''Faustovirus'' is a genus of

giant virus A giant virus, sometimes referred to as a girus, is a very large virus, some of which are larger than typical bacteria. All known giant viruses belong to the phylum ''Nucleocytoviricota''. Description While the exact criteria as defined in the sc ...

which infects

amoeba An amoeba (; less commonly spelled ameba or amœba; : amoebas (less commonly, amebas) or amoebae (amebae) ), often called an amoeboid, is a type of Cell (biology), cell or unicellular organism with the ability to alter its shape, primarily by ...

e associated with humans. The virus was first isolated in 2015 and shown to be around 0.2 micrometers in diameter with a double stranded DNA

genome A genome is all the genetic information of an organism. It consists of nucleotide sequences of DNA (or RNA in RNA viruses). The nuclear genome includes protein-coding genes and non-coding genes, other functional regions of the genome such as ...

of 466 kilobases predicted to encode 451 proteins. Although classified as a

nucleocytoplasmic large DNA virus ''Nucleocytoviricota'' is a phylum of viruses. Members of the phylum are also known as the nucleocytoplasmic large DNA viruses (NCLDV), which serves as the basis of the name of the phylum with the suffix - for virus phylum. These viruses are refe ...

(NCLDV), faustoviruses share less than a quarter of their genes with other NCLDVs; however, ~46% are homologous to bacterial genes and the remainder are

orphan gene Orphan genes, ORFans, or taxonomically restricted genes (TRGs) are genes that lack a detectable homologue outside of a given species or lineage. Most genes have known homologues. Two genes are homologous when they share an evolutionary history, a ...

s (ORFans). Specifically, the gene encoding the major

capsid A capsid is the protein shell of a virus, enclosing its genetic material. It consists of several oligomeric (repeating) structural subunits made of protein called protomers. The observable 3-dimensional morphological subunits, which may or m ...

protein (MCP) of faustovirus is different than that of its most closely related giant virus, asfivirus, as well as other NCLDVs. In asfivirus, the gene encoding MCP is a single genomic fragment of ~2000

base pair A base pair (bp) is a fundamental unit of double-stranded nucleic acids consisting of two nucleobases bound to each other by hydrogen bonds. They form the building blocks of the DNA double helix and contribute to the folded structure of both DNA ...

s (bp), however, in faustovirus the MCP is encoded by 13 exons separated by 12 large

intron An intron is any nucleotide sequence within a gene that is not expressed or operative in the final RNA product. The word ''intron'' is derived from the term ''intragenic region'', i.e., a region inside a gene."The notion of the cistron .e., gen ...

s. The exons have a mean length of 149 bp and the introns have a mean length of 1,273 bp. The presence of introns in faustovirus genes is highly unusual for viruses. __TOC__

Replication

The replication strategy of faustovirus in amoeba is similar to that of

mimivirus ''Mimivirus'' is a genus of giant viruses, in the family ''Mimiviridae''. It is believed that Amoeba serve as their natural hosts. It also refers to a group of phylogenetically related large viruses. In colloquial speech, APMV is more commonly ...

. Lasting 18 to 20 hours, the replication cycle begins with the amoeba ingesting individual viral particles through a process known as

phagocytosis Phagocytosis () is the process by which a cell (biology), cell uses its plasma membrane to engulf a large particle (≥ 0.5 μm), giving rise to an internal compartment called the phagosome. It is one type of endocytosis. A cell that performs ph ...

. After about 2 to 4 hours post infection, virus particles are internalized via phagocytic vacuoles and are detected by the host. While the particles appear near the host's nucleus, there is no evidence that the virus is within the

nucleus Nucleus (: nuclei) is a Latin word for the seed inside a fruit. It most often refers to: *Atomic nucleus, the very dense central region of an atom *Cell nucleus, a central organelle of a eukaryotic cell, containing most of the cell's DNA Nucleu ...

or has an interaction with the nuclear membrane. Similar to the mimivirus, in which a channel is created for particle proteins and DNA to travel through, the faustovirus particles empty their internal compartments into the amoeba's

cytoplasm The cytoplasm describes all the material within a eukaryotic or prokaryotic cell, enclosed by the cell membrane, including the organelles and excluding the nucleus in eukaryotic cells. The material inside the nucleus of a eukaryotic cell a ...

. In both viruses, the fusion leads to an ''eclipse phase'' in which the contents of particles become invisible inside the cytoplasm of the host. However, the eclipse phase of the faustovirus is longer than the mimivirus, taking place from 4 to 6 hours post infection. Characterized by a loss of its spherical shape and a decrease in surface area, the amoeba host cell undergoes reorganization, such that at 8 to 10 hours post infection there are new particles in a region forming a donut shape. This region is the

viral factory A viroplasm, sometimes called "virus factory" or "virus inclusion", is an inclusion body in a cell where viral replication and assembly occurs. They may be thought of as viral factories in the cell. There are many viroplasms in one infected cell, w ...

; it is distinct from the nucleus and is surrounded by

mitochondria A mitochondrion () is an organelle found in the cells of most eukaryotes, such as animals, plants and fungi. Mitochondria have a double membrane structure and use aerobic respiration to generate adenosine triphosphate (ATP), which is us ...

. Between 12- and 18-hours post infection, the virus factory takes up the entirety of the cytoplasm, which is completely filled with new viral particles. At 18- to 20-hours post infection, the viral particles are released through cell

lysis Lysis ( ; from Greek 'loosening') is the breaking down of the membrane of a cell, often by viral, enzymic, or osmotic (that is, "lytic" ) mechanisms that compromise its integrity. A fluid containing the contents of lysed cells is called a ...

Pathogenicity

Faustovirus affects amoeba associated with the human environment, like ''Vermamoeba vermiformis''; this particular amoeba has been found in hospital water networks, drinking water, human stool samples, and contact lenses of

keratitis Keratitis is a condition in which the human eye, eye's cornea, the clear dome on the front surface of the eye, becomes inflammation, inflamed. The condition is often marked by moderate to intense pain and usually involves any of the following sy ...

patients, thus it may be a possible carrying agent for viruses. Faustoviruses have been found in sewage water from various geographical locations, such as Senegal, France, Lebanon, and Saudi Arabia. Isolated strains of the virus have been detected in rodents, cattle,

febrile Fever or pyrexia in humans is a symptom of an anti-infection defense mechanism that appears with body temperature exceeding the normal range caused by an increase in the body's temperature set point in the hypothalamus. There is no single agre ...

and healthy humans, and well water and rivers. Although faustovirus was found in humans, it is unknown whether it has a pathogenic effect on humans; more research is required to determine the mode of infection and consequences of infection, if any exist.

References

External links

* Nucleocytoplasmic large DNA viruses Asfarviridae {{Virus-stub