Toxicity of Lead on Biochemical Changes of Nitrogen Fixing Cyanobacteria, Aulosira fertilissima Ghose

The study was aimed to evaluate biochemical fate of Aulosira fertilissima when treated with different doses of PbNO₃ which is the one of the sources of heavy metal of lead. Moreover, cyanobacteria, a group of prokaryotes, symbiotic, N₂ fixing organism, ubiquitous in distribution and used as a biofertilizer in the paddy fields. The heavy metals not only destroy organisms but also kill the non-target cyanobacteria in paddy fields. Therefore, in the current study an attempt has been made to study acute toxicity of PbNO₃ on biochemical changes like pigment contents, chlorophyll-a, b, total, phycobilins and carotenoids, metabolites- carbohydrates, proteins and phenols, and enzyme activity-protease and nitrate reductase of nitrogen fixing cyanobacteria Aulosira fertilissima Ghose when grown in BG11 media. Retardation of chlorophyll-a, b, total, phycobilin and carotenoids was observed in all the treatments of PbNO₃ when compared with control as the days progressed. On the other hand, metabolites like carbohydrates, proteins and phenols also showed decrease in their content after 96 hours treatment of different doses. However, the present study revealed that there is a rise in protein content in 6 ppm, and phenol content in 12.0 ppm and 22.0 ppm. Besides, there was an inhibition in the nitrate reductase and protease activities with an increase in PbNO₃ doses. Further, cyanobacterial species, Aulosira fertilissima could be considered for bioremediation processes due to their potentiality to tolerate up to 6.00 ppm of PbNO₃ dose without any adverse effect, but proper studies are necessary for their practical reuse and development of heavy metal resistant strains.