Escherichia virus CC31, formerly known as Enterobacter virus CC31, is a dsDNA bacteriophage of the subfamily Tevenvirinae responsible for infecting the bacteria family of Enterobacteriaceae. It is one of two discovered viruses of the genus Karamvirus, diverging away from the previously discovered T4virus, as a clonal complex (CC). CC31 was first isolated from Escherichia coli B strain S/6/4 and is primarily associated with Escherichia, even though is named after Enterobacter.
Viral classification and structure
Enterobacter virus CC31 is a dsDNA virus lacking an RNA intermediate. The dsDNA is contained within an icosahedral capsid of proteins, but the virus lacks an envelope. It is in the order Caudovirales, being that it is a bacteriophage with a protein sheath and tail used to infect host cells. Caudovirales genetic material is contained within an icosahedral capsid resting on top of the sheath and tail. CC31 is in the Myoviridae family due to its lack of envelope, linear genome, and long, helical, permanent tail subunits. Tevenvirinae is the relatively large (43 genera) subfamily CC13 falls underneath. Finally, Cc13virus is the relatively new genus associated with Enterobacter virus CC31.
Genome
Enterobacter virus CC31 has a double stranded linear DNA (dsDNA) genome consisting of 165,540 nucleotide base pairs. The bases account for 287 genes that are capable of making 279 different proteins using 8 tRNAs. 93% of the genetic material is homologous with Enterobacter virus PG7, the other Tevenvirinae, and 74% of the material is homologous with the close relative Enterobacteria phage T-4. 120 new open reading frames (ORFs) were identified across the base pairs that were added to the Enterobacteria phage pan-genome. It is currently the only phage, that is not a T-even bacteriophage, capable of encoding for glycosyltransferases.
Genetic modification
The CC31 is capable of integrating its genetic material with the host's. This stage, known as the lysogenic cycle, halts particle formation, and allows for the virus's genetic material to amplify across many subsequent bacterium generations. The integration of the viral DNA happens non-homologously, forming bubbles of single stranded DNA. As DNA replication, crossing over, and cellular division occurs, the viral DNA is reshuffled with cellular DNA. This results in horizontal gene transfer between the virus and cell, resulting in the evolution of the virus and the bacterium. The viral DNA also develops minute deletions, immunity regions, and silent genetic regions due to the non-homologous binding of the DNA. These change in virus' genetic material can either inhibit or promote future replication.
Pathogenesis
In order for viral genomic replication to occur, CC31 needs to enter the host, Escherichia coli. Due to the lack of an outer envelope, the virion must find an alternate way to enter its host. It does this by penetrating the membrane of the bacterium with its tail region. First, the long tail fibers ejecting from the top of the base plate attach to the cell membrane of the bacterium. The small tail fibers underneath base plate then attach to the membrane, initiating a conformational change of the base plate to a six-point star from the previous hexagon conformation. This forces the sheath to undergo a conformational change to contract and effectively stretching the membrane. While this is occurring, the rigid tube underneath the sheath remains stagnant to push against the membrane. Digestion of the inner membrane occurs with the assistance of the tail's lysozymes. As this continues, the inner tube breaks through the membrane and allows the viral DNA to flow into the cytoplasm of the bacterium.