Emergence of toxic cyanobacterial species in the Ganga River, India, due to excessive nutrient loading

Despite of several efforts by the Government of India, pollution in National River Ganga is rising. The aim of the present study is to investigate the pollution in Ganga River in relation to appearance of toxic cyanobacterial strains. Jajmau area of Kanpur city is the industrial hub of Uttar Pradesh and is the main source of adding unwanted discharge into Ganga River. Water samples were randomly collected from the most polluted stretch of Ganga River (Kanpur, Uttar Pradesh, India). Samples were also collected from other major water of Uttar Pradesh to compare their water chemistry with Ganga River. Physico-chemical parameters of water bodies were estimated periodically for three years 2013-2015. Pearson product-mean correlation showed strong correlation between water parameters of sampling sites. Regression analysis showed seasonal variation in water parameters of Ganga River. Cyanobacteria prevalence in Ganga River was highest in May while lowest in August month. Fourteen cultivable cyanobacteria were isolated from Ganga River. Two new isolates, Oscillatoria sp. RBD01 and Leptolyngbya sp. RBD05 were found to be toxic and showed the presence of algal toxin (microcystin). Phylogenetic relatedness of toxic cyanobacterial isolates with their close homologues was established using 16S rRNA sequence analysis. Microcystin content in water samples (extracellular release) and in cyanobacterial isolates (intracellular content) was estimated by enzyme linked immunosorbent assay. Ganga River was found to be positive for microcystin with concentration ≥2 ppb which is above the permissible limit of WHO. Toxic cyanobacteria Oscillatoria sp. RBD01 and Leptolyngbya sp. RBD05 showed the presence of 23 and 17 ppb of microcystin in cells. Growth of the toxic cyanobacteria Oscillatoria sp. RBD01 showed very strong correlation with phosphate (0.834) and nitrate (0.761) content of water. Toxic Oscillatoria sp. RBD01 growing in moderate combination of nitrate (16x) and phosphate (4x) showed optimum growth and protein content. Periodic assessment of water quality and monitoring of toxic cyanobacteria would be helpful in identification and regulation of toxins which are responsible for destroying its sanctity and making it unsafe for human consumption.