Polymerase Fidelity Contributes to Foot-and-Mouth Disease Virus Pathogenicity and Transmissibility In Vivo.

The low fidelity of foot-and-mouth disease virus (FMDV) RNA-dependent RNA polymerase allows FMDV to exhibit high genetic diversity. Previously, we showed that the genetic diversity of FMDV plays an important role in virulence in suckling mice. Here, we mutated the amino acid residue Phe257, located in the finger domain of FMDV polymerase and conserved across FMDV serotypes, to a cysteine (F257C) to study the relationship between viral genetic diversity, virulence, and transmissibility in natural hosts. The single amino acid substitution in FMDV polymerase resulted in a high-fidelity virus variant, rF257C, with growth kinetics indistinguishable from those of wild-type (WT) virus in cell culture, but it displayed smaller plaques and impaired fitness in direct competition assays. Furthermore, we found that rF257C was attenuated in vivo in both suckling mice and pigs (one of its natural hosts). Importantly, contact exposure experiments showed that the rF257C virus exhibited reduced transmissibility compared to that of wild-type FMDV in the porcine model. This study provides evidence that FMDV genetic diversity is important for viral virulence and transmissibility in susceptible animals. Given that type O FMDV exhibits the highest genetic diversity among all seven serotypes of FMDV, we propose that the lower polymerase fidelity of the type O FMDV could contribute to its dominance worldwide.IMPORTANCE Among the seven serotypes of FMDV, serotype O FMDV have the broadest distribution worldwide, which could be due to their high virulence and transmissibility induced by high genetic diversity. In this paper, we generated a single amino acid substitution FMDV variant with a high-fidelity polymerase associated with viral fitness, virulence, and transmissibility in a natural host. The results highlight that maintenance of viral population diversity is essential for interhost viral spread. This study provides evidence that higher genetic diversity of type O FMDV could increase both virulence and transmissibility, thus leading to their dominance in the global epidemic.

Senecavirus-Specific Recombination Assays Reveal the Intimate Link between Polymerase Fidelity and RNA Recombination.

Senecavirus A (SVA) is a reemerging virus, and recent evidence has emphasized the importance of SVA recombination in vivo on virus evolution. In this study, we report the development of an infectious cDNA clone for the SVA/HLJ/CHA/2016 strain. We used this strain to develop a reporter virus expressing enhanced green fluorescent protein (eGFP), which we then used to screen for a recombination-deficient SVA by an eGFP retention assay. Sequencing of the virus that retained the eGFP following passage allowed us to identify the nonsynonymous mutations (S460L alone and I212V-S460L in combination) in the RNA-dependent RNA polymerase (RdRp) region of the genome. We developed a Senecavirus-specific cell culture-based recombination assay, which we used to elucidate the role of RdRp in SVA recombination. Our results demonstrate that these two polymerase variants (S460L and I212/S460L) have reduced recombination capacity. These results indicate that the RdRp plays a central role in SVA replicative recombination. Notably, our results showed that the two recombination-deficient variants have higher replication fidelity than the wild type (WT) and display decreased ribavirin sensitivity compared to the WT. In addition, these two mutants exhibited significantly increased fitness in vitro compared to the WT. These results demonstrate that recombination and mutation rates are intimately linked. Our results have important implications for understanding the crucial role of the RdRp in virus recombination and fitness, especially in the molecular mechanisms of SVA evolution and pathogenicity.IMPORTANCE Recent evidence has emphasized the importance of SVA recombination on virus evolution in vivo We describe the first assays to study Senecavirus A recombination. The results show that the RNA-dependent RNA polymerase plays a crucial role in recombination and that recombination can impact the fitness of SVA in cell culture. Further, SVA polymerase fidelity is closely related to recombination efficiency. The results provide key insights into the role of recombination in positive-strand RNA viruses.

Black carbon derived from pyrolysis of maize straw and polystyrene microplastics affects soil biodiversity.

