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i.e.
dnaX
,
dnaN
,
holB
and
ssb
and DNA repair genes
recD
,
alkA
and
recQ
suggests that they are
functionally redundant. Though genes for biosynthesis of photosynthetic pigments, proteins of PSI
and PSII, nitrogen fi xation and heterocyst differentiation are well conserved, phylogenetic analysis
placed the genome of this organism (5.49 Mb) more closer to
C
.
raciborskii
CS-505 (3.88 Mb) and
R
.
brookii
D9 (3.19 Mb) rather than to the larger genomes of
Anabaena
sp. strain PCC 7120,
A
.
variabilis
ATCC 29413 and
Nostoc punctiforme
ATCC 73102 (Fig. 8). On the other hand,
N
.
azollae
0708 shares
highest number of COGs of proteins with
Anabaena
sp. strain PCC 7120,
A
.
variabilis
ATCC 29413 and
N
.
punctiforme
PCC 73102. In this respect, similar functional categories of COGs are shared in between
N
.
azollae
0708 and
N
.
punctiforme
PCC 73102 in signal transduction mechanisms, cell membrane
biogenesis, carbohydrate and amino acid metabolism and it is of special interest to know that the
pseudogenes are under represented in these categories of genes in
N
.
azollae
0708. Ran
et al
. (2010)
determined the “core” and “shell” gene sets identifi ed earlier for cyanobacterial genomes by Shi and
Lyrigbya
sp. PCC 8106
Arthrospria
maxima
CS-328
Trichodesmium
erythraeum
IMS 101
Raphidiopsis
brookii
D9
Cylindrospermopsis
raciborskii
CS 505
'
Nostoc
azollae
' 0708
Nostoc
sp. PCC 7120
Anabaena variabilis
ATCC 29413
Nostoc punctiforme
PCC 73102
Nodutaria spumigena
CCY9414
Figure 8:
Phylogenetic tree and genome sizes for ten fi lamentous cyanobacterial species. The closest relatives to '
Nostoc azollae
'
0708 are
Raphidiopsis brookii
D9 and
Cylindrospermopsis raciborskii
CS-505, the two multicellular cyanobacteria with the smallest
known genomes. The tree is a subclade from a maximum likelihood analysis of all cyanobacterial genomes available from
NCBI and IMG/ER. With the kind permission of B. Bergman, Department of Botany, Stockholm University, Stockholm, Sweden
[Ran
et al
. (2010)
PLoS ONE
5(7):
e11486. doi:10.1371/journal.pone.0011486] doi:10.1371/journal.pone.0011486.g002.
