Potentially toxic metals (PTM) that are accumulating in soil represent a threat to organisms, including human. The problem of increased contents of PTM in soil is that they do not degrade, hence they resist in the environment in contrast to some other contaminants. When estimating their harmfulness toward organisms, their bioavailability is more important than their total content. Bioavailability is dependent on the arrangement of metals between solid and liquid soil fraction, that is defined by the interactions between metals and the solid part of a soil matrix. These interactions depend on the physico-chemical characteristics of the soil and biological processes included in transport of PTM into the cell. Some bacteria have adapted to the contaminated environment, so that they can convert PTM to less toxic forms or change their bioavailability. They do that using different mechanisms of resistance that are encoded on resistance genes on chromosome, plasmids or transposons. Among most studied mechanism are: reduced uptake from the environment, increased secretion by the efflux pumps, extracellular sequestration, intracellular sequestration and chemical modification of PTM. It is well known that contamination with PTM can provoke so called co-selection process, leading to the selection of bacteria that exhibit resistance to PTM as well as to antibiotics. The trait of bacteria to be able to live in the environment with increased PTM contents could be used in environmental biotechnology, for bioremediation. For now researchers have only shown this potential under laboratory conditions. For the promotion of phytoremediation are especially useful PTM resistant plant growth promoting bacteria (PGPB), among which are found endophytic bacteria and rhyzobacteria. This work includes an literature overview of bacterial resistance to increased PTM contents in soil and their potential use in biotechnology.
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