Environmental Microbiology of Aquatic and Waste Systems

102 4 Taxonomy, Physiology, and Ecology of Aquatic Microorganisms

9 PlASMAVIRIDAE

Structure
Pleomorphic, envelope, lipids, no capsid, circular supercoiled
dsDNA. Enveloped, spherical to pleomorphic, no head­tail
structure. The capsid is about 80 nm in diameter.
The Plasmaviridae is a family of bacteriophages, viruses that
infects bacteria. Virions have an envelope, a nucleoprotein com­
plex, and a capsid. They are 50-125 nm in diameter with a baggy
or loose membrane.
The genome is condensed, non segmented and consists of a
single molecule of circular, supercoiled double­stranded DNA,

12000 base pairs in length. The genome has a rather high G-C

content of around 32 percent.

A productive infectious cycle begins before a lysogenic

cycle establishes the virus in the infected bacteria. After initial

infection of the viral genome the virus may become latent

within the host. Lysogeny involves integration into the host

chromosome.

Host

A well­known host is Acholeplasma.

Capsid

gp10A,gp10B

Head

Tail

T=7

Inner

core

gp16

gp15

gp14

gp6,gp7

gp11,gp12

Tail fiber

gp17

Connector

gp8

 ViralZone 2009

Swiss Institute of Bioinformatics

10 PODOVIRIDAE

Structure
Nonenveloped, head­tail structure. Head is about 60 nm in diam­
eter. The tail is non­contractile, has 6 short subterminal fibers.
The capsid is icosahedral with a T=7 symmetry.
It has a linear, dsDNA genome of about 40-42 kb encoding
for 55 genes.

Host

Wide range of bacterial hosts including Gram positive and Gram

negative.