Externally supplied ascorbic acid moderates detrimental effects of UV-C exposure in cyanobacteria.

The defensive role performed by exogenously supplied ascorbic acid in the cyanobacterium Nostoc muscorum Meg1 against damages produced by UV-C radiation exposure was assessed in this study. Exposure to UV-C (24 mJ/cm2) significantly enhanced reactive oxygen species (ROS) (50%) along with peroxidation of lipids (21%) and protein oxidation (22%) in the organism. But, addition of 0.5 mM ascorbic acid prior to UV-C exposure showed reduction in ROS production (1.7%) and damages to lipids and proteins (1.5 and 2%, respectively). Light and transmission electron microscopic studies revealed that ascorbic acid not only protected filament breakage but also restricted severe ultrastructural changes and cellular damages in the organism. Although the growth of the organism was repressed up to 9% under UV-C treatment within 15 days, a pre-treatment with ascorbic acid led to growth enhancement by 42% in the same period. Various growth parameters such as photo-absorbing pigments (phycoerythrin, phycocyanin, allophycocyanin, chlorophyll a, and carotenoids), water splitting complex (WSC), D1 protein, RuBisCO, glutamine synthetase and nitrogenase activities in the UV-C treated organism were seen to be relatively intact in the presence of ascorbic acid. Thus, a detailed analysis undertaken in the present study was able to demonstrate that ascorbic acid not only act as first responder against harmful UV-C radiation by down-regulating ROS production, it also accelerated the growth performance in the organism in the post UV-C incubation period as an immediate response to an adverse experience presented in the form of UV-C radiation exposure.

Nostoc muscorum is a novel source of microalgal lectins with potent antiviral activity against herpes simplex type-1.

In our survey for a new antiviral agent, two types of lectin were purified from Nostoc muscorum using both ion-exchange and affinity columns chromatography. Nostoc muscorum lectins (NMLs) are categorized based on their carbohydrate preference. Nostoc muscorum lectin-1(NML-1) exhibited a strict binding specificity for complex glycoproteins without linked carbohydrates, and the other displayed specificity for α- glycosides mannose polymers (NML-2) and was classified as a glycoprotein with 16.8% linked carbohydrates. NML-1 displayed a single band of 166 kDa on native-PAGE and two bands of 81 kDa and 85 kDa on SDS-PAGE, which confirmed the heterodimeric nature of this lectin. While NML-2 is a 50 kDa glycoprotein composed of 25 kDa subunits. Physical characterization of NML-1 displayed its stability at a higher temperature of 90 °C for 5 min and over a wide pH range (4-9), while MNL-2 displayed stability up to a temperature of 80 °C for 25 min and a pH range of 5-8. NML-1 didn't require metal ions for agglutination activity, while the activity of NML-2 was doubled by manganese ions. The antiviral activity of two lectins was assessed against herpes simplex type-1 (HSV-1) using a plaque assay which revealed that NML-1 inhibited HSV-1 infection at an early stage in contrast to NML-2 which exerted its antiviral effect at the late stage of infection. These results suggest that Nostoc muscorum is a unique lead for antiviral drug discovery as it is a novel source for antiviral lectins with different modes of action.

NaCl-induced physiological and biochemical changes in two cyanobacteria Nostoc muscorum and Phormidium foveolarum acclimatized to different photosynthetically active radiation.

The present study is aimed at investigating physiological and biochemical behavior of two cyanobacteria Nostoc muscorum and Phormidium foveolarum acclimatized to different levels (sub-optimum; 25 ± 0.5, optimum; 75 ± 2.5 and supra-optimum; 225 ± 3.5 µmol photons m(-2) s(-1)) of photosynthetic active radiation (PAR), and subsequently treated with two doses (30 and 90 mM) of NaCl. PAR influences growth in tested cyanobacteria being maximum in supra-optimum PAR acclimatized cells. NaCl-induced maximum percent decline in growth was observed in sub-optimum PAR acclimatized cells, which was in consonance with a decrease in chlorophyll content. Sub-optimum PAR acclimatization stimulated phycocyanin content in control cells, whereas maximum carotenoids content was observed in supra-optimum PAR acclimatized cells. Photosystem II photochemistry viz. Fv/F0, Fv/Fm, Ψ0, ϕE0, PIABS, ABS/RC, TR0/RC, ET0/RC and DI0/RC was also influenced by PAR and NaCl. Maximum percent rise in superoxide radical (SOR), hydrogen peroxide (H2O2) and lipid peroxidation was observed in sub-optimum PAR acclimatized cells exposed to NaCl, which could be correlated with lower values of enzymatic (superoxide dismutase, catalase, peroxidase and glutathione-S-transferase) and non-enzymatic (NP-SH and cysteine) antioxidants. In supra-optimum PAR acclimatized cells level of oxidative stress markers was in parallel with enhanced antioxidants. The results suggest that PAR significantly changes physiological and biochemical responses of studied cyanobacteria under NaCl stress. Besides this, this study also shows that P. foveolarum is more tolerant than N. muscorum under test conditions.

Heavy metal removal from multicomponent system by the cyanobacterium Nostoc muscorum: kinetics and interaction study.

