Identification of factors regulating the Cu2+ efflux in copper tolerant (Cur) strain of Nostoc calcicola

Abstract

Copper is a well known micronutrient, an algaecide, metal component of

thylakoidal plastocyanin and superoxidase dismutase. The Cu

2+ efflux is the

sole mechanism responsible to develop copper tolerance in

Nostoc calcicola.

Copper tolerant/ resistant (Cu

r) strain showed time dependent (0â€60 min)

Cu

2+ efflux whereas no efflux was reported in the Cu sensitive (Cus) N. calcicola

cells. The Cu

2+ efflux depends on the presence of photogenic ATP while

it is inhibited around 95% in the dark growing cells. The ATP, supplied externally

to these cells could restore 50% cations efflux compared to no improvement

in light growing cells which suggests that the photosynthetically generated

energy in later case was optimum to drive Cu

2+ efflux. Metabolic inhibitors

such as mercaptothanol, azide, N, N’

â€dicyclohexylcarbodimide and pâ€

Chloromercuribenzoate inhibit the metal efflux at different level. Cu

2+ efflux

in the Cu

r strain initiated only for 100â€fold lower Cu concentration in the external

medium (0.6

μM Cu). The Cu2+ efflux rate for 1000â€fold diluted set at 1

h suggested that higher dilution or the lower amounts of Cu (0.06

μM) offered

regulation for the efflux event. These findings suggested the use of Cu

r

strain in bioleaching program for metal removal in repetitive cycles without

any measurable loss.