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  • Author or Editor: B. Kaushik x
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Nitrogenase activity, ammonia excretion and glutamine synthetase (GS) activity were examined in five strains of Anabaena (A. anomala ARM 314, A. fertilissima ARM 742, A. variabilis ARM 310, A. oryzae ARM 313 and A. oryzae ARM 570) in the presence of 2.5 mM NO3-N (KNO3), 2.5 mM NH- 4-N [(NH4)2SO4] and diatomic nitrogen (N2). Ammonium-N was more inhibitory to nitrogenase activity as compared to NO3-N in all the strains. Maximum GS activity was exhibited in NO3-N medium, irrespective of the cyanobacterial strains studied. Uninduced release of ammonia was observed in all the species, with A. oryzae ARM 313 and Anabaena variabilis ARM 310 exhibiting maximum excretion of 0.25-0.31 and 0.27-1.23 m moles NH- 4 mg Chl-1 respectively on the 15th day of incubation. The glutamine synthetase activity of A. oryzae ARM 313 was relatively very high as compared to Anabaena variabilis ARM 310. There was no nitrate reductase activity in any of the Anabaena sp. grown on NH3-N or N2-N on the 15th day of incubation.

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The pigment accumulating potential of two strains of Anabaena was evaluated in the presence of various sugars (glucose, sucrose and jaggery), when incubated under light/darkness. Both strains exhibited excellent potential for phycocyanin (PC), phycoerythrin (PE) and total phycobiliproteins (PBS) production in light, in the presence of sugars. In terms of accumulation of % phycobiliproteins / proteins, Anabaena cylindrica (ATCC 29414) was observed to be more responsive to jaggery while sucrose and glucose were more stimulatory for Anabaena sp. (cyanobiont isolated from Azolla mexicana ). Significant enhancement in PC and PE content by supplementation with sugars emphasises the need for in-depth analysis of the interactions between assimilation of sugars and pigment production pathways in cyanobacteria.

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A wide variety of pigments, like chlorophyll, carotenoids and phycobiliproteins, which exhibit colours ranging from green, yellow, brown to red are present in algae. Increasing awareness of harmful effects of synthetic dyes and inclination of society towards the usage of natural products, such as plant / microbial based colours in food and cosmetics, has led to the exploitation of microalgae as a source of natural colours. Algal pigments have great commercial value as natural colorants in nutraceutical, cosmetics and pharmaceutical industry, besides their health benefits. Spirulina, Dunaliella capsules are now commonly prescribed health foods for improving vitality and longevity of human beings. This review describes the distribution, structure of these pigments in algae, with emphasis on specific techniques for extraction and purification, along with different methods of biomass production and commercially feasible techniques documented in literature. An overview of the industrial applications of these natural colouring agents in diagnostics, food and cosmetics industry is also provided.

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