No abstract

SARS-CoV and SARS-CoV-2 have been thought to originate from bats. In this study, we screened pharyngeal and anal swabs from 13,064 bats collected between 2016 and 2021 at 703 locations across China for sarbecoviruses, covering almost all known southern hotspots, and found 146 new bat sarbecoviruses. Phylogenetic analyses of all available sarbecoviruses show that there are three different lineages, L1 as SARS-CoV related CoVs (SARSr-CoVs), L2 as SARS-CoV-2 related CoVs (SC2r-CoVs), and novel L-R (recombinants of L1 and L2) present in R. pusillus bats, in the mainland of China. Among the 146 sequences, only 4 are L-Rs. Importantly, none belongs in the L2 lineage, indicating that circulation of SC2r-CoVs in China might be very limited. All remaining 142 sequences belong in the L1 lineage, of which YN2020B-G shares the highest overall sequence identity with SARS-CoV (95.8%). The observation suggests endemic circulations of SARSr-CoVs, but not SC2r-CoVs, in bats in China. Geographic analysis of the collection sites in this study, together with all published reports, indicates that SC2r-CoVs may be mainly present in bats of Southeast Asia including the southern border of Yunnan province but absent in all other regions within China. In contrast, SARSr-CoVs appear to have broader geographic distribution, with the highest genetic diversity and sequence identity to human sarbecoviruses along the southwest border of China. Our data provide the rationale for further extensive surveys in broader geographical regions within, and beyond, Southeast Asia in order to find the most recent ancestors of human sarbecoviruses.

Severe acute respiratory syndrome coronavirus (SARS-CoV) and SARS-CoV-2 have been thought to originate from bat, but whether the cross-species transmission occurred directly from bat to human or through an intermediate host remains elusive. In this study, we performed CoV screening of 102 samples collected from animal-selling stalls of Wuhan Huanan Market (WHM) and pharyngeal and anal swabs from13,064 bats collected at 703 locations across China, covering almost all known southern hotspots for sarbecovirus, between 2016 and 2021. This is the first systematic survey of bat CoV in China during the outbreak of Corona Virus Disease 2019. We found four non-sarbeco CoVs in samples of WHM, and 142 SARS-CoV related CoVs (SARSr-CoV) and 4 recombinant CoVs in bats, of which YN2020B-G share the highest sequence identity with SARS-CoV among all known bat CoVs, suggesting endemic SARSr-CoVs in bats in China. However, we did not find any SARS-CoV-2 related CoVs (SC2r-CoV) in any samples, including specimens collected from the only two domestic places where RaTG13 and RmYN02 were previously reported (the Tongguan caves and the karst caves around the Xishuangbanna Tropical Botanical Garden), indicating that SC2r-CoVs might not actively circulate among bats in China. Phylogenetic analysis showed that there are three different lineages of sarbecoviruses, L1 (SARSr-CoV), L2 (SC2r-CoV), and L-R (a novel CoV lineage from L1 and L2 recombination), in China. Of note, L-R CoVs are only found in R. pusillus. Further macroscopical analysis of the genetic diversity, host specificity for colonization and accidental infection, and geographical characteristics of available CoVs in database revealed the presence of a general geographical distribution pattern for bat sarbecoviruses, with the highest genetic diversity and sequence homology to SARS-CoV or SARS-CoV-2 along the southwest border of China, the least in the northwest of China. Considering the receptor binding motifs for spike gene of sarbecoviruses in Indochina Peninsula show the greatest diversity, our data provide the rationale that extensive surveys in further south and southwest to or of China might be needed for finding closer ancestors of SARS-CoV and SARS-CoV-2.

A macromolecular nitrogen-phosphorous flame retardant combined with expandable graphite (EG) was employed to flameretard expanded polystyrene foam. As the intumescent char formation (catalyzed by the flame retardant) temperature overlaps with the expanding temperature of EG, their synchronous expansion occurs. In this process, the EG sheets can be embedded in the intumescent char and pushed forward to the surface with inflation of the composite chars, which greatly enhances the compactness and strength of the char layer, and better shields the heat and oxygen, as well as promotes the interactions of the degraded products of the polymer and the flame retardant. The limiting oxygen index (LOI), vertical flame and cone calorimeter tests showed that good flame retardance for the flame retardant EPSF could be achieved (LOI: 33.9%, UL94-V0 (1.6 mm) and remarkably decreased heat release rate). A series of characterizations-including char morphology observation scanning by electron microscope, surface elements determination through X-ray photoelectron spectroscopy, char strength test and thermogravimetric analysis-were performed to verify the synergistic mechanisms based on the synchronous expansion of the composite chars.

No abstract