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in 11 of the 12 waste stabilization ponds surveyed. Moreover, the dominant strains in these ponds
are reported to be not susceptible to LPP viruses. The incidence and magnitude of LPP-group
indicated that several ponds (Arkansas, California, Florida, Indiana, Missouri, South Dakota and
Texas) supported high cyanophage titres. New Hampshire pond failed to reveal the presence of the
virus. The distribution of cyanophages in fi sh-ponds of Israel and the prevalence of these phages in
high titre has been reported (Padan et al ., 1967; Padan and Shilo, 1969).
Shane (1971) surveyed the distribution of LPP-group of viruses in various types of natural waters
like rivers, streams, lakes, farms and residential ponds, oxidization and stabilization lagoons and
industrial storage waters. The virus was found during all seasons of the year and throughout a wide
range of pH. The virus was consistently absent from the headwaters of the three rivers. However,
the incidence of the virus was noted to increase when rivers fl owed through more populated areas.
So a relationship seems to exist between domestic and industrial pollution and with the ecology of
these viruses. Singh (1973) studied the occurrence and distribution of cyanophages in ponds, sewage
water and rice fi elds of Cuttack, India. Two types of cyanophages, i.e. clear plaque-forming (virulent)
and turbid plaque-forming (lysogenic) strains were observed in natural habitats. This constitutes
the fi rst report on the occurrence of cyanophages from the rice fi elds of India. Seasonal periodicity
of cyanophages AC-1, infecting A . nidulans ad C . minor , was studied by Sharma and Venkataraman
(1978). These workers selected three ponds, a waste stabilization pond each at IARI, New Delhi,
Nagpur (Maharashtra) and Ahmedabad (Gujarat) as well as freshwaters from River Ganges at
Haridwar (Uttarakhand). AC-1 has not been found at Nagpur and Ahmedabad or in Ganges water.
The cyanophage has been found in high titres in the ponds at New Delhi, which showed a maximum
in May-June, while it was lowest during winter (November to January).
Desjardins and Olson (1983) demonstrated some control of bloom concentrations of P .
boryanum in outdoor pond facilities with cyanophage LPP-1. This cyanophage was most effective
when present before the bloom developed indicating that cyanophages are likely to be useful in
preventing a cyanobacterial bloom rather than destroying a bloom already in progress. The different
degrees of genetic variability of cyanophages attacking cyanobacteria have been shown to be due
to degree of virus-induced inhibition of photoautotrophic energy metabolism and to the degree of
modifi cation of anabolic functions and subcellular structures of the cell (Mendzhul et al ., 1982). This
has further been experimentally substantiated by the distribution of cyanophages. The interaction
of the cyanophages LPP-1 and Aph-1 with their hosts, i.e. P . boryanum and Aphanothece stagnina ,
respectively in chemostat cultures revealed fl uctuations in number of host cells and phage particles
(Barnet et al ., 1981). The fl uctuation in the phage-host cell numbers has been shown to be due to
evolution of new phage-resistant strains of the hosts. PR-1 was resistant to LPP-DUN1 while it
was susceptible to a mutant phage. However, PR-2 was unaffected by this phage. PR-2 grew more
slowly than wild-type. Barnet et al . (1984) investigated the effect of suspended particulate material
on cyanophages-cyanobacteria interactions in liquid cultures. These studies revealed that (i) the
suspended silt protected cyanobacteria from lysis by the phage and (ii) the number of cyanophages
and host cells oscillated in a reciprocal manner.
Studies on ecological dynamics of the toxic bloom-forming cyanobacterium M . aeruginosa and
its cyanophages in Lake Mikata (Japan) have been made by the quantifi cation of phycocyanin
intergeneric spacer (PC-IGS) sequences in case of the former and the PCR amplifi cation of sheath
protein gene (g91) in case of the latter (Yoshida et al ., 2008). Simultaneously, the relative abundance
of microcystin-producing sub-population of the species of M . aeruginosa has been determined by
the amplifi cation of mcy gene. The population of M . aeruginosa was represented by two peaks as
refl ected by copies of PC-IGS sequences to maximum of 3 x 10 3 copies ml -1 in the month of May
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