Biology Reference
In-Depth Information
based on sequences of these genes and the combined amino acid sequences deduced from
rpoC1
and
rpoD1
suggested that LGT of rRNA might be suspected in case of
Synechocystis
sp. strain
PCC 6803.
The 24 cyanobacterial sequences have been resolved into fi ve clusters (A-E). Cluster A comprises
sequences from
Anabaena cylindrica
,
Anabaena variabilis
,
Anabaenopsis circularis
,
Chlorogloeopsis
sp.
PCC 6718,
Chroococcidiopsis
sp.,
Fischerella muscicola
and
Nodularia spumigena
. Cluster B consists of
Oscillatoria agardhii,
Oscillatoria nigro-viridis
,
Phormidium
sp. and
Spirulina platensis
while Cluster C
is composed of
Microcystis wesenbergii
NIES-104,
Pleurocapsa
sp. PCC 7327,
Pleurocapsa
sp.,
Stanieria
cyanosphaera
PCC 7437,
Synechocystis
sp. strain PCC 6803 and
Xenococcus
sp. Cluster D consists of
Pseudoanabaena
sp. PCC 7367,
Pseudoanabaena
sp. PCC 7403 and
Synechococcus
sp. PCC 7001. Cluster
E is represented by
Leptolyngbya
PCC 7375 and
Synechococcus leopoliensis
IAMM-6.
A number of studies have been devoted to resolve taxonomic disparities and also draw
phylogenetic relationships amongst different groups of cyanobacteria. Of the 14 clusters recognized
on the basis of 16S rRNA gene sequences in cyanobacteria (Wilmotte and Herdman, 2001), such
attempts were made with cyanobacteria belonging to six clusters. The taxonomic resolution of strains
of cluster I comprising of heterocystous members (
Anabaena
,
Aphanizomenon
,
Cylindrospermopsis,
planktic
Anabaena
,
Planktothrix
), cluster II of
Synechococcus
, cluster V of freshwater
Leptolyngbya
lineage, cluster VI of
Pseudoanabaena
, cluster XII of
Trichodesmium
-
Oscillatoria
PCC 7515 lineage and
cluster XIV of
Geitlerinema
lineage has been undertaken during recent years. These are summarized
below.
i) Heterocystous cyanobacterial cluster: (Cluster I as per Wilmotte and Herdman, 2001):
Studies
on the phylogeny of the heterocystous cyanobacteria based on 16S rRNA gene sequencing revealed
that these form a monophyletic cluster or group (Giovannoni
et al
., 1988; Turner, 1997; Wilmotte
and Herdman, 2001). Within this cluster, phylogenetic relationships of planktonic heterocystous
cyanobacteria based on the 16S rRNA gene sequence comparisons (Lyra
et al
., 1997; 2001; Barker
et
al
., 1999; Beltran and Neilan, 2000; Lehtimäki
et al
., 2000; Li
et al.
, 2000; Moffi t
et al
., 2001; Saker and
Neilan, 2001), DNA-dependent RNA polymerase gene (
rpoC1
; Fergusson and Saint, 2000; Wilson
et al
.,
2000), the intergenic spacer region of the phycocyanin operon (PC-IGS; Neilan
et al
., 1995; Baker
et al
.,
1999; 2000; Bolch
et
al
., 1999) and the IGS between two copies of the
gvpA
encoding major structural
gas vesicle protein (Barker
et al
., 1999) have been drawn.The extent of morphological diversity among
the planktonic heterocystous members has been depicted (Figs. 15, 16 and 17). Iteman
et al
. (2002)
reported the existence of fi ve monophyletic clusters among heterocystous cyanobacteria. Cluster 1
comprises forms assigned to
Anabaena
and
Aphanizomenon
. Cluster II comprises strains of
Anabaena
.
Cluster III is composed of
Anabaena circinalis
and
A
.
affi nis
(Beltran and Neilan, 2000). Cluster IV
and V possess planktonic and non-planktonic strains of
Nodularia
and
Cylindrospermopsis raciborskii
,
respectively. Although on the basis of morphological characateristics or heterocyst differentiation
patterns the members of the last two clusters can be identifi ed but 16S rRNA gene sequence similarity
is so high that all of them can be assigned to a single species. Alternatively, it can also be stated that
the resolving power of the 16S rRNA is not suffi cient enough to make a distinction of these members.
Keeping this in view, Iteman
et al
. (2002) compared the 16S rRNA gene sequences and the 16S rRNA-
23S rRNA ITS sequences of 11 planktonic members (
Anabaenopsis fl os
-
aquae
PCC 9302, PCC 9332,
PCC 9349, PCC 7905;
Anabaenopsis
sp. strains PCC 9215, PCC 9216, PCC 9608,
Anabaenopsis elenkinii
PCC 9420,
Cyanospira capsulata
PCC 9502,
Cyanospira rippkae
PCC 9501 and
Nodularia
sp. PCC 9350)
that formed a distinct subclade within the monophyletic clade of heterocystous cyanobacteria with
the exception of strains of
Cylindrospermopsis
. Five distinct phylogenetic clusters could be identifi ed
with in this subclade. Strains of
Anabaena
and
Aphanizomenon
are dispersed through three clusters