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- Identification and Characterization of HEPN‑MNT Type II TA System from Methanothermobacter thermautotrophicus ΔH
- Wonho Choi , Anoth Maharjan , Hae Gang Im , Ji-Young Park , Jong-Tae Park , Jung-Ho Park
- J. Microbiol. 2023;61(4):411-421. Published online April 18, 2023
- DOI: https://doi.org/10.1007/s12275-023-00041-9
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Abstract
- Toxin-antitoxin (TA) systems are widespread in bacteria and archaea plasmids and genomes to regulate DNA replication, gene transcr!ption, or protein translation. Higher eukaryotic and prokaryotic nucleotide-binding (HEPN) and minimal nucleotidyltransferase (MNT) domains are prevalent in prokaryotic genomes and constitute TA pairs. However, three gene pairs (MTH304/305, 408/409, and 463/464) of Methanothermobacter thermautotropicus ΔH HEPN-MNT family have not been studied as TA systems. Among these candidates, our study characterizes the MTH463/MTH464 TA system. MTH463 expression inhibited Escherichia coli growth, whereas MTH464 did not and blocked MTH463 instead. Using site-directed MTH463 mutagenesis, we determined that amino acids R99G, H104A, and Y106A from the R[ɸX]4-6H motif are involved with MTH463 cell toxicity. Furthermore, we established that purified MTH463 could degrade MS2 phage RNA, whereas purified MTH464 neutralized MTH463 activity in vitro. Our results indicate that the endonuclease toxin MTH463 (encoding a HEPN domain) and its cognate antitoxin MTH464 (encoding the MNT domain) may act as a type II TA system in M. thermautotropicus ΔH. This study provides initial and essential information studying TA system functions, primarily archaea HEPN-MNT family.
Research Support, Non-U.S. Gov't
- Antiviral Activities of Flavonoids Isolated from the Bark of Rhus verniciflua Stokes against Fish Pathogenic Viruses In Vitro
- So Young Kang , Ji-Young Kang , Myung-Joo Oh
- J. Microbiol. 2012;50(2):293-300. Published online April 27, 2012
- DOI: https://doi.org/10.1007/s12275-012-2068-7
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- 91 Citations
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Abstract
- An 80% methanolic extract of Rhus verniciflua Stokes bark showed significant anti-viral activity against fish pathogenic infectious hematopoietic necrosis virus (IHNV) and viral hemorrhagic septicemia virus (VHSV) in a cell-based assay measuring virus-induced cytopathic effect (CPE). Activity-guided fractionation and isolation for the 80% methanolic extract of R. verniciflua yielded the most active ethyl acetate fraction, and methyl gallate (1) and four flavonoids: fustin (2), fisetin (3), butin (4) and sulfuretin (5). Among them, fisetin (3) exhibited high antiviral activities against both IHNV and VHSV showing EC50 values of 27.1 and 33.3 μM with selective indices (SI = CC50/EC50) more than 15, respectively. Fustin (2) and sulfuretin (5) displayed significant antiviral activities showing EC50 values of 91.2– 197.3 μM against IHNV and VHSV. In addition, the antiviral activity of fisetin against IHNV and VHSV occurred up to 5 hr post-infection and was not associated with direct virucidal effects in a timed addition study using a plaque reduction assay. These results suggested that the bark of R. verniciflua and isolated flavonoids have significant anti-viral activity against IHNV and VHSV, and also have potential to be used as anti-viral therapeutics against fish viral diseases.
Research Support, U.S. Gov't, Non-P.H.S.
- Shedding of Viral Hemorrhagic Septicemia Virus (Genotype IVb) by Experimentally Infected Muskellunge (Esox masquinongy)
- Robert K. Kim , Mohamed Faisal
- J. Microbiol. 2012;50(2):278-284. Published online April 27, 2012
- DOI: https://doi.org/10.1007/s12275-012-1145-2
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- 26 Citations
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Abstract
- Previous experimental infection demonstrated that juvenile muskellunge (Esox masquinongy) can survive experimental infection of viral hemorrhagic septicemia virus, Genotype IVb (VHSV IVb) at a low concentration of exposure. Herein we report that survivors of experimental infection with VHSV IVb shed the virus into the surrounding environment for an extended period of time. When muskellunge were exposed to VHSV IVb by immersion at a concentration of 1,400 plaque forming units (PFU)/ml, VHSV IVb was detected in the water of surviving fish for up to 15 weeks postexposure (p.e.) with the highest levels of shedding occurring between weeks 1 and 5 p.e. We estimated that each juvenile muskellunge can shed upwards of 1.36×105 PFU/fish/h after initial exposure signifying the uptake and amplification of VHSV to several orders of magnitude above the original exposure concentration. Muskellunge surviving low concentration exposure were re-infected with VHSV IVb by immersion at week 22 p.e. at concentrations ranging from 0 to 106 PFU/ml. Viral shedding was detected in all re-exposed fish, including mock rechallenged controls up to 15 consecutive weeks. Rates of viral shedding were substantially higher following rechallenge in the first 5 weeks. The highest rate of viral shedding was approximately 4.6×106 PFU/fish/h and shedding did not necessarily correspond to the re-exposure VHSV concentration. The results of this study shed new light into the dynamics of VHSV IVb shedding in a highly susceptible host and provide useful insights to fishery managers to design effective control strategies to this deadly virus.
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