Arch Virol (2007) 152: 227–243
Printed in The Netherlands
5500 Phages examined in the electron microscope
Department of Medical Biology, Faculty of Medicine, F´elix d’H´erelle Reference
Center for Bacterial Viruses, Laval University, Qu´ebec, Canada
Received May 12, 2006; accepted August 17, 2006
Published online October 19, 2006
Summary. “Phages” include viruses of eubacteria and archaea. At least 5568
phages have been examined in the electron microscope since the introduction
of negative staining in 1959. Most virions (96%) are tailed. Only 208 phages
(3.7%) are polyhedral, ﬁlamentous, or pleomorphic. Phages belong to one order,
17 families, and three “ﬂoating” groups. Phages are found in 11 eubacterial and
archaeal phyla and infect 154 host genera, mostly of the phyla Actinobacteria,
Firmicutes, and Proteobacteria. Of the tailed phages, 61% have long, noncontrac-
tile tails and belong to the family Siphoviridae. Convergent evolution is visible in
the morphology of certain phage groups.
“Phages” or bacteriophages are prokaryote viruses and include viruses of eu-
bacteria and archaea. They occur in vast numbers everywhere in the biosphere,
especially in the oceans [11, 12, 28]. In addition, most cultivable bacteria harbor
complete or defective prophages. Phages as a group are extremely diversiﬁed and
are arguably the oldest and most numerous of all viruses. The numbers of known
phages have been expanding for decades at a rate of approximately 100 per year.
Novel phages are continually reported in investigations of the environment and
industrial fermentations. Keeping track of them is one of the activities of the F´elix
d’H´erelle Reference Center for Bacterial Viruses.
The ﬁrst phage survey was published in 1967 and listed 111 negatively stained
phages, 99 of which were tailed. Three phages were isometric and nine were
ﬁlamentous . The latest surveys were made in 1995 and 2000. They included
4551 and 5136 phages, respectively [1, 2]. Over 96% of phages were tailed
and belonged to three families, the Myoviridae, Siphoviridae, and Podoviridae.