Biology Reference
In-Depth Information
belonging to photosynthetic, housekeeing and cyanobacteria-specifi c genes. Among these, 938 genes
are represented in this category in
A
.
platensis
. COGs specifi c for
A
.
platensis
are 1066 among which
2056 genes are present. Of these, 71 are common to group (iv) and group (v) recognized by them.
Among the heterocystous members 223 gene clusters are common to them. Signifi cant features of
the genome of
A
.
platensis
are (i) 150 group II introns (amounting to 612 kb) are present of which 71
of them are responsible for reverse transcriptase/maturases, (ii) presence of as many as 22 adenyl
cyclases of which 10 are membrane associated signal transduction proteins, (iii) two-component
signal transduction systems comprise of 84 putative histidine kinases of which 33 encode hybrid
histidine kinases and 65 putative genes for response regulators, (iv) additionally methyl-accepting
chemoreceptor proteins (8 genes), Ser/Thr protein kinases (43 genes), response regulators (20 genes)
with an N-terminal receiver domain and helix-turn-helix DNA-binding C-terminal region are present,
(v) 66 putative genes for σ
70
type transcription factors are represented. Another remarkable feature of
the genome is the presence of genes for heterocyst differentiation (
hetU
,
hetR
and
hetF
) and nitrogen
fi xation while at the same time no nitrogenase genes are present. Likewise, genes for type IV pilus
that confer twitching motility are present but with no obvious twitching motility. Comparative
genomic analysis revealed seven COG clusters for fi lamentous organization including
Synechococcus
sp. strain PCC 7002, seven genes of which are present in the genome of
A
.
platensis
. That is why
Synechococcus
sp. strain PCC 7002 has been projected as a primitive fi lamentous type and included
as the sole representative of group (iii) by Fujisawa
et al
. (2010).
b) Genome of Arthrospira
sp
. PCC 8005
: Whole genome shotgun sequencing with pyrosequencer
technology assisted by MaGe automated annotation brought out important features of the genome of
Arthrospira
sp. PCC 8005 (Janssen
et al
., 2010). The genome (with 6,279,260 bases) has a G+C content
of 44.7% and 5,856 protein-coding sequences and comes closer to the genomes of
Arthrospira maxima
CS-328 and
Lynbya
PCC 8106 in showing highest overall synteny. There are 176 genes encoding RNAs.
Among the unique coding sequences mention may be made of (i) desaturases that are required for
production of β-carotene and two important fatty acids linoleic acid and γ-linolenic acid; (ii) for
utilizing nitriles as sole source of nitrogen (
nthPAB
) and (iii) a bidirectional hydrogenase
(hox
and
hyp
genes). The genome contains highly repetitive sequences of tandem repeats, short palindromic
repeats and insertion elements (Janssen
et al
., 2010).
xi) Genome of L. majuscula 3L
:
The
draft genome of
L
.
majuscula
3L has been published with partial
annotation of genes governing secondary metabolite production, DNA replication, recombination
and repair, cell wall biogenesis and signal transduction mechanisms (Jones
et al
., 2011). The size
of the genome (~8.5 Mb) comes closer to the genomes of
N
.
punctiforme
(8.2 Mb) and
T
.
erythraeum
(7.8 Mb). With a mol % G+C of 44, the genome has 7,479 protein-coding genes and this again is higher
than the number of genes found in
N
.
punctiforme
(6,086 genes) and
T
.
erythraeum
(4,451 genes). There
are two rRNA operons and 56 tRNAs. Most of the housekeeping genes (102) found in bacteria have
been identifi ed (101 genes) in
L
.
majuscula
3L. The largest cluster of COGs identifi ed belong to DNA
replication, recombination and repair (9%) followed by those of cell wall biogenesis (8%) and signal
transduction mechanisms (7%). When compared to the diversity of natural products produced by
this organism, the number of genes identifi ed (126 genes) appear to be low. Of these, 44% have been
assigned to non-ribosomal peptide synthetase- and/or polyketide synthase related genes. There
are eight clusters of genes assigned to the probable synthesis of natural products of which two of
them encode curacin A (an anticancer agent and tubulin polymerization inhibitor) and barbamide
(molluscicide). The genome of
L
.
majuscula
3L contains 15 genes assigned to the synthesis of sigma
factors. Type I and type II σ
70
factors Sig A to Sig E, respectively are encoded by fi ve genes each. The
