Uptake and speciation studies of radionuclides and heavy metals in boreal environmental microbiota (surface biosphere)
Soil microorganisms show impressive diversity and one of their most important features is their biochemical versatility.There are several processes found in soil microbiota, which affect the geochemical cycle of elements (figure on the bottom), including native biosorption, oxidation, reduction, enzymatic transformations, accumulation and precipitation. Oxidation-reduction processes are highly significant in the environment and are affected by microorganisms. Microorganisms can use several substances as an electron donor or as an electron acceptor. The most prevailing electron donor is by far organic carbon. When oxygen is not present, microorganisms can use alternative electron acceptors like nitrate, manganese, iron, arsenic or sulphur. In addition other oxyanions, like SeO32- or TcO4- can be used as electron acceptors . Various micro-organisms have also developed different metal resistance processes which include changes in the oxidation state of toxic metals like As(V), Ag(II) and Tc(VII).
Two types of cellular retardation processes, called bioaccumulation and biosorption, can be found in micro-organisms. Usually an active transport mechanism in which energy is required is referred as bioaccumulation and term biosorption is used when physical adsorption on cell membrane structures residing on the cell surfaces are employed. Intracellular accumulation is typically metabolism dependent and involves transportation of the substance through the cell membrane, a process which can be significantly affected by the presence of stable or radioactive ions.
In our group various retardation processes (uptake, protein structures involved in uptake, retardation, reduction, oxidation) of radionuclides (i.e. Tc, Np, Se, U, Ra) in soil bacteria isolated from boreal environment are studied.