Biology Reference
In-Depth Information
Trichormus
strains were placed outside Cluster I which contained all planktic and fi ve benthic
Anabaena
as well as
Aphanizomenon
strains.
Restriction analysis of 16S-23S ITS region has been put to use for phylogenetic analysis of strains
of non-photosynthetic eubacterial genera (Navarro
et al
., 1992; Vinuesa
et al
., 1998), cyanobacteria
belonging to various orders (Lu
et al
., 1997) and among the genera of heterocystous cyanobacteria
(West and Adams, 1997). Iteman
et al
. (2002) determined the 16S rDNA sequences (
A. fl os-aquae
PCC 9302, PCC 9332,
Aph. fl os-aquae
PCC 7905,
Nodularia
PCC 9350,
Anabaenopsis
sp. PCC 9215
and
Cyanospira rippkae
PCC 9501) and the phylogenetic trees based on both ML and distance-based
methods yielded similar results. With the exception of
C. raciborskii
all the strains could be assigned
to fi ve clusters. Although 16S rRNA sequence comparisons justify generic assignments but this is
not suitable for resolving differences below the level of genus (Turner, 1997). But on the basis of 16S
rRNA sequence comparisons a close relationship existed between
Aphanizomenon
and toxic
Anabaena
strains from various geographical locations. The RFLP patterns of PCC strains studied by these
workers do not justify their generic separation into
Anabaena fl os-aquae
and
Aph. fl os-aquae
as has
been done on the basis of morphological grounds or 16S rDNA sequences. Some other workers also
found closer relationships between strains of
Anabaena
and
Aphanizomenon
based on 16S rDNA RFLP
studies (Lyra
et al
., 1997, 2001; Lehtimäki
et al
., 2000). Strains of
Nodularia
clustered with the strains
of
Anabaena
and
Aphanizomenon
based on sequences of 16S rDNA as well as RFLP studies presented
by Iteman
et al.
(2002) though the
Nodularia
strains found to group with strains of genus
Nostoc
(Lyra
et al
., 2000; Lehtimäki
et al
., 2000). Komárek and Komárkova (2006) suggested that on the basis of
close resemblances of planktonic
Anabaena
strains to those of
Aphanizomenon
based on molecular
phylogenetic analyses (Iteman
et al
., 2002; Gugger
et al
., 2002; Rajaniemi
et al
., 2005a,b; Willame
et al
., 2006) the generic name
Aphanizomenon
should be retained as the valid name for this large
polymorphic group consisting of all planktonic
Anabaena
and
Aphanizomenon
strains
.
But according
to combined morphological and molecular criteria, the group is so morphologically diversifi ed that
can be divisible into different generic units (
Aph
.
fl os-aquae
,
Aph
.
gracile
,
Aph
.
issatschenkoi
and
Aph
.
volzii
-sub-clusters) with 16S rDNA sequence similarity of about or less than 95%. These conclusions
derive support from the work of Wu
et al
. (2010) who conducted morphological identifi cation of 53
strains of
Aphanizomenon
from China and assigned them to three morphotypes, i.e.
Aph
.
fl os-aquae
,
Aph
.
gracile
and
Aph
.
issatschenkoi
. Phylogenetic analysis of the strains based on concatenated alignment
of 16S rDNA,
rbcLX
and
cpcBA-
IGS sequences led the recognition of three clades corresponding to
the three morphotypes.
ii)
Synechococcus
cluster: (Cluster II as per Wilmotte and Herdman, 2001):
Six strain clusters of
Synechococcus
have been defi ned by Waterbury and Rippka (1989) based primarily on differences in
G+C content (mol%) and habitat (freshwater and marine). These strain clusters represent provisional
genera and are designated as follows:
Cyanobacterium
cluster;
Synechococcus
cluster,
Cyanobium
cluster,
MC-A, MC-B and MC-C.
Synechococcus
isolates maintained at the Pasteur Collection Centre (PCC)
have been divided into fi ve clusters that do not correspond with the above six clusters. (Rippka
and Herdman, 1992). Cultured
Synechococcus
strains from Japanese lakes and those from PCC were
subjected to PCR amplifi cation and DNA sequencing of 16S rDNA and the
cpcBA
-
IGS
and the fl anking
regions by Robertson
et al
. (2001). A phylogenetic analysis of
Synechococcus
strains revealed seven
clusters that refl ected phycobilin content. One strain of
Synechococcus
(PCC 7902) that stands apart is
only loosely affi liated to cyanobacterial lineage where no other cyanobacterial sequences were found.
An additional cyanobacterial lineage is represented by two hotspring
Synechococcus
isolates (PCC 6716
and PCC 6717), with these
Synechococcus elongatus
(Toray) PCC 6301 and other strains are grouped
