Environmental Microbiology of Aquatic and Waste Systems

94 4 Taxonomy, Physiology, and Ecology of Aquatic Microorganisms

Bacteriophages are the most abundant among the
phages and they have been more widely studied.
Bacteriophages were first formally described by the
French Canadian Felix d’ Herelle in 1915, but the ini­
tial observations were made during 1896, followed by
observations made by the British bacteriologist
Frederick Twort in 1913 (see Fig. 4.2 6 ). On account of
their importance in aquatic systems, the life cycle of
bacterial viruses, the methods of isolating and enumer­
ating them from water, their grouping, and their host
range will be discussed below.

Life History of Bacteriophages

When bacteriophages enter susceptible bacteria, they

take over the genetic apparatus of their hosts and force

the hosts to produce more viruses of their type. When

the virions (virus particles) mature, they produce

enzymes which lyse the host cell wall releasing the

virus particle to start life afresh. When they lyse the

host they are in the lytic phase.

Sometimes they enter into a phase, the lysogenic phase,

in which the phages remain in the cell and replicate with it.

This phase is the lysogenic phase (see Fig. 4.2 7 ).

Order Mononegavirales
Family
Subfamily Genus Type species Hosts
Rhabdoviridae Vesiculovirus Vesicular stomatitis Indiana virus Vertebrates,
invertebrates
Lyssavirus Rabies virus Vertebrates
Ephemerovirus Bovine ephemeral fever virus Vertebrates,
invertebrates
Novirhabdovirus Infectious hematopoetic necrosis
virus

Vertebrates

Cytorhabdovirus Lettuce necrotic yellows virus Plants,
invertebrates
Nucleorhabdovirus Potato yellow dwarf virus Plants,
invertebrates
Arenaviridae Arenavirus Lymphocytic choriomeningitis
virus

Vertebrates

Bunyaviridae Orthobunyavirus Bunyamwera virus Vertebrates
Hantavirus Hantaan virus Vertebrates
Nairovirus Nairobi sheep disease virus Vertebrates
Phlebovirus Sandfly fever Sicilian virus Vertebrates
Tospovirus Tomato spotted wilt virus Plants
Deltavirus Hepatitis delta virus Vertebrates
Ophiovirus Citrus psorosis virus Plants
Orthomyxoviridae Influenza A virus Influenza A virus Vertebrates
Influenza B virus Influenza B virus Vertebrates
Influenza C virus Influenza C virus Vertebrates
Isavirus Infectious salmon anemia virus Vertebrates
Thogotovirus Thogoto virus Vertebrates
Tenuivirus Rice stripe virus Plants
Varicosaivirus Lettuce big­vein associated virus Plants
Note: Families are in uppercase and genera in bold starting with capital letters. The Order is represented in this case and is in larger
display than the family
RNA viruses are also designated according to the sense or polarity of their RNA into negative­sense and positive­sense, or ambisense.
Positive­sense viral RNA is similar to mRNA and thus can be immediately translated by the host cell. Negative­sense viral RNA is
complementary to mRNA and thus must be converted to positive­sense RNA by an RNA polymerase before translation. Ambisense
RNA viruses resemble negative­sense RNA viruses, except they also translate genes from the positive strand. They differ from those
of other negative­sense RNA viruses in that some proteins are coded in viral­complementary RNA sequences and others are coded
in the viral RNA sequence

Table 4.14 (continued)