Department of Biological Sciences

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End date: 2009Subject: search.filters.subject.Cyanobacterium

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Now showing 1 - 9 of 9
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    Copper uptake by free and immobilized cyanobacterium
    (OUP, 1989) Verma, Sanjay Kumar
    Copper uptake in free and immobilized cells of the cyanobacterium Nostoc calcicola has been examined. The immobilized cells invariably maintained a higher profile of Cu intake rate (12.7 nmol mg−1 protein min−1) over the free cells (6.0 nmol mg−1 protein min−1). The total Cu uptake in immobilized cells was almost two and a half-times more than their free cell counterpart under identical experimental conditions. Also, the immobilized cells showed a stronger positive correlation between Cu adsorption and uptake. The results have been discussed in terms of improved metabolic efficiency of immobilized cells.
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    Evidence for energy-dependent copper efflux as a mechanism of Cu2+ resistance in the cyanobacterium Nostoc calcicola
    (OUP, 1991) Verma, Sanjay Kumar
    Wild-type Nostoc calcicola carried out oxygenic photosynthesis extremely sensitive to copper. A Cu(2+)-resistant mutant (Cu-R1) of the cyanobacterium grew normally at high concentrations of Cu2+. Its ability to grow under such conditions was found to be due to mutational acquisition of an energy-dependent efficient system of Cu(2+)-efflux, which rendered Cu(2+)-inhibited oxygenic photosynthesis fully reversible.
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    pH regulation of growth, photosynthesis, glutamine synthetase activity and micronutrient transport in the cyanobacterium Hapalosiphon welwitschii
    (OUP, 1992) Verma, Sanjay Kumar
    Optima for growth, oxygenic photosynthesis and glutamine synthetase activity occurred at pH 10, thus suggesting that the cyanobacterium Hapalosiphon welwitschii is an alkalophile. It produced a Cu-Zn efflux system at pH 9 or 10, but not at pH 7 or 8, to relieve photosynthesis from Cu or Zn inhibition. This finding has a bearing on the ecophysiological competence of the cyanobacterium under natural conditions.
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    Multiple metal resistance in the cyanobacterium Nostoc muscorum
    (Springer, 1995) Verma, Sanjay Kumar
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    Co2+, Cu2+, and Zn2+ Accumulation by Cyanobacterium Spirulina platensis
    (Wiley, 2008) Verma, Sanjay Kumar
    The Spirulina platensis biomass was characterized for its metal accumulation as a function of pH, external metal concentration, equilibrium isotherms, kinetics, effect of co-ions under free (living cells, lyophilized, and oven-dried) and immobilized (Ca-alginate and polyacrylamide gel) conditions. The maximum metal biosorption by S. platensis biomass was observed at pH 6.0 with free and immobilized biomass. The studies on equilibrium isotherm experiments showed highest maximum metal loading by living cells (181.0 ± 13.1 mg Co2+/g, 272.1 ± 29.4 mg Cu2+/g and 250.3 ± 26.4 mg Zn2+/g) followed by lyophilized (79.7 ± 9.6 mg Co2+/g, 250.0 ± 22.4 mg Cu2+/g and 111.2 ± 9.8 mg Zn2+/g) and oven-dried (25.9 ± 1.9 mg Co2+/g, 160.0 ± 14.2 mg Cu2+/g and 35.1 ± 2.7 mg Zn2+/g) biomass of S. platensis on a dry weight basis. The polyacrylamide gel (PAG) immobilization of lyophilized biomass found to be superior over Ca-alginate (Ca-Alg) and did not interfere with the S. platensis biomass biosorption capacity, yielding 25% of metal loading after PAG entrapment. The time-dependent metal biosorption in both the free and immobilized form revealed existence of two phases involving an initial rapid phase (which lasted for 1–2 min) contributing 63–77% of total biosorption, followed by a slower phase that continued for 2 h. The metal elution studies conducted using various reagents showed more than 90% elution with mineral acids, calcium salts, and Na2EDTA with free (lyophilized or oven-dried) as well as immobilized biomass. The experiments conducted to examine the suitability of PAG-immobilized S. platensis biomass over multiple cycles of Co2+, Cu2+, and Zn2+ sorption and elution showed that the same PAG cubes can be reused for at least seven cycles with high efficiency.
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    Protective role of certain chemicals against UV-B-induced damage in the nitrogen-fixing cyanobacterium, Nostoc muscorum.
    (Wiley, 2003) Jha, Prabhat N.
    Exposure of the N(2)-fixing cyanobacterium Anabaena BT2 to ultraviolet-B radiation (2.5 W m(-2)) for 30 min resulted in complete loss of nitrogenase activity but 100% cell killing occurred only after a 90-min exposure. Inactivation of nitrogenase activity was not specific to Anabaena BT2; other species also showed a similar effect. The time required for 100% killing and inactivation of nitrogenase activity differed in various species, and this difference may be ascribed to the presence of different levels of UV-B protection mechanisms in individual species. Inhibition of nitrogenase activity was immediate, since exposure of cultures to UV-B for as little as 5 min elicited some inhibition of activity. The activity of UV-B-inhibited nitrogenase did not recover upon transfer of exposed cells to fluorescent light, suggesting that the inhibition may be due to specific inactivation of the enzyme. By employment of inhibitors of protein synthesis and PS-II activity, it was demonstrated that restoration of nitrogenase activity in a UV-B-treated culture occurred by fresh synthesis of nitrogenase polypeptide. Our findings suggest that estimation of nitrogenase activity in diazotrophic species may be used as a marker enzyme for assessing the impact of UV-B radiation.