Influence of light quality on extracellular ammonium excretion by cyanobacteria isolated from Loktak Lake, the only largest freshwater lake in the North-Eastern region of India

Cyanobacteria experience changes in light quantity and light quality in their natural habitat. In response to changes in light quality, they re-distribute excitation energy and adjust photosystem stoichiometry to maximize the utilization of available light energy. In the present study, six (06) cyanobacterial strains namely, Nostoc sp. BTA60, Nostoc sp. BTA61, Nostoc commune BTA67, Calothrix sp. BTA73, Nostoc sp. BTA80 and Nostoc muscorum BTA950 were cultured under different qualities of light modes (white, blue, green and red) to ascertain on the excretion of extracellular ammonium. Among the four light qualities used, white light was found to be most effective followed by red, green and blue light in all the strains tested. Nostoc muscorum BTA950 released maximum extracellular ammonium (236.98 μgml-1) in white light followed by red light (231.77 μgml-1), green light (225.17 μgml-1) and blue light (220.18 μgml-1). Nostoc sp. BTA80 released minimum extracellular ammonium in white light (103.29 μgml-1) and all other light conditions (red, green and blue). The present findings suggest that Nostoc muscorum BTA950 could be used for commercial production of ammonium when grown under white light. These strains were found to be useful for their utilization in agriculture and industry