Understanding the environmental correlation of microbial community under external stimulation is significant for ecological restoration. However, few studies focused on the response of soil biodiversity induced by black carbon (BC) derived from pyrolysis of straw and microplastics (MPs) due to their widespread existence in natural environment. In this study, polystyrene MPs (PS) and maize straw with different mass ratios were used as raw materials to prepare BC by pyrolysis. The surface morphology, chemical composition and sequential variations of different functional groups of BC were systematically analyzed. The leachate from BC was identified by three-dimensional excitation emission matrice (3D-EEM). The corresponding results showed that yield, value of O/C and N element content of BC decreased with more PS. The changed C content and oxygen-containing functional groups occurred. The order of functional groups of BC formed by co-pyrolysis was: C=C > C-O > C-H > Si-O-Si. The main component of leaching from BC was humic-like and fulvic-like acid. Simultaneously, the input of exogenous BC into soil affected abundance, composition and metabolic pathways of microorganisms. The study helps to understand environmental implication of BC which was pyrolyzed from maize straw and MPs, providing an idea for improving biogeochemical cycle process in soil.

A comparison of the use of contrast media with different iodine concentrations for enhanced computed tomography.

Objective: In this study, we compared the enhancement of blood vessels and liver parenchyma on enhanced computed tomography (CT) of the upper abdomen with two concentrations of contrast media (400 and 300 mg I/mL) based on similar iodine delivery rate (IDR) of 0.88 and 0.9 g I/s and iodine load of 450 mg I/kg. Methods: We randomly assigned 160 patients into two groups: iomeprol 400 mg I/mL (A group) and iohexol 300 mg I/mL (B group). The CT attenuation values of the main anatomical structures in the two groups with different scanning phases were measured and the image quality of the two groups was analyzed and compared. The peak pressure and local discomfort (including fever and pain) during contrast medium injection were recorded. Results: The mean attenuation value of the abdominal aorta was 313.6 ± 29.6 in the A group and 322.4 ± 30.1 in the B group during the late arterial phase (p = 0.8). Meanwhile, the mean enhancement values of the portal vein were 176.2 ± 19.3 and 165.9 ± 24.5 in the A and B groups, respectively, during the portal venous phase (p = 0.6). The mean CT values of liver parenchyma were 117.1 ± 15.3 and 108.8 ± 18.7 in the A and B groups, respectively, during the portal venous phase (p = 0.9). There was no statistical difference in image quality, peak injection pressure (psi), and local discomfort between the two groups (p > 0.05). Conclusion: When a similar IDR and the same iodine load are used, CT images with different concentrations of contrast media have the same subjective and objective quality, and can meet the diagnostic needs.

The Stem-Loop I of Senecavirus A IRES Is Essential for Cap-Independent Translation Activity and Virus Recovery.

Senecavirus A (SVA) is a picornavirus that causes vesicular disease in swine and the only member of the Senecavirus genus. Like in all members of Picornaviridae, the 5' untranslated region (5'UTR) of SVA contains an internal ribosome entry site (IRES) that initiates cap-independent translation. For example, the replacement of the IRES of foot-and-mouth disease virus (FMDV) with its relative bovine rhinitis B virus (BRBV) affects the viral translation efficiency and virulence. Structurally, the IRES from SVA resembles that of hepatitis C virus (HCV), a flavivirus. Given the roles of the IRES in cap-independent translation for picornaviruses, we sought to functionally characterize the IRES of this genus by studying chimeric viruses generated by exchanging the native SVA IRES with that of HCV either entirely or individual domains. First, the results showed that a chimeric SVA virus harboring the IRES from HCV, H-SVA, is viable and replicated normally in rodent-derived BHK-21 cells but displays replication defects in porcine-derived ST cells. In the generation of chimeric viruses in which domain-specific elements from SVA were replaced with those of HCV, we identified an essential role for the stem-loop I element for IRES activity and recombinant virus recovery. Furthermore, a series of stem-loop I mutants allowed us to functionally characterize discrete IRES regions and correlate impaired IRES activities, using reporter systems with our inability to recover recombinant viruses in two different cell types. Interestingly, mutant viruses harboring partially defective IRES were viable. However, no discernable replication differences were observed, relative to the wild-type virus, suggesting the cooperation of additional factors, such as intermolecular viral RNA interactions, act in concert in regulating IRES-dependent translation during infection. Altogether, we found that the stem-loop I of SVA is an essential element for IRES-dependent translation activity and viral replication.