The use of informativity in the development of robust viromics-based examinations

Freshwater Viromes: From Sampling to Evaluation

There are a number of options available to researchers who wish to collect and analyze viral metagenomes (viromes) from environmental samples. Here we describe a laboratory procedure for generation of viromes from freshwater samples, specifically targeting dsDNA bacteriophages. We also discuss methods for bioinformatic analysis of the resulting data.

Pseudomonas PB1-Like Phages: Whole Genomes from Metagenomes Offer Insight into an Abundant Group of Bacteriophages

Despite the abundance, ubiquity and impact of environmental viruses, their inherent genomic plasticity and extreme diversity pose significant challenges for the examination of bacteriophages on Earth. Viral metagenomic studies have offered insight into broader aspects of phage ecology and repeatedly uncover genes to which we are currently unable to assign function. A combined effort of phage isolation and metagenomic survey of Chicago’s nearshore waters of Lake Michigan revealed the presence of Pbunaviruses, relatives of the Pseudomonas phage PB1. This prompted our expansive investigation of PB1-like phages. Genomic signatures of PB1-like phages and Pbunaviruses were identified, permitting the unambiguous distinction between the presence/absence of these phages in soils, freshwater and wastewater samples, as well as publicly available viral metagenomic datasets. This bioinformatic analysis led to the de novo assembly of nine novel PB1-like phage genomes from a metagenomic survey of samples collected from Lake Michigan. While this study finds that Pbunaviruses are abundant in various environments of Northern Illinois, genomic variation also exists to a considerable extent within individual communities.

Construction of a Comprehensive Database from the Existing Viral Sequences Available from the International Nucleotide Sequence Database Collaboration

The progress in viromics research has led to the accumulation of a large number of sequences from different types of viruses obtained from different sources. Most databases are specific to different of species or types of viruses. However, raw sequences, as deposited in the reliable online collections, provide a valuable asset in the exploration of genomic and metagenomics datasets.The International Nucleotide Sequence Database Collaboration (INSDC) is the largest coordinated effort for compiling, sharing, and maintaining the most comprehensive collections of nucleic acids deposited throughout the most important public databases. The compendium includes different types of data such as complete genomes, genes, expressed sequence tags, and data generated by whole genome shotgun analyses spanning all domains of life, as well as the most complete collection of viral sequences available online.This chapter presents simplified computational methods for the automation of viral nucleotide sequence retrieval from online repositories of the INSDC databases, including all available sequences, except synthetic ones. The subsequent steps can be used for obtaining the taxonomy (including ranks: virus type, baltimore classification, order, family, subfamily, genus and species), and split the database into species subsets to dereplicate the sequences for other downstream applications. Only basic computational knowledge is required.

Kullback Leibler divergence in complete bacterial and phage genomes

The amino acid content of the proteins encoded by a genome may predict the coding potential of that genome and may reflect lifestyle restrictions of the organism. Here, we calculated the Kullback–Leibler divergence from the mean amino acid content as a metric to compare the amino acid composition for a large set of bacterial and phage genome sequences. Using these data, we demonstrate that (i) there is a significant difference between amino acid utilization in different phylogenetic groups of bacteria and phages; (ii) many of the bacteria with the most skewed amino acid utilization profiles, or the bacteria that host phages with the most skewed profiles, are endosymbionts or parasites; (iii) the skews in the distribution are not restricted to certain metabolic processes but are common across all bacterial genomic subsystems; (iv) amino acid utilization profiles strongly correlate with GC content in bacterial genomes but very weakly correlate with the G+C percent in phage genomes. These findings might be exploited to distinguish coding from non-coding sequences in large data sets, such as metagenomic sequence libraries, to help in prioritizing subsequent analyses.

New insight into the RNA aquatic virosphere via viromics

RNA viruses that infect microbes are now recognized as an active, persistent and important component of the aquatic microbial community. While some information about the diversity and dynamics of the RNA virioplankton has been derived from culture-based and single gene approaches, research based on viromic and metatransciptomic methods has generated unprecedented insight into this relatively understudied class of microbes. Here, the relevant literature is summarized and discussed, including viromic studies of extracellular aquatic RNA viral assemblages, and transcriptomic studies of active and associated RNA viruses from aquatic environments followed by commentary on the present challenges and future directions of this field of research.