Cyanobacteria sp. (diazotrophic and planktonic) hold a major position in ecosystem, former one due to their intrinsic capability of N2-fixation and later because of mineralization of organic matter. Unfortunately, their exposure to variety of abiotic stresses is unavoidable. Comparative analysis of interactive effect of UV-B and heavy metals (Cd/Zn) on nitrogen and phosphorus metabolism of three cyanobacteria (Anabaena, Microcystis, Nostoc) revealed additive inhibition (χ(2) significant p < 0.05) of NH4(+) and PO4(3-) uptake whereas increase in nitrate uptake upon UV-B + heavy metal exposure. Glutamine synthetase and Alkaline phosphatase activity was reduced after all treatments whereas Nitrate reductase activity showed slight stimulation in UV-B and UV-B + heavy metals treatment. Combination of UV-B and metals seems more detrimental to the NH4(+), PO4(3-) uptake, GS and APA activity. A significant stimulation in NO3(-) uptake and NR activity following exposure to UV-B in all the three cyanobacteria suggests UV-B-induced structural change(s) in the enzyme/carriers. Metals seem to compete for the binding sites of the enzymes and carriers; as noticed for Anabaena and Microcystis showing change in Km while no change in the Km value of Nostoc suggests non-competitive nutrient uptake. Higher accumulation and more adverse effect on Na(+) and K(+) efflux proposes Cd as more toxic compared to Zn.
In recent years, release of chemical pollutants has increased due to anthropogenic activities. Heterocystous filamentous cyanobacteria constitute dominant paddy microflora and are excellent biofertilizers augmenting rice productivity. Cyanobacteria are frequently exposed to toxic metals, nickel and arsenic are one of the major toxicants present. We exposed two species of diazotrophic cyanobacteria Anabaena sp. PCC 7120 and Anabaena doliolum, to sub-lethal concentrations (15.0 and 9.0 μM) of Ni and (17.0 and 11 mM) of arsenite (AsIII) and analyzed at different days of treatments (0, 1, 7, and 15 days) for oxidative damage and antioxidative biomarkers. Lipid peroxidation was enhanced (1.5- to 2.5-fold increase in MDA content), indicating damaging effects of Ni and As(III) on membrane. Although Ni and As(III), both induced oxidative stress in both species, Anabaena PCC 7120 experienced less stress than A. doliolum. This could be explained by a higher activity of antioxidant enzymes catalase (CAT), ascorbate peroxidase (APX), glutathione reductase (GR) in Anabaena PCC 7120 (4.6-, 2.0- and 1.4-fold [Ni ] 3.2-, 2.5-, and 2.08-fold [As]) compared to A. doliolum (4.2-, 2.5-, and 1.3-fold [Ni ] and 3.2-, 3.33-, and 1.8-fold [As]). Moreover, superoxide dismutase registered less inhibition in Anabaena sp. PCC 7120 (1.5 and 1.8) compared to A. doliolum (1.8 and 2.3) under Ni and As(III) stress. In addition to, IBR revealed that As(III) imposes severe impact on both strain, however, A. doliolum suffers most. Therefore, the study demonstrates interspecies variation in survival strategy of two Anabaena species and difference in potential of two different toxicants to produce oxidative stress.
Ecological adaptation of organisms to environmental stresses including heavy metals denotes a novel example of evolution under extreme selection pressure. Cyanobacteria represent the largest and most diverse group of prokaryotes, capable of performing oxygenic photosynthesis and are frequently found in environments contaminated with heavy metals. Quite a lot of proteomic studies have investigated the effects of metals such as Cu, Co, Cd, and As(V) etc. on diazotrophic cyanobacteria. However, proteomic studies for the identification of proteins modulated Ni and arsenite [As(III)] have not been carried out. In the present work, we have analyzed the proteomic pattern alterations of the cyanobacterium Anabaena PCC7120 in response to Ni and As(III) in order to identify the metabolic processes affected by these metals. We found that some proteins are commonly regulated in response to the different metal, including ribulose1,5-bisphosphate carboxylase, chaperones and antioxidative defence proteins, whereas others such as specific efflux proteins, were specifically induced by each metal. Our results demonstrated that arsenite appears to be more toxic than nickel.
Cyanobacteria are photoautotrophic prokaryotes capable to grow in diverse ecological habitats, originated 2.5-3.5 billion years ago and were first to produce oxygen. Since then superoxide dismutases (SOD) acquired great significance due to their ability to catalyze detoxification of byproducts of oxygenic photosynthesis i.e. superoxide radicals. In the present study, we extracted information regarding SODs from species of sequenced cyanobacteria and investigated their diversity, conservation, domain structure, and evolution. 144 putative SOD homologs were identified. Unlike other protein families (ex. HIGHLIGHTS 144 putative SOD homologs were identified among 85 sequenced cyanobacterial genomes. Gene gain-and-loss is insignificant during SOD evolution as they lack additional domain. Increased transcript level under abiotic stress confirms their role in abiotic stress. Insert a highlight no longer than 85 characters. Insert a highlight no longer than 85 characters. HIGHLIGHTS • Insert 1-4 highlights no longer than 85 characters. • Insert a highlight no longer than 85 characters.
The comparative effects of nickel (Ni 2+ ) and arsenite (As(III)) on two diazotrophic cyanobacterial species were investigated in terms of photosynthetic attributes. Both metals demonstrated inhibitory effects on growth, pigments (chl a and phycocyanin) and photosystem II (PS II) photochemistry. However As(III) exerted severe effects as compared to Ni reflected by (1) reduced growth (2) significant inhibition of chl a and phycocyanin, (3) reduction in maximum photochemical efficiency of PSII and (4) depleted plastoquinone pool, thus suggesting it as more toxic. Moreover, comparative analysis of two species also demonstrated interspecies variation in terms of stress adaptive strategies reflected through higher sensitivity of Anabaena doliolum over Anabaena PCC7120. Thus the study recommends application of A. PCC7120 as biofertilizer in Ni and As(III) contaminated paddy fields.
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