Environmental Microbiology of Aquatic and Waste Systems

4.1 Taxonomy of Microorganisms in Aquatic Environments 99

Genomic DNA

Integrase

Tail

Putative capsid

 2010

Swiss Institute of Bioinformatics

3 FuSSEllOVIRIDAE

Structure
Enveloped, lemon­shaped, with short tail fibers attached to one
pole. The virion is about 60 nm in diameter and 100 nm in length.
The genome of a fuselloviridae is non­segmented and con­
tains a single molecule of circular, double­stranded DNA. The
DNA is positively supercoiled. The complete genome is 15500
nucleotides in length; encodes for 31 to 37 genes.
Fuselloviridae virions consist of an envelope and a nucleo­
capsid. The capsid is enveloped. Virions are spindle­shaped,
flexible, and have protrusions that extend through the envelope.
One pole has short tail­like fibers attached to it. The virions are
100 nm in length and 60 nm in diameter.

Host

Fuselloviridae infect the Archae Sulfolobus which inhabits

high-temperature (>70°C), acidic (pH of <4.0) environments.

Members of this family have been found in acidic hotsprings in

Japan and Iceland. The Fuselloviridae family currently consists

of only one virus, Sulfolobus spindle­shaped virus 1 (SSV1),

and three tentative members (SSV2, SSV3, and the staaelite

virus pSSVx, which stands for plasmid SSV x). SSV1, the type

virus for the family, was the first high­temperature virus to be

characterized.

g6p

g3p

g8p

g7p

g9p

 ViralZone 2008

Swiss Institute of Bioinformatics

4 INOVIRIDAE

Structure
Non­enveloped, Rod of filaments ut 7nm in diameter and from
700 to 2000nm long.
Circular, single-stranded DNAof 4.5 to 8kb encoding for 4 to
10 proteins. Replication occurs via dsDNA intermediate and
rolling circle.

Host
Members of the family infect their natural hosts without causing
lysis, and the infected cells continue to divide and produce virus
indefinitely. The hosts are plant and animal pathogens. In several
systems the phage enter into lysogenic phases.
lnouirus hosts are all gram­negative bacteria (i.e., Escherichia
coli, Salmonella, Pseudomonas, Vibrio, Xanthomonas, etc.).

Host ranges are determined primarily by host cell receptors,

which are usually conjugative pili. Some pili are encoded chro­

mosomally and some are encoded on plasmids of different

incompatibility groups. Transmission of the plasmids to new

bacterial species usually transfers phage sensitivity. Additional

host range determinants include restriction­modification sys­

tems, host periplasmic proteins involved in viral ssDNA translo­

cation into the cytoplasm, and host protein(s) involved in

membrane assembly. Transfections of non­natural hosts with

naked ssDNA or dsDNA are sometimes possible. When Vibrio

cholera phage lysogens colonize the human intestine, states of

elevated cholera toxin expression and release, and of progeny

filamentous choleraphage extrusion, are induced. Thus lnaoirus

lysogeny is a critical virulence factor in cholera pathogenesis.