Understanding the evolution and spread of chikungunya virus in the Americas using complete genome sequences

Local transmission of chikungunya virus (CHIKV) was first detected in the Americas in December 2013, after which it spread rapidly throughout the Caribbean islands and American mainland, causing a major chikungunya fever epidemic. Previous phylogenetic analysis of CHIKV from a limited number of countries in the Americas suggests that an Asian genotype strain was responsible, except in Brazil where both Asian and East/Central/South African (ECSA) lineage strains were detected. In this study, we sequenced thirty-three complete CHIKV genomes from viruses isolated in 2014 from fourteen Caribbean islands, the Bahamas and two mainland countries in the Americas. Phylogenetic analyses confirmed that they all belonged to the Asian genotype and clustered together with other Caribbean and mainland sequences isolated during the American outbreak, forming an 'Asian/American' lineage defined by two amino acid substitutions, E2 V368A and 6K L20M, and divided into two well-supported clades. This lineage is estimated to be evolving at a mean rate of 5 x 10-4 substitutions per site per year (95% higher probability density, 2.9-7.9 x 10-4) and to have arisen from an ancestor introduced to the Caribbean (most likely from Oceania) in about March 2013, 9 months prior to the first report of CHIKV in the Americas. Estimation of evolutionary rates for individual gene regions and selection analyses indicate that (in contrast to the Indian Ocean Lineage that emerged from the ECSA genotype followed by adaptive evolution and with a significantly higher substitution rate) the evolutionary dynamics of the Asian/American lineage are very similar to the rest of the Asian genotype and natural selection does not appear to have played a major role in its emergence. However, several codon sites with evidence of positive selection were identified within the non-structural regions of Asian genotype sequences outside of the Asian/American lineage

Finding a Needle in the Virus Metagenome Haystack - Micro-Metagenome Analysis Captures a Snapshot of the Diversity of a Bacteriophage Armoire

Viruses are ubiquitous in the oceans and critical components of marine microbial communities, regulating nutrient transfer to higher trophic levels or to the dissolved organic pool through lysis of host cells. Hydrothermal vent systems are oases of biological activity in the deep oceans, for which knowledge of biodiversity and its impact on global ocean biogeochemical cycling is still in its infancy. In order to gain biological insight into viral communities present in hydrothermal vent systems, we developed a method based on deep-sequencing of pulsed field gel electrophoretic bands representing key viral fractions present in seawater within and surrounding a hydrothermal plume derived from Loki's Castle vent field at the Arctic Mid-Ocean Ridge. The reduction in virus community complexity afforded by this novel approach enabled the near-complete reconstruction of a lambda-like phage genome from the virus fraction of the plume. Phylogenetic examination of distinct gene regions in this lambdoid phage genome unveiled diversity at loci encoding superinfection exclusion- and integrase-like proteins. This suggests the importance of fine-tuning lyosgenic conversion as a viral survival strategy, and provides insights into the nature of host-virus and virus-virus interactions, within hydrothermal plumes. By reducing the complexity of the viral community through targeted sequencing of prominent dsDNA viral fractions, this method has selectively mimicked virus dominance approaching that hitherto achieved only through culturing, thus enabling bioinformatic analysis to locate a lambdoid viral “needle" within the greater viral community “haystack". Such targeted analyses have great potential for accelerating the extraction of biological knowledge from diverse and poorly understood environmental viral communities

Towards an integrative view of virus phenotypes

Understanding how phenotypes emerge from genotypes is a foundational goal in biology. As challenging as this task is when considering cellular life, it is further complicated in the case of viruses. During replication, a virus as a discrete entity (the virion) disappears and manifests itself as a metabolic amalgam between the virus and the host (the virocell). Identifying traits that unambiguously constitute a virus’s phenotype is straightforward for the virion, less so for the virocell. Here, we present a framework for categorizing virus phenotypes that encompasses both virion and virocell stages and considers functional and performance traits of viruses in the context of fitness. Such an integrated view of virus phenotype is necessary for comprehensive interpretation of viral genome sequences and will advance our understanding of viral evolution and ecology