of Pasteuria ramosa in Daphnia dentifera, where infection prevalence peaked at ~ 40% of the population infected and host density declined precipitously during the outbreak. In controlled infections in the lab, lifespan and reproduction of infected hosts was lower than that of unexposed control hosts and of hosts that were exposed but not infected. We did not detect any significant changes in host resistance or parasite infectivity, nor did we find evidence for shifts in parasite virulence (quantified by host lifespan and number of clutches produced by hosts). However, over the epidemic, the parasite evolved to produce significantly fewer spores in infected hosts. While this finding was unexpected, it might reflect previously quantified tradeoffs: parasites in high mortality (e.g., high predation) environments shift from vegetative growth to spore production sooner in infections, reducing spore yield. Future studies that track evolution of parasite spore yield in more populations, and that link those changes with genetic changes and with predation rates, will yield better insight into the drivers of parasite evolution in the wild.Supplementary informationThe online version contains supplementary material available at 10.1007/s10682-022-10169-6.

Project description:BackgroundMutations in the PB1 subunit of RNA-dependent RNA polymerase (RdRp) of influenza A virus can affect replication fidelity. Before the influenza A/H1N1 pandemic in 2009, most human influenza A/H1N1 viruses contained the avian-associated residue, serine, at position 216 in PB1. However, near the onset of the 2009 pandemic, human viruses began to acquire the mammalian-associated residue, glycine, at PB1-216, and PB1-216G became predominant in human viruses thereafter.MethodsUsing entropy-based analysis algorithm, we have previously identified several host-specific amino-acid signatures that separated avian and swine viruses from human influenza viruses. The presence of these host-specific signatures in human influenza A/H1N1 viruses suggested that these mutations were the result of adaptive genetic evolution that enabled these influenza viruses to circumvent host barriers, which resulted in cross-species transmission. We investigated the biological impact of this natural avian-to-mammalian signature substitution at PB1-216 in human influenza A/H1N1 viruses.ResultsWe found that PB1-216G viruses had greater mutation potential, and were more sensitive to ribavirin than PB1-216S viruses. In oseltamivir-treated HEK293 cells, PB1-216G viruses generated mutations in viral neuraminidase at a higher rate than PB1-216S viruses. By contrast, PB1-216S viruses were more virulent in mice than PB1-216G viruses. These results suggest that the PB1-S216G substitution enhances viral epidemiological fitness by increasing the frequency of adaptive mutations in human influenza A/H1N1 viruses.ConclusionsOur results thus suggest that the increased adaptability and epidemiological fitness of naturally arising human PB1-216G viruses, which have a canonical low-fidelity replicase, were the biological mechanisms underlying the replacement of PB1-216S viruses with a high-fidelity replicase following the emergence of pdmH1N1. We think that continued surveillance of such naturally occurring PB1-216 variants among others is warranted to assess the potential impact of changes in RdRp fidelity on the adaptability and epidemiological fitness of human A/H1N1 influenza viruses.

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Naturally occurring substitution in one amino acid in VHSV phosphoprotein enhances viral virulence in flounder.

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Naturally occurring substitution in one amino acid in VHSV phosphoprotein enhances viral virulence in flounder.

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