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Abstract
In recent years the process of accumulation of heavy metal
ions by microorganisms was intensely studied. Micro organisms
like bacteria, yeast and fungi, as well as algae can accumulate
large amounts of heavy metal ions.
Biosorption is considered to be a fast physical or chemical
recovery process. The biosorption rate depends on the type of
the process. According to literature, biosorption can be divided
into two main processes: adsorption of the ions on cell surface
and bioaccumulation within the cell.
The bioaccumulation of heavy metals is closely related
with their toxicity, i.e. restraining microorganisms metabolism
and growth. Low concentrations of heavy metal ions are
necessary for the vitality of all microbial cells and certain low
concentrations of Cu and Zn even stimulate the growth and the
activity of the metabolic processes. The values of the critical
and threshold concentrations depend on the type of the microorganism
and the properties of the metal. The metal toxicity is
affected also by the form in which they exist in the medium, the
amount of cells in the medium and the stage of growth of the
cell culture.