Cystoviridae

Cystoviridae is a family of double-stranded RNA viruses that primarily infect bacteria, specifically the Pseudomonas species. This family is unique among bacteriophages due to its double-stranded RNA genome, which is segmented into three parts. The family is named after its prototype member, Pseudomonas phage phi6.

Structure

Cystoviridae virions are non-enveloped and possess an icosahedral capsid with a diameter of approximately 85 nm. The capsid is composed of protein subunits that form a protective shell around the viral genome. Inside the capsid, the genome is divided into three segments, designated as L (large), M (medium), and S (small), each encoding different viral proteins essential for the virus's life cycle.

Genome

The genome of Cystoviridae is composed of three segments of double-stranded RNA:

• Segment L: Encodes the RNA-dependent RNA polymerase and other proteins involved in replication.
• Segment M: Encodes proteins involved in host cell entry and membrane fusion.
• Segment S: Encodes the capsid proteins and other structural components.

The segmented nature of the genome allows for reassortment, which can lead to genetic diversity and evolution within the family.

Replication Cycle

The replication cycle of Cystoviridae begins with the attachment of the virus to the host cell surface via specific receptors. Following attachment, the virus injects its RNA segments into the host cell cytoplasm. The RNA-dependent RNA polymerase, encoded by the L segment, synthesizes mRNA from the viral RNA templates. These mRNAs are then translated into viral proteins by the host's ribosomes.

The newly synthesized viral proteins and RNA segments assemble into progeny virions within the host cell. The mature virions are released from the host cell through lysis, which results in the death of the host bacterium.

Host Range

Cystoviridae primarily infects bacteria of the genus Pseudomonas, which are common in soil and water environments. The most studied member of this family, Pseudomonas phage phi6, has been used extensively as a model organism for studying virus-host interactions and the mechanisms of RNA virus replication.

Research and Applications

Cystoviridae has been a valuable model for understanding the biology of double-stranded RNA viruses. Studies on Cystoviridae have provided insights into viral replication, assembly, and evolution. Additionally, due to their ability to infect bacteria, Cystoviridae phages are being explored as potential tools for phage therapy, an alternative to antibiotics for treating bacterial infections.

Also see

• Bacteriophage
• Double-stranded RNA virus
• Pseudomonas
• Phage therapy