GENOMES - Cyanobacteria - page 127

necessary for the transport and utilization of urea, cyanate and oligopeptides have been identifi ed in
P . marinus MED4 but with no transporters for amino acid uptake. P. marinus MIT9313 has transporters
for urea, amino acids and oligopeptides but lacks the genes necessary for cyanate utilization. In
both the genomes, genes required for ammonia transport ( amt1 ) and its incorporation through
GS-GOGAT pathway are present besides the gene ( ntcA ) that encodes the nitrogen transcriptional
regulator. A high affi nity phosphate transport system encoded by pstS and pstABC is present in the
genomes of both the strains with an additional copy of the phosphate-binding component pstS for
utilization of orthophosphate from deeper waters. P. marinus MED4 possesses P-related regulatory
genes ( phoB and phoR -two component system and the transcriptional activator ptrA ) whereas this
system seems to be non-functional in P. marinus MIT9313 as it is interrupted by two frame-shifts
and further degeneration noted in ptrA . The presence of genes encoding fl avodoxin ( isiB ) in both
P . marinus MED4 and MIT9313 has been demonstrated. An Fe-induced transcriptional regulator
in both strains include ( Fur that represses iron uptake genes) and numerous genes involved in
high-affi nity iron scavenging system and absence of genes concerned with Fe-siderophore complex
are the additional characteristics of the iron acquisition system (Rocap et al ., 2003). These iron-related
genes are absent in Synechococcus sp. strain WH8102 and this explains its dominance in iron-limited
equatorial Pacifi c. In the genome of Synechococcus sp. strain WH8102, 5 to 6% of the gene complement
is devoted for transport phenomena. Nearly 60% of the ORFs encode ABC- transporters. P-type
ATPase transporter is found with only one transporter for copper. The uptake of urea and phosphate
is facilitated by the synthesis of solute-binding proteins. For deriving nitrogen, the transporters
for amino acids and oligopeptides are present. This strain is additionally equipped with genes for
cyanate utilization as a source of nitrogen. In the marine waters, phosphonates (compounds with
C-P bonds) produced by eukaryotic phytoplanktons (Coccolithophorids of Chrysophyta) constitute
alternative P-source. So Synechococcus sp. strain WH8102 is equipped with genes for transport
of phosphonates and the presence of genes for multiple phosphatases ( SYNW0120 , SYNW0196 ,
SYNW2391 and SYNW2390 ) explains the ability to obtain P from such environments. The presence
of effl ux transporters in the ABC family and effl ux pumps for metals ( SYNW1472 and SYNW0900 ),
chromate ( SYNW1323 ) and arsenite ( SYNW1039 ) are the additional features (Palenik et al ., 2003).
Synechococcus sp. strain CC9311 is an inhabitant of coastal environment and thus is adapted to grow in
higher phosphate concentrations. Accordingly, this strain lacks genes for a phosphate sensor-response
regulator commonly seen in other cyanobacteria. In addition, it lacks several alkaline phosphatases
that are present in Synechococcus sp. WH8102, which is an inhabitant of the open oceans. Metal
transporters like FeOA/B transporter for iron that is absent in Synechococcus sp. strain WH8102 is seen
in the coastal Synechococcus sp. strain CC9311 to meet the higher concentrations of iron in the coastal
environment. In order to adjust to the osmotic changes in the coastal environment, Synechococcus sp.
strain CC9311 is equipped with a metallothionein gene ( SmtA ) and fi ve and two mechanosensitive ion
channels of the type MseS and MseL , respectively compared with only two of MesS in Synechococcus
sp. strain WH8102 (Palenik et al ., 2006). In M . aeruginosa NIES-843 synthesis of proteins required for
phosphate acquisition is regulated by a two component system Hik7 (SphS) and Rre29 (SphR) that
regulates the expression of genes, i.e. ABC-type of phosphate transporter. Three operons that encode
subunits for ABC-type phosphate transporters (MAE18310-MAE18280, MAE18380-MAE18340 and
MAE09280-MAE09250), three monocistronic genes for phosphate-binding periplasmic proteins
(MAE18390, MAE32380, MAE38290) and two genes for alkaline phosphatases (MAE50240 and
MAE16640) are present in the genome of this cyanobacterium (Kaneko et al ., 2007).