Zn(II) and Cu(II) removal byNostoc muscorum: a cyanobacterium isolated from a coal mining pit in Chiehruphi, Meghalaya, India

Abstract

Nostoc muscorum was isolated from a coal mining pit in Chiehruphi, Meghalaya, India, and its potential to remove Zn(II) and Cu(II) from media and the various biochemical alterations it undergoes during metal stress were studied. Metal uptake measured as a function of the ions removed by N. muscorum from media supplemented independently with 20 μmol/L ZnSO4and CuSO4established the ability of this cyanobacterium to remove 66% of Zn2+and 71% of Cu2+within 24 h of contact time. Metal binding on the cell surface was found to be the primary mode of uptake, followed by internalization. Within 7 days of contact, Zn2+and Cu2+mediated dissimilar effects on the organism. For instance, although chlorophyll a synthesis was increased by 12% in Zn2+-treated cells, it was reduced by 26% in Cu2+-treated cells. Total protein content remained unaltered in Zn2+-supplemented medium; however, a 15% reduction was noticed upon Cu2+exposure. Copper enhanced both photosynthesis and respiration by 15% and 19%, respectively; in contrast, photosynthesis was unchanged and respiration dropped by 11% upon Zn2+treatment. Inoculum age also influenced metal removal ability. Experiments in the presence of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (a photosynthetic inhibitor), carbonyl cyanide m-chlorophenyl hydrazone (an uncoupler), and exogenous ATP established that metal uptake was energy dependent, and photosynthesis contributed significantly towards the energy pool required to mediate metal removals.