Understanding evolution of SARS‐CoV‐2: a perspective from analysis of genetic diversity of RdRp gene

Kasibhatla, Sunitha M.; Kinikar, Meenal; Limaye, Sanket; Kale, Mohan M.; Kulkarni‐Kale, Urmila

BACKGROUND & OBJECTIVES: COVID‐19 emerged as the first example of “Disease X”, a hypothetical disease of humans caused by an unknown infectious agent that was named as novel coronavirus and subsequently designated as SARS‐CoV‐2. The origin of the outbreak at the animal market in Wuhan, China implies it as a case of zoonotic spillover. The study was designed to understand evolution of Betacoronaviruses and in particular diversification of SARS‐CoV‐2 using RdRp gene, a stable genetic marker. METHODS: Phylogenetic and population stratification analyses were carried out using Maximum likelihood and Bayesian methods, respectively. RESULTS: Molecular phylogeny using RdRp, showed that SARS‐CoV‐2 isolates cluster together. Bat‐CoV isolate RaTG13 and Pangolin‐CoVs are observed to branch off prior to SARS‐CoV‐2 cluster. While SARS‐CoV form a single cluster, Bat‐CoVs form multiple clusters. Population‐based analyses revealed that both SARS‐CoV‐2 and SARS‐CoV form separate clusters with no admixture. Bat‐CoVs were found to have single and mixed ancestry and clustered as four sub‐populations. CONCLUSIONS: Population‐based analyses of Betacoronaviruses using RdRp, revealed that SARS‐CoV‐2 is a homogeneous population. SARS‐CoV‐2 appears to have evolved from Bat‐CoV isolate RaTG13, which diversified from a common ancestor from which Pangolin‐CoVs have also evolved. The admixed Bat‐CoV sub‐populations indicate that bats serve as reservoirs harboring virus ensembles that are responsible for zoonotic spillovers such as SARS‐CoV and SARS‐CoV‐2. The extent of admixed isolates of Bat‐CoVs observed in population diversification studies underline the need for periodic surveillance of bats and other animal reservoirs for potential spillovers as a measure towards preparedness for emergence of zoonosis. This article is protected by copyright. All rights reserved.