In the current COVID-19 pandemic, a significant proportion of cases shed SARS-Coronavirus-2 (SARS-CoV-2) with their faeces. To determine if SARS-CoV-2 RNA was present in sewage during the emergence of COVID-19 in The Netherlands, sewage samples of six cities and the airport were tested using four qRT-PCR assays, three targeting the nucleocapsid gene (N1−N3) and one the envelope gene (E). No SARS-CoV-2 RNA was detected on February 6, 3 weeks before the first Dutch case was reported. On March 4/5, one or more gene fragments were detected in sewage of three sites, in concentrations of 2.6−30 gene copies per mL. In Amersfoort, N3 was detected in sewage 6 days before the first cases were reported. As the prevalence of COVID-19 in these cities increased in March, the RNA signal detected by each qRT-PCR assay increased, for N1−N3 up to 790−2200 gene copies per mL. This increase correlated significantly with the increase in reported COVID-19 prevalence. The detection of the virus RNA in sewage, even when the COVID-19 prevalence is low, and the correlation between concentration in sewage and reported prevalence of COVID-19, indicate that sewage surveillance could be a sensitive tool to monitor the circulation of the virus in the population.

In the current COVID-19 pandemic, a significant proportion of cases shed SARS-Coronavirus-2 (SARS-CoV-2) with their faeces. To determine if SARS-CoV-2 is present in sewage during the emergence of COVID-19 in the Netherlands, sewage samples of 7 cities and the airport were tested using RT-PCR against three fragments of the nucleocapsid protein gene (N1-3) and one fragment of the envelope protein gene (E). No SARS-CoV-2 was detected in samples of February 6, three weeks before the first case was reported in the Netherlands on February 27. On March 5, the N1 fragment was detected in sewage of five sites. On March 15/16, the N1 fragment was detected in sewage of six sites, and the N3 and E fragment were detected at 5 and 4 sites respectively. This is the first report of detection of SARS-CoV-2 in sewage. The detection of the virus in sewage, even when the COVID-19 prevalence is low, indicates that sewage surveillance could be a sensitive tool to monitor the circulation of the virus in the population.

Analysing wastewater can be used to track infectious disease agents that are shed via stool and urine. Sewage surveillance of SARS-CoV-2 has been suggested as tool to determine the extent of COVID-19 in cities and serve as early warning for (re-)emergence of SARS-CoV-2 circulation in communities. The focus of this review is on the strength of evidence, opportunities and challenges for the application of sewage surveillance to inform public health decision making. Considerations for undertaking sampling programs are reviewed including sampling sites, strategies, sample transport, storage and quantification methods; together with the approach and evidence base for quantifying prevalence of infection from measured wastewater concentration. Published SARS-CoV-2 sewage surveillance studies (11 peer reviewed, and 10 pre-prints) were reviewed to demonstrate the current status of implementation to support public health decisions. Whilst being very promising, a number of areas were identified requiring additional research to further strengthen this approach and take full advantage of its potential. In particular, design of adequate sampling strategies, spatial and temporal resolution of sampling, sample storage, replicate sampling and analysis, controls for the molecular methods used for quantification of SARS-CoV-2 RNA in wastewater. The use of appropriate prevalence data and methods to correlate or even translate SARS-CoV-2 concentrations in wastewater to prevalence of virus shedders in the population is discussed.

The higher plant Arabidopsis thaliana (Arabidopsis) is an important model for identifying plant genes and determining their function. To assist biological investigations and to define chromosome structure, a coordinated effort to sequence the Arabidopsis genome was initiated in late 1996. Here we report one of the first milestones of this project, the sequence of chromosome 4. Analysis of 17.38 megabases of unique sequence, representing about 17% of the genome, reveals 3,744 protein coding genes, 81 transfer RNAs and numerous repeat elements. Heterochromatic regions surrounding the putative centromere, which has not yet been completely sequenced, are characterized by an increased frequency of a variety of repeats, new repeats, reduced recombination, lowered gene density and lowered gene expression. Roughly 60% of the predicted protein-coding genes have been functionally characterized on the basis of their homology to known genes. Many genes encode predicted proteins that are homologous to human and Caenorhabditis elegans proteins.

The spike (S) protein of murine coronavirus strain A59 (MHV-A59) is a type I membrane protein that induces membrane fusion. In this study we have analyzed the role of two domains in the S protein on fusion. The 180-kDa mature S protein is partially cleaved into two 90-kDa subunits during transport to the plasma membrane. We have identified several amino acids that are important for cleavage of S, and we show that cleavage is not strictly required for fusion. However, the level of cleavage seems to influence the fusion kinetics. After introduction of an arginine at position P2 to mimick the MHV-JHM cleavage site, full cleavage of the spike protein was obtained. Further, we analyzed the effect of mutations in the transmembrane (TM) domain of the S protein. Maturation and cell surface expression of the mutant proteins were not affected, and all proteins became acylated. The mutant in which the predicted transmembrane domain was shortened did not induce syncytia. From a group of mutants in which several conserved cysteines in the TM domain had been replaced by serines, one was unable to induce syncytia, another showed delayed syncytia formation, and the third mutant induced syncytia as did the wild-type protein. The potential role of the transmembrane domain in fusion is discussed.

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Coronavirus spike protein genes were expressed in vitro by using the recombinant vaccinia virus expression system. Recombinant spike proteins were expressed at the cell surface and induced cell fusion in a host-cell-dependent fashion. The intracellular transport of recombinant spike proteins was studied. The half time of acquisition of resistance to endo-,o-N-acetylglucosaminidase H was approximately 3 h for the recombinant feline infectious peritonitis virus S protein. The S protein in feline infectious peritonitis virus-infected cells was found to have a half time of acquisition of resistance to endo-jo-N-acetylglucosaminidase H of approximately 1 h. This difference can be explained by the fact that coronavirus budding takes place at intracellular membranes and that the oligosaccharides of the spike protein are modified after budding. Apparently, spike protein incorporated into budded virions is transported faster through the Golgi apparatus than is spike protein alone. These findings provide new insights into the mechanism of coronavirus budding and are discussed in relation to current models of intracellular transport and sorting of proteins.