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amplifi cation of a 150 bp fragment. Sequence analysis suggested that the 150 bp fragment matched
with N-terminal region of the MCP. As the sequence match confi rmed that it is MCP gene sequence,
a pair of new primers MCPF5 and MCPR5, were designed. A search of the database revealed that
there are no known sequences either at nucleotide level or protein level. MCP gene sequences from
viruses AN-15, N-1 and A-1(L) have been amplifi ed by PCR using MCPF5/R5 and PCR products
approximately 350 bp were obtained. Environmental samples of cyanophages from freshwater
lakes of United Kingdom (Priest Pot, Esthwaite Water and Burrate Reservoir) subjected to PCR
amplifi cation of MCP gene sequence revealed a total of 26 sequences that were almost identical. Based
on the differences at the nucleotide level in these sequences, these were grouped into 11 different
genotypes (A to K). Of these, A to F have been most frequently encountered. Genotypes identical
to that of AN-15 and A-1(L) have been detected in samples collected from Burrator Reservoir and
Esthwaite Water. Genotype A was found only in Priest Pot, an eutrophic pond. This constitutes the
fi rst report on the identifi cation of natural viral assemblages that infect fi lamentous cyanobacteria
inhabiting freshwater habitats. The generation of strongest PCR products from natural waters with
the sudden disappearance of the fi lamentous bloom-forming cyanobacterium at Esthwaite water
strongly suggests the involvement of cyanophages in controlling bloom populations. Wilhelm
et al
.
(2006) explained an interesting case relating to the occurrence of
g20
gene sequences in freshwaters
in the absence of a host. The distribution and diversity of cyanophages occurring in Lake Erie
has been studied by
g20
sequence analyses after PCR amplifi cation by primers CPS1 and CPS8
to amplify the region from ~826 to 1376 of the
g20
capsid assembly protein. The
g20
sequence
homologues present in the natural water samples as well as ballast of commercial ships were related
to marine cyanophages. It is signifi cant to note that the cyanophages present in the freshwaters of
this Laurentian Great Lake infected only the marine
Synechococcus
sp. strain WH7803 that is not an
inhabitant of these waters, out of a number of other strains (WH5701, WH8007, WH8101, WH8102,
PCC 7002, PCC 7942, PCC 6803 and BO 8807) of the same genus and
M
.
aeruginosa
LE3,
Microcystis
sp. UTEX 2386,
Anabaena
sp. UTEX 2558,
Anabaena
sp. UTEX 2576 and
Oscillatoria
luteus
tested for
host-range. It is suggested that the ships' ballast water may be responsible for the transfer of marine
cyanophages and other marine microbes that can survive their movement into freshwater. The
purifi ed cyanophage samples viewed through TEM revealed capsids with a mean diameter of 69.6
nm and a mean tail length of ~147.4 nm (Wilhelm
et al
., 2006). Thus ship's ballast water seems to be
an important conduit for the bioinvasion of microorganisms (of the order of 6.8 x 10
19
viruses and 3.9
x 10
18
bacterial cells per annum) at the Port of Hampton Roads in Lower Chesapeake Bay (Drake
et
al
., 2007). Employing CPS1 and CPS8 primers, the amplifi cation of
g20
sequences by PCR from the
fl ood waters of a Japanese paddy fi eld, Wang
et al
. (2010) found a great diversity in cyanophages
and several unique groups that were more closely related to those cyanophages from freshwaters
than to those from marine waters.
ii)
g23
: Genes
g18
to
g23
of phage T4 encode different proteins of the virion. Tail sheath (
g18
), tail
tube (
g19
), head portal protein (
g20
), prohead core protein (
g21
), a scaffold protein (
g22
) and the
major capsid protein (
g23
) are encoded by the respective genes mentioned in the parentheses.
Hambly
et al
. (2001) identifi ed conserved sequence in the genome of marine cyanophage S-PM2 that
is homologous to the gene sequences (
g18
to
g23
) of T4. In the conserved sequences of cyanophage
DNA, there are certain insertions and deletions of small ORFs of unknown function. The gene
sequences identifi ed relate to the structural components of the phage head and contractile tail. In
view of the structural differences in the morphology of these phages, considerable divergence in
amino acid sequence of the respective proteins may exceed uniformly by about 50%. Short fragments
(450 bp) of the gene encoding major capsid protein (
g23
) have been amplifi ed to assess the diversity
