Tolypothrix tenuis stress response to nickel

Abstract

Metal ions are both essential and potentially toxic. The aim of this work was to demonstrate that diazotrophic cyanobacterium Tolypothrix tenuis Nº54 can tolerate toxic concentrations of Ni2+ in order to use the biomass in biofilters or as biofertilizer. For this purpose, growth, pigment and protein contents and catalase activity of T. tenuis growing in increasing concentrations of Ni2+ ranging from 10-10 to 10-4 M were assesed. The strain did not grow at Ni2+ concentration of 10-4 M, but at lower concentrations there were no significant differences with the control; it was tolerant at 10-10 and 10-8 M. Nickel concentration of 10-6 M is toxic for this cyanobacterial strain, because dry weight decreased by 30%; allophycocyanin and phycoerythrin decreased by 92% and 98%, respectively and protein content increased by 42%. Chlorophyll a concentration was more than double the control value in 10-10 and 10-8 M, but in 10-6 M it decreased by 19%. Catalase (E.C. 1.11.1.6) activity doubled the control value in the lowest nickel concentration whereas in 10-8 M there was no significant difference with the control and in 10-6, it decreased by 78%. The living biomass of this strain could be used as a step in the bioremediation process in waters contaminated with concentrations of nickel lower than 10-6 M and eventually as a biofertilizer.