Katarzyna Hrynkiewicz, Christel Baum
Department of Microbiology, Institute of Biology and Environmental Protection, Nicolaus Copernicus University, Torun, Poland.
Heavy metals are important environmental pollutants which belong to the group of non-biodegradable and persistent compounds deposited in plant tissue (e.g. vegetables) which are then consumed by animals and humans. Increased pollution of natural environment with heavy metals, particularly in areas with anthropogenic pressure, also contributes to disorders in the natural balance of microbial populations. Molecular analysis carried out during the past decades revealed that density and diversity of microorganisms significantly correlated with increased contamination of the environment with heavy metals. As a result, a selective promotion of metal-tolerant genera of microorganisms was observed. In general, microorganisms are organisms with relatively high tolerance of unfavourable conditions, and these properties evolved over millions of years. In this chapter, a variety of mechanisms responsible for adaptation of microorganisms to high heavy metal concentrations, e.g. metal sorption, uptake and accumulation, extracellular precipitation and enzymatic oxidation or reduction, will be reported. Moreover, molecular mechanisms responsible for their metal tolerance will be described. The efficiency of accumulation of heavy metals in the microbial cells will be discussed and presented in photos from a reflection electron microscope (REM). The capacities of microorganisms for metal accumulation can be exploited to remove, concentrate and recover metals from polluted sites. This provides the basis for biotechnological solutions for the remediation of contaminated environments. Bioremediation has been regarded as an environment-friendly, inexpensive and efficient means of environmental restoration. Since microorganisms constitute a key factor of this technology, knowledge of the nature and molecular mechanisms of their tolerance of increased heavy metal concentrations is essential.