CYANOPHAGES - Cyanobacteria - page 426

coli-phages are described (Moisa et al ., 1981b). A temperate cyanophage NP-1T, discovered by
Muradov et al . (1990a,b) from Russia, is unique because it infects and lysogenizes heterocystous
nitrogen-fi xing cyanobacterium Nostoc on the one hand and non-heterocystous fi lamentous Plectonema
on the other. The phage capsid has a diameter of 78 nm and lacks a distinct tail. DNA of the phage
has a mean contour length of 14.4 µm and molecular mass of 28MDa. The specifi city of the phage
was confi rmed from the data on restriction analysis using the EcoRV enzyme that hydrolyses DNA of
cyanophages to yield different number of fragments. Ma-LBP, a cyanophage infecting M . aeruginosa
has been isolated from Lake Baroon, Sunshine Coast, Queensland, Australia by Tucker and Pollard
(2005). Two strains of the virus of Ma-LBP (a podovirus), resembling T7 in their morphology, have
been detected with short stubby tails but the head diameters varied by 10 nm. In one of the strains
the head diameter was 42 nm whereas in the second it was 52 nm. The virus had a latent period of
11.2 h with an average burst size of 28 virus particles per host cell. The titer of the virus from lake
waters was found to be 5.6 x 10 4 ml -1 that represents 0.23% of the natural viral population of the
Lake (2.46 x 10 7 ml -1 ). In view of this the authors concluded that the virus controls the populations
of Microcystis .
V. CYANOPHAGES OF UNCERTAIN IDENTITY
A number of cyanophages isolated on P . boryanum such as P-2, P-3, P-4 (Singh and Singh, 1967), P-5,
and P-6 (Singh et al ., 1972) are included here primarily because they sensitize the same host strain
( P . boryanum ) with minor differences in plaque morphology, latent period etc. The cyanophages P-2
to P-6 have not been either morphologically or serologically characterized for relationships amongst
themselves or with those of others, described above infecting Plectonema .
The cyanophage C-1 sensitizing Cylindrospermum sp. (Singh and Singh, 1967), AR-1 attacking
Anabaenopsis raciborskii , A . circularis and Raphidiopsis indica (Singh and Singh 1967), AR-2 that infects
A . raciborskii (Singh et al ., 1972) and A-1 (Singh et al ., 1972) are the other cyanophages discovered
causing lysis of the nitrogen fi xing cyanobacteria from India. Of these cyanophages, A-1 which
sensitizes Anabaena cylindrica is of special interest because of its unique morphology amongst the
hither to discovered freshwater cyanophages. The phage possesses a sheath of 20 nm broad and 100
nm long. A tail or wick of 130-300 nm long is attached to sheath. These particles are headless. It is
suspected that they contain RNA, and their morphology brings them closer to raphidosomes reported
in Saprospira grandis (Lewin, 1963) and Actinomyces streptomycini (Rautenstein et al ., 1966).
Kaushik and Venkataramn (1973) described a cyanophage TAuHN-1 infecting Tolypothrix tenuis ,
Aulosira fertilissima , N . muscorum and Hapalosiphon intricatus . A series of viruses belonging to A-4L
and N-L infecting A. variabilis , Nostoc linckia and S-8K and S-2L infecting Synechococcus , respectively
have been isolated from Russia (Gromov, 1983). Trivedi and Oza (1979) reported the isolation of
cyanophage O-1 active against Oscillatoria chlorina from Ahmedabad. The phage is a slender rod
having a diameter of 25 nm and a length of 300 nm.
Phlips et al . (1990) reported the lysis of M . aeruginosa by a cyanophage designated as MA 1,
though they were not able to isolate and characterize the particles. Manage et al . (1999) investigated
the seasonal changes in titres of cyanophages in Furuike Pond located in Sancho, Matsuyama City
(Japan). The titres of cyanophages infecting M . aeruginosa were at 2 x 10 2 and 4.2 x 10 4 PFU ml -1
during the months of June and September, respectively and this coincided with a decrease in the
population of the host cells from their initial densities of 1.8 x 10 4 and 9.4 x 10 5 cells ml -1 in the
corresponding months. During winter season, however, the cyanophages were not detectable and the
host was represented at low levels. Honjo et al . (2006) studied the diversity of virus-like agents killing