Biology Reference
In-Depth Information
96% respectively. The monophyletic nature of subsection V in
hetR
trees is consistent with 16S rRNA
phylogeny but not with analyses of
rbcL
,
nifH
and
nifD
phylogenies.
Wilmotte and Herdman (2001) considered that it is quite premature to treat taxonomy of
cyanobacteria on a phylogenetic basis. They further cautioned that due to two reasons the studies
on taxonomy and molecular phylogeny of cyanobacteria suffered a set back. The fi rst is that certain
strains of cyanobacteria investigated from culture collections have not been properly identifi ed
and secondly, the data on 16S rRNA sequences on some strains originated from morphologically
unidentifi ed members. That is why the identifi cation of a cyanobacterium on polyphasic approach
should be done fi rst before initiating studies on molecular phylogeny. Another important aspect
is to have as much ecological information as possible on cyanobacteria at the time of collection
and identifi cation on a polyphasic approach. For this would greatly help in the diversity assays of
cyanobacteria from different environments based on molecular markers and even if some sequences
have been identifi ed on the basis of culture independent approach, they can then be assigned to a
probable strain of close proximity based on the habitat. Wilmotte and Herdman (2001) have identifi ed
14 lineages or clusters in cyanobacteria by comparing 16S rRNA gene sequences and phylogenetic
relationships drawn on the basis of ML and NJ methods and bootstrap analysis involved 500
resamplings. These are as follows: (i) heterocystous cluster, (ii)
Prochlorococcus marinus
,
Synechococcus
,
Cyanobium
and the sequences from the Sargasso Sea; (iii)
Prochlorothrix hollandica
lineage, (iv) the
marine
Leptolyngbya
lineage, (v) freshwater “
Leptolyngbya
” lineage, (vi) the
Pseudoanabaena
cluster,
(vii) the halotolerant unicellular strains, (viii) the lineage of baeocyte-forming strains, (ix) the
Spirulina
cluster, (x)
Synechococcus
PCC 7002 and
Leptolyngbya fragile
PCC 7376 lineage, (xi) the
Synechocystis
PCC 6906-
Microcystis
lineage, (xii) the
Trichodesmium
-
Oscillatoria
PCC 7515 lineage, (xiii) the
Arthrospira
lineage and (xiv) the
Geitlerinema
lineage. Of these 14 clusters, cluster (vii) comprising the
halotolerant strains has been suggested to be quite unique that is based on a polyphasic approach.
Garcia-Pichel
et al
. (1998) compared the morphological, physiological features and 16S rRNA gene
sequences of unicellular, extremely halotolerant and moderately thermophilic cyanobacteria. All
these share a number of chemotaxonomic markers including phycobilins, carotenoids and possess
mycosporine-like amino acids as well. These are variable in their cell size and form colonies that exhibit
two planes of division and reproduce by baeocyte formation (strains MPI 96N303 and MPI 96N304).
Some are colonial but do not reproduce by baeocytes and cells divide in a single plane (MPI 96P402,
MPI 96P605, MPI 96AL03 and MPI 96AH13). Besides these,
Cyanothece
PCC 7418,
Dactylococcopsis
PCC
8305,
Aphanothece halophytica
ATCC 43922,
Cyanothece
MPI 95AH10 are also included in this analysis.
Taxonomically, all strains possibly belong to
Cyanothece
according to Castenholz and Waterbury (1989)
but
Aphanothece
or
Cyanothece
according to Anagnostidis and Komárek (1986). On the basis of NJ
phylogenetic tree analysis all these strains are placed in a monophyletic cluster. This is the fi rst group
of cyanobacteria that are closely related with each other on the basis of 16S rRNA gene sequencing
and a set of physiological characteristics. According to Wilmotte and Herdman (2001) this study 'is a
nice example of a polyphasic approach to the taxonomy of cyanobacteria'.
Seo and Yokota (2003) have drawn comprehensive phylogenetic relationships amongst
cyanobacteria (consisting of 3 strains of Chroococcales, 5 strains of Pleurocapsales, 7 strains of
Oscillatoriales, 7 strains of Nostocales and 2 strains of Stigonematales) based on 16S rRNA,
gyrB
(DNA gyrase subunit B),
rpoC1
(DNA-dependent RNA polymerase γ-subunit) and
rpoD1
(principal σ
factor of
E
.
coli
σ
70
type DNA-dependent RNA polymerase) gene sequences that revealed 5 subgroups
of cyanobacteria. They designed PCR primers for
gyrB
,
rpoC1
and
rpoD1
genes by using consensus
amino acid sequences registered in GenBank. Phylogenetic relationships drawn based on
gyrB
,
rpoC1
and
rpoD1
sequences supported 16S rRNA gene sequence based phylogeny. Phylogenetic trees
