Segmented and multipartite viral genomes are both types of viruses where the genetic material is split into multiple parts, but they differ in how these parts are packaged and distributed among virions.
Segmented Viral Genomes
- Definition
- In viruses with a segmented genome, the genome is divided into several separate RNA or DNA molecules, each encoding one or more viral proteins.
- Packaging
- All segments are usually packaged into a single virion, allowing for complete infection and replication of the virus within one host cell.
- However, in some cases, segmented viruses can tolerate incomplete packaging, where not all segments are included in every virion.
- Genetic Exchange (Reassortment)
- Reassortment is a process where different viral strains infect the same cell and exchange genome segments, leading to rapid genetic variation. This is seen in Influenza viruses (e.g., Influenza A, which has 8 RNA segments).
- This contributes to viral evolution, enabling antigenic shifts that can cause pandemics.
- Advantages
- Allows for rapid genetic variation through reassortment.
- Efficient replication as all segments are generally co-packaged in the same virion.
- Examples
- Influenza virus (Orthomyxoviridae) – 8 RNA segments.
- Rotavirus (Reoviridae) – 11 RNA segments.
- Bunyaviruses – 3 RNA segments.
Multipartite Viral Genomes
- Definition
- A multipartite genome is divided into multiple nucleic acid molecules, but unlike segmented viruses, these genome segments are distributed across different virions, meaning that a complete set of virions is required to establish infection.
- Packaging
- Each segment is packaged into a separate virion, and to successfully infect a host, all necessary virions must infect the same host cell or organism.
- This can be inefficient because multiple particles are needed for a complete infection.
- Replication and Infection
- The host cell must receive multiple viral particles, each carrying a different genome segment, for productive infection to occur.
- This increases the likelihood of incomplete infection if all the necessary virions do not co-infect the same host.
- Advantages
- Potentially increases genetic diversity within a population of infected cells.
- Reduced genome size per virion may increase the efficiency of virion assembly and packaging.
- Disadvantages
- Higher risk of failed infection if all virions do not co-infect the same host.
- Lower efficiency compared to segmented viruses, which package all genome segments into one virion.
- Examples
- Nanoviridae (e.g., Banana bunchy top virus) – DNA segments.
- Partitiviruses – RNA segments.
- Faba bean necrotic yellows virus (Luteoviridae) – Multipartite RNA genome.
Comparison of Segmented vs. Multipartite
| Feature | Segmented Viruses | Multipartite Viruses |
|---|---|---|
| Genome Structure | Several genome segments in one virion | Genome segments distributed across multiple virions |
| Infection | A single virion can initiate infection | Multiple virions must infect for full genome delivery |
| Genetic Variation | Reassortment allows for genetic diversity | Limited genetic diversity compared to segmented viruses |
| Packaging | All genome segments co-packaged | Each segment in a separate virion |
| Efficiency of Infection | More efficient (only one virion needed) | Less efficient (multiple virions needed) |
