10.22376/ijpbs.2019.10.1.p1-12 Volume 7 Issue 4 2016 (October - December) The growing incorporation of nanomaterials and excessive heavy metal discharge into the environment calls for the better understanding of their toxicological effects on the ecosystem. For analyzing their toxic effects we have chosen cyanobacteria as our model system. Cyanobacteria is known to accumulate heavy metals and act as a sink for many aquatic contaminants. The present study aims towards screening of four cyanobacterial strains namely lessThan i greaterThan Synechococcus sp lessThan /i greaterThan ., lessThan i greaterThan Scytonema sp lessThan /i greaterThan ., lessThan i greaterThan Nostoc lessThan /i greaterThan lessThan i greaterThan muscorum lessThan /i greaterThan and lessThan i greaterThan Plectonema boryanum lessThan /i greaterThan , against silver stress. Our results indicated that out of four strains, two strains namely lessThan i greaterThan Nostoc muscorum lessThan /i greaterThan and lessThan i greaterThan Plectonema boryanum lessThan /i greaterThan were found to be less sensitive while lessThan i greaterThan Scytonema sp lessThan /i greaterThan . exhibited highest sensitivity towards Ag stress. Our results state that the growth inhibition of cyanobacterial strains is in the order of lessThan i greaterThan Scytonema sp greaterThan Synechococcus sp greaterThan Nostoc muscorum greaterThan Plectonema boryanum lessThan /i greaterThan which was estimated in terms of photosynthetic pigment (Chl a). Effect of Ag stress on carotenoids (Car) and total protein was also studied. Based on the above results, the less sensitive strains namely lessThan i greaterThan Nostoc muscorum lessThan /i greaterThan and lessThan i greaterThan Plectonema boryanum lessThan /i greaterThan were further studied against silver nanoparticles stress. All experiments were repeated three times to ascertain the reproducibility of the results. Values are represented as mean ± SE. Thus, the understanding of the responses incurred in cyanobacteria during heavy metal and metal nanoparticle stress can be very well used to evaluate their toxic responses in the environment. SADAF MAHFOOZ, ZAIRISH IMRAN, ADEEBA SHAMIM AND ALVINA FAROOQUI Cyanobacteria, heavy metals, silver, silver nanoparticles 60-70