tailed bacteriophages fall within which of baltimore groups
Caudovirales The Caudovirales are an order of viruses also known as the tailed bacteriophages (cauda is Latin for "tail").[1] Under the Baltimore classification scheme, the Caudovirales are group I viruses as they have double stranded DNA (dsDNA) genomes, which can be anywhere from 18,000 base pairs to 500,000 base pairs in length.[2] The virus particles have a distinct shape; each virion has an icosahedral head that contains the viral genome, and is attached to a flexible tail by a connector protein.[2] The order encompasses a wide range of viruses, many of which containing genes of similar nucleotide sequence and function. Some tailed bacteriophage genomes can vary quite significantly in nucleotide sequence, however, even among the same genus. Due to their characteristic structure and possession of potentially homologous genes, it is believed these bacteriophages possess a common origin.[2]
Bacteria The ancestors of modern bacteria were unicellular microorganisms that were the first forms of life to appear on Earth, about 4 billion years ago. For about 3 billion years, most organisms were microscopic, and bacteria and archaea were the dominant forms of life.[20][21] Although bacterial fossils exist, such as stromatolites, their lack of distinctive morphology prevents them from being used to examine the history of bacterial evolution, or to date the time of origin of a particular bacterial species. However, gene sequences can be used to reconstruct the bacterial phylogeny, and these studies indicate that bacteria diverged first from the archaeal/eukaryotic lineage.[22] The most recent common ancestor of bacteria and archaea was probably a hyperthermophile that lived about 2.5 billionâ€“3.2 billion years ago.[23][24]