A large gene cluster encoding peptide synthetases and polyketide synthases is involved in production of siderophores and oxidative stress response in the cyanobacterium Anabaena sp. strain PCC 7120.

Non-ribosomal peptide synthetases (NRPSs) and polyketide synthases (PKSs) are necessary for the production of a variety of secondary metabolites, such as siderophores involved in iron acquisition. In response to iron limitation, the cyanobacterium Anabaena sp. strain PCC 7120 synthesizes several siderophores.

The PsaE subunit of photosystem I prevents light-induced formation of reduced oxygen species in the cyanobacterium Synechocystis sp. PCC 6803.

The PsaE protein is located at the reducing side of photosystem I (PSI) and is involved in docking the soluble electron acceptors, particularly ferredoxin. However, deletion of the psaE gene in the cyanobacterium Synechocystis sp. strain PCC 6803 inhibited neither photoautotrophic growth, nor in vivo linear and cyclic electron flows.

PrpJ, a PP2C-type protein phosphatase located on the plasma membrane, is involved in heterocyst maturation in the cyanobacterium Anabaena sp. PCC 7120.

Protein phosphatases play important roles in the regulation of cell growth, division and differentiation. The cyanobacterium Anabaena PCC 7120 is able to differentiate heterocysts specialized in nitrogen fixation. To protect the nitrogenase from inactivation by oxygen, heterocyst envelope possesses a layer of polysaccharide and a layer of glycolipids.

PrxQ-A, a member of the peroxiredoxin Q family, plays a major role in defense against oxidative stress in the cyanobacterium Anabaena sp. strain PCC7120.

The genome of the cyanobacterium Anabaena PCC 7120 encodes seven polypeptides showing sequence similarities with peroxiredoxins (Prx-s). One of them, prxQ-A (alr2503), which encodes a Prx Q homologue, is located in the same gene cluster as pkn22, which encodes a Ser/Thr kinase. Here we report that the pkn22-knockout mutant (Mp22) is sensitive to oxidative stress because it fails to synthesize PrxQ-A; the expression of prxQ-A is significantly induced under oxidative stress conditions.

Inhibition of cell division suppresses heterocyst development in Anabaena sp. strain PCC 7120.

When the filamentous cyanobacterium Anabaena PCC 7120 is exposed to combined nitrogen starvation, 5 to 10% of the cells along each filament at semiregular intervals differentiate into heterocysts specialized in nitrogen fixation. Heterocysts are terminally differentiated cells in which the major cell division protein FtsZ is undetectable. In this report, we provide molecular evidence indicating that cell division is necessary for heterocyst development.

Iron starvation leads to oxidative stress in Anabaena sp. strain PCC 7120.

We establish here that iron deficiency causes oxidative stress in the cyanobacterium Anabaena sp. strain PCC 7120. Iron starvation leads to a significant increase in reactive oxygen species, whose effect can be abolished by treatment with the antioxidant tempol (4-hydroxy-2,2,6,6-tetramethylpiperidine 1-oxyl).

Open reading frame ssr2016 is required for antimycin A-sensitive photosystem I-driven cyclic electron flow in the cyanobacterium Synechocystis sp. PCC 6803.

Open reading frame ssr2016 encodes a protein with substantial sequence similarities to PGR5 identified as a component of the antimycin A-sensitive ferredoxin:plastoquinone reductase (FQR) in PSI cyclic photophosphorylation in Arabidopsis thaliana. We studied cyclic electron flow in Synechocystis sp. PCC 6803 in vivo in ssr2016 deletion mutants generated either in a wild-type background or in a ndhB deletion mutant.

The chlorophyll-binding protein IsiA is inducible by high light and protects the cyanobacterium Synechocystis PCC6803 from photooxidative stress.

The products of the isiAB operon are a chlorophyll antenna protein (IsiA) and flavodoxin (IsiB), which accumulate in cyanobacteria grown under iron starvation conditions. Here we show that strong light triggers de-repression of isiAB transcription and leads to IsiA and flavodoxin accumulation under iron replete conditions. Genetic deletion of isiAB resulted in a photosensitive phenotype, with accumulation of reactive oxygen species and cell bleaching in high light, while the flavodoxin-deficient isiB null mutant expressing isiA was phototolerant.

pkn22 (alr2502) encoding a putative Ser/Thr kinase in the cyanobacterium Anabaena sp. PCC 7120 is induced by both iron starvation and oxidative stress and regulates the expression of isiA.

In cyanobacteria, the isiA gene is required for cell adaptation to oxidative damage caused by the absence of iron. We show here that a putative Ser/Thr kinase gene, pkn22 (alr2052), is activated by iron deficiency and oxidative damage in Anabaena sp. PCC 7120.

A photosystem 1 psaFJ-null mutant of the cyanobacterium Synechocystis PCC 6803 expresses the isiAB operon under iron replete conditions.

A psaFJ-null mutant of Synechocystis sp. strain PCC 6803 was characterised. As opposed to similar mutants in chloroplasts of green algae, electron transfer from plastocyanin to photosystem 1 was not affected.

Hypothesis: versatile function of ferredoxin-NADP+ reductase in cyanobacteria provides regulation for transient photosystem I-driven cyclic electron flow.

Pseudo-reversion of the high-CO2 requiring phenotype of the NADH dehydrogenase type 1-impaired mutant of Synechocystis PCC6803, strain M55, by salt stress coincides with partial restoration of PSI-driven cyclic electron transfer. In M55, the complete family of D proteins (D1-D6) that are needed for electron transfer through the complex is lacking. Adaptation to salt stress requires de novo synthesis of full-length 47-kDa ferredoxin-NADP reductase (FNR).