In this study, Nostoc muscorum, a native cyanobacterial species isolated from a coal mining site, was employed to remove Cu(II), Zn(II), Pb(II) and Cd(II) from aqueous solution containing these metals in the mixture. In this multicomponent study, carried out as per the statistically valid Plackett-Burman design of experiments, the results revealed a maximum removal of both Pb(II) (96.3 %) and Cu(II) (96.42 %) followed by Cd(II) (80.04 %) and Zn(II) (71.3 %) at the end of the 60-h culture period. Further, the removal of these metals was attributed to both passive biosorption and accumulation by the actively growing N. muscorum biomass. Besides, the specific removal rate of these metals by N. muscorum was negatively correlated to its specific growth rate. For a better understanding of the effect of these metals on each other's removal by the cyanobacteria, the results were statistically analyzed in the form of analysis of variance (ANOVA) and Student's t test. ANOVA of the metal bioremoval revealed that the main (individual) effect due to the metals was highly significant (P value <0.05) on each other's removal. Student's t test results revealed that both Zn(II) and Pb(II) strongly inhibited both Cu(II) removal (P value <0.01) and Cd(II) removal (P value <0.02). All these results not only demonstrated a very good potential of the cyanobacteria in the bioremoval of these metals but also the effect of individual metals on each other's removal in the multicomponent system.

Identification and quantification of microcystins from a Nostoc muscorum bloom occurring in Oukaïmeden River (High-Atlas mountains of Marrakech, Morocco).

Health risks generated by cyanobacterial toxins in drinking and recreational waters are clearly recognised. During the monitoring programme on the distribution of toxic freshwater cyanobacteria in various water bodies including reservoirs, ponds and rivers of Morocco, many toxigenic cyanobacteria bloom-forming species have been identified. Particular attention was given to the investigation of the toxicology of a benthic Nostoc species-Nostoc muscorum Ag. (cyanobacteria, Nostocales, Nostocaceae)-that was found dominant in Oukaïmeden river located at 2,600 m of altitude in High-Atlas mountains of Marrakech. The massive growth of the mat-forming N. muscorum occurred yearly during the period of March-October, when the water temperature was above 10 degrees C. During 1997-1999, samples were collected from either floating or benthic mats. Hepatotoxicity associated to gastrointestinal (diarrhoea) intoxication symptoms was confirmed by intraperitoneal (i.p.) injection in mice of N. muscorum thallus extract. The survival time was estimated to be from 2-5 h, and the calculated i.p. LD(50) in mice ranged from 15 to 125 mg kg(-1) body weight. The application of the high performance liquid chromatography with photodiode array detection confirmed the occurrence of microcystin-LR (MC-LR) and three others microcystin variants from the methanolic Nostoc extract. The MC-LR represented a proportion of 39% of the total microcystin content however, the total concentration equivalents-eq-of MC-LR was estimated to be 139 microg MC-LR eq per gram dry weight. The existence of a benthic microcystin-producing N. muscorum strain under the particular environmental conditions of Oukaïmeden region may be a potential human health hazard and the ecological harmful effects of these cyanobacterial toxins need to be assessed. This paper constitutes the first report of the occurrence of a toxic benthic Nostoc in Morocco. So, the benthic species should be considered during monitoring of toxic Cyanobacteria particularly for river used for source of drinking water.

Sorption and desorption studies of chromium(VI) from nonviable cyanobacterium Nostoc muscorum biomass.

This communication presents results pertaining to the sorptive and desorptive studies carried out on chromium(VI) removal onto nonviable freshwater cyanobacterium (Nostoc muscorum) biomass. Influence of varying the conditions for removal of chromium(VI), such as the pH of aqueous solution, the dosage of biosorbent, the contact time with the biosorbent, the temperature for the removal of chromium, the effect of light metal ions and the adsorption-desorption studies were investigated. Sorption interaction of chromium on to cyanobacterial species obeyed both the first and the second-order rate equation and the experimental data showed good fit with both the Langmuir and freundlich adsorption isotherm models. The maximum adsorption capacity was 22.92 mg/g at 25 degrees C and pH 3.0. The adsorption process was endothermic and the values of thermodynamic parameters of the process were calculated. Various properties of the cyanobacterium, as adsorbent, explored in the characterization part were chemical composition of the adsorbent, surface area calculation by BET method and surface functionality by FTIR. Sorption-desorption of chromium into inorganic solutions and distilled water were observed and this indicated the biosorbent could be regenerated using 0.1 M HNO3 and EDTA with upto 80% recovery. The biosorbents were reused in five biosorption-desorption cycles without a significant loss in biosorption capacity. Thus, this study demonstrated that the cyanobacterial biomass N. muscorum could be used as an efficient biosorbent for the treatment of chromium(VI) bearing wastewater.

Studies on poly-beta-hydroxybutyrate synthase activity of Nostoc muscorum.

This study compares the PHB synthase activity of Nostoc muscorum, a N(2)-fixing cyanobacterium under control (grown in usual BG-11 medium), nitrogen (N) and phosphorus (P) deprivation and chemoheterotrophic conditions. Specific activity of PHB synthase did not depict significant variations in the latter three types of cultures, except for the control one, where a significantly lower activity was recorded. PHB synthase activity was detected only in the soluble fractions of both the control as well as cells incubated under chemoheterotrophic conditions. A K(m) of 80.2 microM DL-beta-hydroxybutyryl-CoA and V(max) of 197.5 nmol thiobenzoate (TNB) mg protein(-1)min(-1) were observed for the enzyme. PHB synthase remained insensitive to acetyl-CoA, ATP, NADP, NADPH supplementation under in vitro condition. Addition of acetyl phosphate was found to activate the enzyme and the level of activation was dependent on the concentration of acetyl phosphate supplementation. Inhibition of PHB synthase in 2,3-butanedione supplemented cultures and reactivation following acetyl phosphate addition proved the post-translational control of acetyl phosphate over PHB synthase.