Taking nature into lab: biomineralization by heavy metal-resistant streptomycetes in soil
Biomineralization by heavy metal-resistant streptomycetes was tested to evaluate the potential influence on metal mobilities in soil. Thus, we designed an experiment adopting conditions from classical laboratory methods to natural conditions prevailing in metal-rich soils with media spiked with heavy metals, soil agar, and nutrient-enriched or unamended soil incubated with the bacteria. As a result, all strains were able to form struvite minerals (MgNH 4PO 4• 6H 2O) on tryptic soy broth (TSB)-media supplemented with AlCl 3, MnCl 2 and CuSO 4, as well as on soil agar. Some strains additionally formed struvite on nutrient-enriched contaminated and control soil, as well as on metal contaminated soil without addition of media components. In contrast, switzerite (Mn 3(PO 4) 2• 7H 2O) was exclusively formed on minimal media spiked with MnCl 2 by four heavy metal-resistant strains, and on nutrient-enriched control soil by one strain. Hydrated nickel hydrogen phosphate was only crystallized on complex media supplemented with NiSO 4 by most strains. Thus, mineralization is a dominant property of streptomycetes, with different processes likely to occur under laboratory conditions and sub-natural to natural conditions. This new understanding might have implications for our understanding of biological metal resistance mechanisms. We assume that biogeochemical cycles, nutrient storage and metal resistance might be affected by formation and re-solubilization of minerals like struvite in soil at microscale.