Improving human coronavirus OC43 (HCoV-OC43) research comparability in studies using HCoV-OC43 as a surrogate for SARS-CoV-2.

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic has renewed interest in human coronaviruses that cause the common cold, particularly as research with them at biosafety level (BSL)-2 avoids the added costs and biosafety concerns that accompany work with SARS-CoV-2, BSL-3 research. One of these, human coronavirus OC43 (HCoV-OC43), is a well-matched surrogate for SARS-CoV-2 because it is also a Betacoronavirus, targets the human respiratory system, is transmitted via respiratory aerosols and droplets and is relatively resistant to disinfectants. Unfortunately, growth of HCoV-OC43 in the recommended human colon cancer (HRT-18) cells does not produce obvious cytopathic effect (CPE) and its titration in these cells requires expensive antibody-based detection. Consequently, multiple quantification approaches for HCoV-OC43 using alternative cell lines exist, which complicates comparison of research results. Hence, we investigated the basic growth parameters of HCoV-OC43 infection in three of these cell lines (HRT-18, human lung fibroblasts (MRC-5) and African green monkey kidney (Vero E6) cells) including the differential development of cytopathic effect (CPE) and explored reducing the cost, time and complexity of antibody-based detection assay. Multi-step growth curves were conducted in each cell type in triplicate at a multiplicity of infection of 0.1 with daily sampling for seven days. Samples were quantified by tissue culture infectious dose50(TCID50)/mL or plaque assay (cell line dependent) and additionally analyzed on the Sartorius Virus Counter 3100 (VC), which uses flow virometry to count the total number of intact virus particles in a sample. We improved the reproducibility of a previously described antibody-based detection based TCID50 assay by identifying commercial sources for antibodies, decreasing antibody concentrations and simplifying the detection process. The growth curves demonstrated that HCoV-O43 grown in MRC-5 cells reached a peak titer of ˜107 plaque forming units/mL at two days post infection (dpi). In contrast, HCoV-OC43 grown on HRT-18 cells required six days to reach a peak titer of ˜106.5 TCID50/mL. HCoV-OC43 produced CPE in Vero E6 cells but these growth curve samples failed to produce CPE in a plaque assay after four days. Analysis of the VC data in combination with plaque and TCID50 assays together revealed that the defective:infectious virion ratio of MRC-5 propagated HCoV-OC43 was less than 3:1 for 1-6 dpi while HCoV-OC43 propagated in HRT-18 cells varied from 41:1 at 1 dpi, to 329:4 at 4 dpi to 94:1 at 7 dpi. These results should enable better comparison of extant HCoV-OC43 study results and prompt further standardization efforts.

Molecular systematics of two enigmatic genera Psittacella and Pezoporus illuminate the ecological radiation of Australo-Papuan parrots (Aves: Psittaciformes).

The platycercine parrots of Australia, usually recognized as the Platycercinae or Platycercini, are the broad-tailed parrots and their allies typified by the rosellas Platycercus spp. Debate concerning their circumscription has most recently centerd on the position of four genera, Neophema, Neopsephotus, Pezoporus and Psittacella, the last two having never been adequately included in sequence-based analyses. We use broad taxon sampling, mitochondrial and nuclear DNA sequence data from seven independent loci (two linked mitochondrial loci and six nuclear loci), and both gene tree and species tree approaches to reconstruct phylogenies and so determine the systematic placement all four genera. Analyses of two data sets, one of 48 taxa and five loci and one of 27 taxa and the same five plus three additional loci produced broadly congruent and consistently well-resolved phylogenies. We reject placement of any of these four genera within core platycercines. Pezoporus is closely allied to Neophema and Neopsephotus. These three genera are the likely sister group to core platycercines and we advocate their recognition as a subfamily. Psittacella is the sole extant representative of a lineage that branched very early in the history of Australo-Papuan parrot fauna and is not closely related to any of the mostly south-east Asian and Indonesian psittaculine taxa with which it is more often linked. We present a revised view of the extraordinary phylogenetic, phenotypic and ecological diversity that is the adaptive radiation of Australo-Papuan parrots. Finally, our analyses highlight the likely paraphyly of Mayr's (2008) Loricoloriinae.

A multilocus molecular phylogeny of the parrots (Psittaciformes): support for a Gondwanan origin during the cretaceous.

The question of when modern birds (Neornithes) first diversified has generated much debate among avian systematists. Fossil evidence generally supports a Tertiary diversification, whereas estimates based on molecular dating favor an earlier diversification in the Cretaceous period. In this study, we used an alternate approach, the inference of historical biogeographic patterns, to test the hypothesis that the initial radiation of the Order Psittaciformes (the parrots and cockatoos) originated on the Gondwana supercontinent during the Cretaceous. We utilized broad taxonomic sampling (representatives of 69 of the 82 extant genera and 8 outgroup taxa) and multilocus molecular character sampling (3,941 bp from mitochondrial DNA (mtDNA) genes cytochrome oxidase I and NADH dehydrogenase 2 and nuclear introns of rhodopsin intron 1, tropomyosin alpha-subunit intron 5, and transforming growth factor ss-2) to generate phylogenetic hypotheses for the Psittaciformes. Analyses of the combined character partitions using maximum parsimony, maximum likelihood, and Bayesian criteria produced well-resolved and topologically similar trees in which the New Zealand taxa Strigops and Nestor (Psittacidae) were sister to all other psittaciforms and the cockatoo clade (Cacatuidae) was sister to a clade containing all remaining parrots (Psittacidae). Within this large clade of Psittacidae, some traditionally recognized tribes and subfamilies were monophyletic (e.g., Arini, Psittacini, and Loriinae), whereas several others were polyphyletic (e.g., Cyclopsittacini, Platycercini, Psittaculini, and Psittacinae). Ancestral area reconstructions using our Bayesian phylogenetic hypothesis and current distributions of genera supported the hypothesis of an Australasian origin for the Psittaciformes. Separate analyses of the timing of parrot diversification constructed with both Bayesian relaxed-clock and penalized likelihood approaches showed better agreement between geologic and diversification events in the chronograms based on a Cretaceous dating of the basal split within parrots than the chronograms based on a Tertiary dating of this split, although these data are more equivocal. Taken together, our results support a Cretaceous origin of Psittaciformes in Gondwana after the separation of Africa and the India/Madagascar block with subsequent diversification through both vicariance and dispersal. These well-resolved molecular phylogenies will be of value for comparative studies of behavior, ecology, and life history in parrots.