Biology Reference
In-Depth Information
Falkowski (2008) as 200 and 682, respectively for
N
.
azollae
0708 and in this respect the endosymbiont
resembles the free-living
Nostoc
and
Anabaena
species in retaining the important copies of the genes
in both core and shell regions. However, it is quite apparent that the greater erosion in minimal set
of genes governing glycolysis (
pfkA
,
gapA
,
pykA
,
gpmA
,
ldh
), nucleic acid replication, recombination
and repair has taken place in the genome of the symbiont consistent with the needs of the host plant.
The presence a phosphoenolpyruvate-dependent sugar phosphotransferase system in
N
.
azollae
0708 akin to the major carbohydrate transport system in bacteria suggests that the cyanobacterium
receives the required carbohydrates from the host plant. In return, the host plant receives fi xed
nitrogen from the symbiont as the symbiont has lost few genes in the areas of amino acid transport
and metabolism, uptake of bicarbonate and phosphate and the ability to utilize alternative combined
nitrogen sources thus reducing the symbiont to a nitrogen fi xer.
xvi) Genome of N. punctiforme ATCC 29133
:
The genome (8.2 Mb) has a mol% G+C of 41.5 and
only 94% of the sequenced genome has been annotated and in this respect a preliminary analysis
revealed 6,086 protein-coding ORFs of which 5314 are associated with previously recognized ORFs.
The genes that encode proteins of known or probable function function are 3328 (amounting to 45%).
The genes that encode conserved hypothetical and hypothetical proteins of unkown function are
1986 (constituting 27% of the total). Genes that do not bear resemblance to the previously known
genes constitute 29% of the total. A comparison with
Anabaena
sp. strain PCC7120 genome revealed
that
N
.
punctiforme
ATCC 29133 possesses 4814 (86%) of the ORFs of
Anabaena
. However, the number
of ORFs of
N
.
punctiforme
in
Anabaena
is 5610 (Meeks
et al
., 2001).
III. CATEGORIES OF GENES
According to the principles laid down by Riley (1993) the putative genes, whose function is known
have been grouped into 14 categories. A comparative account of these groups is provided in
Table 5 for four genera, i.e.
Synechocystis
sp.strain PCC 6803,
G
.
violaceus
PCC 7421,
T
.
elongatus
BP-1
and
Anabaena
sp. strain PCC 7120. The number of genes in each category is more in
Anabaena
sp.
PCC 7120. It may be because of the fact that it is a nitrogen fi xer. So genes associated with heterocyst
differentiation and nitrogen fi xation are additionally present in this organism. Genes related to
regulatory functions are represented in large numbers in
Anabaena
sp. PCC 7120 (339) with minimum
being represented in
T
.
elongatus
BP-1 (87).
1) Biosynthesis of co-factors, prosthetic groups and carriers
:
Synechococcus
sp. strain WH8102
possesses genes for the synthesis of plastocyanin (copper) for photosynthetic electron transport
instead of ferredoxin and a cobalt-dependent ribonucleotide reductase (governed by
SYNW1692
;
rather than iron-containing one as noted in many cyanobacteria) to overcome the iron defi ciency.
Genes for iron-dependent metalloenzymes (cytochrome P450 two additional cytochrome
c
molecules
and one or two additional ferredoxins) are present in
Synechococcus
sp. strain CC9311 (Palenik
et al
.,
2006). Nicotinamide adenine dinucleotide (NAD) participates in a number of metabolic and regulatory
processes. NAD(P) co-factors assume signifi cance due to their role in photosynthesis and respiration.
Taking into account
Synechocystis
sp. strain PCC 6803 as a model organism, Gerdes
et al
. (2006)
compared the genomes
of
E
.
coli
K12MG1655 and twelve other cyanobacteria (
A
.
variabilis
ATCC 29413,
N
.
punctiforme
PCC 73102,
Anabaena
sp. strain PCC 7120,
S
.
elongatus
PCC 7942,
P
.
marinus
MIT9313,
P
.
marinus
subsp.
marinus
strain CCMP1375 (MED4),
P
.
marinus
subsp.
pastoris
strain CCMP1986,
Synechococcus
sp. strain WH8102,
T
.
erythraeum
IMS101,
T
.
elongatus
BP-1,
C
.
watsonii
WH8501,
G
.
violaceus
PCC 7421). In all the cyanobacterial genomes examined including the model organism,
