Nostoc

The cyanobacterial genus Nostoc includes several species forming centimetre-large gelatinous colonies in nutrient-poor freshwaters and harsh semi-terrestrial environments with extended drought or freezing. These Nostoc species have filaments with normal photosynthetic cells and N2-fixing heterocysts embedded in an extensive gelatinous matrix of polysaccharides and many other organic substances providing biological and environmental protection. Large colony size imposes constraints on the use of external resources and the gelatinous matrix represents extra costs and reduced growth rates. The objective of this review is to evaluate the mechanisms behind the low rates of growth and mortality, protection against environmental hazards and the persistence and longevity of gelatinous Nostoc colonies, and their ability to economize with highly limiting resources. Simple models predict the decline in uptake of dissolved inorganic carbon (DIC) and a decline in the growth rate of spherical fre...

Bacteriophytochromes sense light in the near-infrared window, the spectral region where absorption by mammalian tissues is minimal, and their chromophore, biliverdin IXα, is naturally present in animal cells. These properties make bacteriophytochromes particularly attractive for optogenetic applications. However, the lack of understanding of how light-induced conformational changes control output activities has hindered engineering of bacteriophytochrome-based optogenetic tools. Many bacteriophytochromes function as homodimeric enzymes, in which light-induced conformational changes are transferred via α-helical linkers to the rigid output domains. We hypothesized that heterologous output domains requiring homodimerization can be fused to the photosensory modules of bacteriophytochromes to generate light-activated fusions. Here, we tested this hypothesis by engineering adenylate cyclases regulated by light in the near-infrared spectral window using the photosensory module of the Rhod...

We report secondary structure assignments for the cyanobacteriochrome NpF2164g3 in the violet-absorbing dark-adapted state. Comparison with our previous work on the orange-absorbing photoproduct elucidates structural changes occurring upon photoconversion.

The light-harvesting phycobilisome in cyanobacteria and red algae requires the lyase-catalyzed chromophorylation of phycobiliproteins. There are three functionally distinct lyase families known. The heterodimeric E/F type is specific for attaching bilins covalently to α-subunits of phycocyanins and phycoerythrins. Unlike other lyases, the lyase also has chromophore-detaching activity. A subclass of the E/F-type lyases is, furthermore, capable of chemically modifying the chromophore. Although these enzymes were characterized >25 y ago, their structures remained unknown. We determined the crystal structure of the heterodimer of CpcE/F from Nostoc sp. PCC7120 at 1.89-Å resolution. Both subunits are twisted, crescent-shaped α-solenoid structures. CpcE has 15 and CpcF 10 helices. The inner (concave) layer of CpcE (helices h2, 4, 6, 8, 10, 12, and 14) and the outer (convex) layer of CpcF (h16, 18, 20, 22, and 24) form a cavity into which the phycocyanobilin chromophore can be modeled. ...

In the case of nitrogenase-based photobiological hydrogen production systems of cyanobacteria, the inactivation of uptake hydrogenase (Hup) leads to significant increases in hydrogen production activity. However, the high-level-activity stage of the Hup mutants lasts only a few tens of hours under air, a circumstance which seems to be caused by sufficient amounts of combined nitrogen supplied by active nitrogenase. The catalytic FeMo cofactor of nitrogenase binds homocitrate, which is required for efficient nitrogen fixation. It was reported previously that the nitrogenase from the homocitrate synthase gene (nifV) disruption mutant of Klebsiella pneumoniae shows decreased nitrogen fixation activity and increased hydrogen production activity under N2. The cyanobacterium Nostoc sp. strain PCC 7120 has two homocitrate synthase genes, nifV1 and nifV2, and with the ΔhupL variant of Nostoc sp. strain PCC 7120 as the parental strain, we have constructed two single mutants, the ΔhupL ΔnifV1...

Human activity is causing depletion of ozone in stratosphere, resulting in increased UV-B radiation and global warming. However, impact of these climatic changes on the aquatic organism (especially marine) is not fully understood. Here, we have studied the effect of excess UV-B and visible radiation on photosynthetic pigments, fatty acids content, lipid peroxidation, nitrogen content, nitrogen reductase activity and membrane proteins, induction of mycosporine-like amino acids (MAAs) and antioxidant enzymes superoxide dismutase (SOD) and ascorbate peroxidase (APX) in freshwater (Nostoc spongiaeform) and marine (Phormidium corium) cyanobacteria. UV-B treatment resulted in an increase in photosynthetic pigments in Nostoc and decrease in Phormidium, but high light treatment caused photobleaching of most of the pigments in both the species. Unsaturation level of fatty acids of both total and glycolipids remained unchanged in both the cyanobacteria, as a result of UV-B and high light trea...