CYANOPHAGES - Cyanobacteria - page 441

Table 8: Cyanophages isolated a on PE and PC-containing strains of Synechococcus b and the strains on which cross-infection
was possible (after Lu et al ., 2001).

Cyanophage(s) Host strain on which isolated Strains on which cross-infection was

possible

P2, P39, P53, P56, P71, P72, P73, P79, P81,
P82 and P83

PE-containing strain WH 7805 PE-containing strains WH 7803 and WH

8108

P3 PE-containing strain WH 7805 Majority of PE- and PC-containing strains

P5 and P16 PE-containing strain WH 7803 Majority of PE- and PC-containing strains

P8 and P14 PC-containing strain WH 8101 PE-containing strains WH 7803 and WH

7805

P12 PC-containing strain WH 8101 Did not cross-infect on any other strain

P68 PC-containing strain WH 8007 PC-containing strain WH 8101

P76 PC-containing strain WH 8007 Did not cross-infect on any other strain

a From the Georgia coastal river (Savannah, Altamaha and Satilla) estuaries.
b Four PE-containing strains (WH7803, WH 7805, WH 8103 and WH 8108) and seven PC-containing strains (WH 8101, WH
8007, WH 5701, CCMP 1628, CCMP 1629, CCMP 1630 and CCMP 1632) of Synechococcus have been used by Lu et al . (2001)
in this study. PE-Phycoerythrin; PC-Phycocyanin

cyanophages that were isolated from different depths and locations. The diversity of phages was
represented by all the three groups of tailed phages. Cyanomyoviruses are quite unique in having
a broader host range as they not only infected and cross-infected Prochlorococcus strains among each
other but also did so between Prochlorococcus and Synechococcus strains. Those cyanophages isolated
on Synechococcus exhibited broader host range as they infected low-light (LL-) adapted strains of
Prochlorococcus as well. This was explained on the basis that the LL-adapted Prochlorococcus strains
are less diverged from Synechococcus and they in fact are closely related with each other on the basis
of rDNA sequence homology. But none of these phage strains have infected marine bacterial isolates.
Cyanosiphoviruses have been represented by two cyanophages (P-SS1 and P-SS2) that were specifi c
to their respective hosts. In contrast, cyanopodoviruses were extremely host-specifi c with ony two
cross infections out of a possible 300. High light-(HL-) adapted strains of Prochlorococcus are wide
spread in marine waters and these supported the multiplication of cyanopodoviruses that have a
restricted host-range. Titres of cyanophages infecting strains of Synechococcus were relatively high
(10 6 phages ml -1 ) when compared to those sensitizing Prochlorococcus strains. Certain of the strains
of Prochlorococcus (MIT 9303, MIT 9313 and SS120) had low or no cyanophage strains infecting
them while on other hosts the cyanophage titres were generally lower (350 phages ml -1 ) (Table 9).
However, representatives of cyanophages infecting the respective Prochlorococcus strains could be
found to depths of 70 m to 100 m. These studies were extended to include surface coastal waters
(mesotrophic) to open ocean sites (oligotrophic) of the Atlantic Ocean in relation to the natural
abundance of the respective host strains. Nearly 98% representative morphotypes of cyanophages
infecting HL-adapted Prochlorococcus were of cyanopodoviruses while the rest were cyanomyoviruses.
LL-adapted Prochlorococcus strains were infected by cyanomyoviruses (65%) and the rest belonged to
cyanopodoviruses. On the other hand, maximum infection of Synechococcus was by cyanomyoviruses
(93%) and the rest belonged to the other two categories.
A similar study conducted by McDaniel et al . (2006) at the Gulf of Mexico led to the characterization
of 35 marine cyanophages isolated on Synechococcus sp. strain WH7803 as the host. Morphologically,
94% of these were found to be myoviruses and the rest of them belonged to podovirus category. The
cross infectivity of these strains was tested on 24 strains of Synechococcus isolated from the surface
waters and extending up to a depth of 75 m. Some of the cyanophages (SPGM-01, SPGM-02 and