Relevance of Alkaline Phosphatase activity of immobilized green algae and cyanobacteria for heavy metal toxicity monitoring

Harmful effects of contaminants on the ecosystem and humans cannot be assessed by standard chemical analyses of environmental samples, therefore toxicity tests using live organisms or cells represent a vital part of environmental monitoring. Biological methods based on microorganisms as test-species, have already successfully been applied to environmental toxicity/genotoxicity assessment. The enzyme activity is examined in presence of essential and non-essential heavy metals (Ni, Zn, Cd) in green algae and cyanobacteria. The activity is based on total p-nitrophenol formed in a known volume of culture suspension. The activity was deleteriously affected in a concentration dependent manner. The maximum Apase activity observed in immobilized state of A.nidulans was 14.6 n moles pNP ^g protein-1 per 30 minutes in presence of non-inhibitory level of Ni and Cd. The effect due to interaction between different variables (cell state type, metal type and metal dose) depicted a significant variation (P< 0.01, ANOVA) in the Apase activity of free and immobilized cells of S. quadricauda and A. nidulans. This study describes the alkaline phosphatase activity which may differ with metal type, cell type or metal dose of the solution. Immobilization may protect the cell enzyme activity against the toxicity of heavy metals. The study may help in designing biosensor when estimating heavy metals quantitatively.