Biology Reference
In-Depth Information
Figure 10: Cytometric differentiation of virus-like particles
. Scatter plot of side scatter (SSC) versus green fl uorescence
(SYBR Green) showing 3 viral sub-populations: VLP1, VLP2 and VLP3. Sub-populations of virus-like particles (VLP) were
discriminated based on their differences in SYBR Green fl uorescence and SSC, as non-overlapping classes of size and green
fl uorescence according to Brussaard (2004). VLP1 and VLP2 correspond to populations observed previously in seawater
samples and described as bacteriophages (Marie
et al
., 1999). The sub-population VLP3 exhibited the same SYBR Green
fl uorescence level than VLP2 but was characterized by higher SSC. Recent work have indicated that viral population presenting
a cytometric signature similar to the one observed here for VLP3, were likely to be phytoplankton viruses (Buussard
et al
., 2005,
2008). With the kind permission of
M. Schapira, School of Biological Sciences, Flinders University, GPO Box 2100, Adelaide
SA 5001, Australia & Ifremer-LERN, Avenue du Général de Gaulle, 14520 Port en Bessin, France. [Schapira
et al.
(2010)
Saline
Systems
6:
2; doi:10.1186/1746-1448-6-2].
experiments (Bratbak
et al
., 1992; Heldal and Bratbak, 1991) and measurements of dissolved esterase
activity (Brussaard
et al
., 1995; van Boekel
et al
. 1992). These studies provided concentrations of
marine viruses ranging from 10
6
ml
-1
to 10
8
ml
-1
thus confi rming the earlier observations where the
marine viral concentrations ranged in between 10
7
ml
-1
to 10
8
ml
-1
for a variety of marine waters
(Bergh
et al
., 1989; Proctor and Fuhrman, 1990). A number of workers reported similar results from
several locations and depths.
b)
Molecular techniques
:
(i) T4 gene 20
: T4 gene20 (
g20
) encodes a protein, gp20 also known as portal
protein that is essential in the morphogenesis of phage head. It helps in the initiation of head assembly
by the formation of proximal vertex, for DNA packaging and for binding with the head-tail junction.
Sequence analysis of cyanophage genomes of S-PM2, S-WHM1 and S-BnM1 revealed a high degree of
similarity of a particular ORF. This ORF from these phages bears 36% identity to the T4
g20
sequence.
The ORF encodes a polypeptide of 550 amino acids long (Fuller
et al
., 1998). They employed two
cyanophage-specifi c (CPS) primers CPS-1 and CPS-2 to amplify the
g20
sequence by PCR from a
number of cyanophages belonging to the family Myoviridae previously isolated from different
geographical locations. They suggested that by employing the CPS-1 and CPS-2 primers it would be
