Epigenetic Regulation of Nostoc punctiforme ATCC 29133 in Response to Nitrogen Availability

Here, we report the restriction modification system of Nostoc punctiforme ATCC 29133, along with its methylated genome sequence, under contrasting nitrate availability. Generated methylation profiles revealed increased methylation for key enzymes of assimilatory nitrate reduction, suggesting that Nostoc punctiforme employs DNA methylation to regulate its nitrogen metabolism.

Nostoc punctiforme uses the Common Symbiosis Pathway to colonize endophytically Oryza sativa

Symbiosis between cyanobacteria and plants is considered pivotal for biological nitrogen deposition in terrestrial ecosystems. Despite extensive knowledge of the ecology of plant-cyanobacterium symbioses, little is known about the molecular mechanisms involved in recognition between partners. Here, we conducted a quantitative sequential window acquisition of all theoretical fragment ion spectra mass spectrometry (SWATH-MS) pipeline to analyse protein changes in Oryza sativa and Nostoc punctiforme during early events of symbiosis. In O. sativa, differentially expressed proteins were linked to several biological functions, including signal transduction, defence-related proteins, flavonoid biosynthesis, and cell wall modification. N. punctiforme displayed increases in expression of proteins involved in signal transduction and cell wall remodelling, including 11 Nod-like proteins, thus revealing a Nod-dependent signalling mechanism. We also found impaired symbiosis in a N. punctiforme nodB mutant and in O. sativa sym mutants in the common symbiosis signalling pathway by confocal microscopy. Our findings reveal signalling pathways activated in the early stages of the N. punctiforme-O. sativa symbiosis. They involve the common symbiosis signalling pathway as occur as in other plant-microbe symbioses. This information may have long-term implications for sustainably improving agriculture through a greater understanding of the symbiotic process.

Comparative genomic insights into culturable symbiotic cyanobacteria from the water fern Azolla

Species of the floating, freshwater fern Azolla form a well-characterized symbiotic association with the non-culturable cyanobacterium Nostoc azollae, which fixes nitrogen for the plant. However, several cyanobacterial strains have over the years been isolated and cultured from Azolla from all over the world. The genomes of 10 of these strains were sequenced and compared with each other, with other symbiotic cyanobacterial strains, and with similar strains that were not isolated from a symbiotic association. The 10 strains fell into three distinct groups: six strains were nearly identical to the non-symbiotic strain, Nostoc ( Anabaena ) variabilis ATCC 29413; three were similar to the symbiotic strain, Nostoc punctiforme , and one, Nostoc sp. 2RC, was most similar to non-symbiotic strains of Nostoc linckia. However, Nostoc sp. 2RC was unusual because it has three sets of nitrogenase genes; it has complete gene clusters for two distinct Mo-nitrogenases and an alternative V-nitrogenase. Genes for Mo-nitrogenase, sugar transport, chemotaxis and pili characterized all the symbiotic strains. Several of the strains infected the liverwort Blasia, including N. variabilis ATCC 29413, which did not originate from Azolla but rather from a sewage pond. However, only Nostoc sp. 2RC, which produced highly motile hormogonia, was capable of high-frequency infection of Blasia. Thus, some of these strains, which grow readily in the laboratory, may be useful in establishing novel symbiotic associations with other plants.

Differential catalase activity and tolerance to hydrogen peroxide in the filamentous cyanobacteria Nostoc punctiforme ATCC 29113 and Anabaena sp. PCC 7120

Photoautotrophic cyanobacteria often confront hydrogen peroxide (H2O2), a reactive oxygen species potentially toxic to cells when present in sufficiently high concentrations. In this study, H2O2 tolerance ability of filamentous cyanobacteria Nostoc punctiforme ATCC 29133 (Nostoc 29133) and Anabaena sp. PCC 7120 (Anabaena 7120) was investigated. Nostoc 29133 was better able to tolerate H2O2-induced inhibition of chlorophyll a and photosystem II performance, as compared to Anabaena 7120. The intracellular hydroperoxide level (indicator of oxidative status) also did not exhibit as much a rise in Nostoc 29133, as it did in Anabaena 7120 after H2O2 treatment. Accordingly, Nostoc 29133 showed higher intrinsic constitutive catalase activity than Anabaena 7120 indicating that the superior tolerance of Nostoc 29133 stems from its higher ability to decompose H2O2. It is suggested that difference in H2O2 tolerance between closely related filamentous cyanobacteria, as is borne out by this study, may be taken into account for judicious selection and effective use of strains in biotechnology.

Early events of the endophytic symbiotic between Oryza sativa and Nostoc punctiforme involve the SYM pathway

Symbiosis between cyanobacteria and plants is considered pivotal for biological nitrogen deposition in terrestrial ecosystems. Despite the large knowledge in the ecology of plant-cyanobacteria symbioses, little is known about the molecular mechanisms involved in the crosstalk between partners. A SWATH-mass spectrometry has been used to analyse, at the same time, the differential proteome of Oryza sativa and Nostoc punctiforme during the first events of the symbiosis. N. punctiforme activates the expression of thousands of proteins involved in signal transduction and cell wall remodelling, as well as 11 Nod-like proteins that might be involved in the synthesis of cyanobacterial-specific Nod factors. In O. sativa the differential protein expression was connected to a plethora of biological functions including signal transduction, defense-related proteins, biosynthesis of flavonoids and cell wall modification. N. punctiforme symbiotic inspection of O. sativa mutants in the SYM pathway reveals the involvement of this ancestral symbiotic pathway in the symbiosis between the cyanobacterium and the plant.

Biotechnological Production of the Sunscreen Pigment Scytonemin in Cyanobacteria: Progress and Strategy

Scytonemin is a promising UV-screen and antioxidant small molecule with commercial value in cosmetics and medicine. It is solely biosynthesized in some cyanobacteria. Recently, its biosynthesis mechanism has been elucidated in the model cyanobacterium Nostoc punctiforme PCC 73102. The direct precursors for scytonemin biosynthesis are tryptophan and p-hydroxyphenylpyruvate, which are generated through the shikimate and aromatic amino acid biosynthesis pathway. More upstream substrates are the central carbon metabolism intermediates phosphoenolpyruvate and erythrose-4-phosphate. Thus, it is a long route to synthesize scytonemin from the fixed atmospheric CO2 in cyanobacteria. Metabolic engineering has risen as an important biotechnological means for achieving sustainable high-efficiency and high-yield target metabolites. In this review, we summarized the biochemical properties of this molecule, its biosynthetic gene clusters and transcriptional regulations, the associated carbon flux-driving progresses, and the host selection and biosynthetic strategies, with the aim to expand our understanding on engineering suitable cyanobacteria for cost-effective production of scytonemin in future practices.