Biomineralization capabilities of streptomyces mirabilis P16B 1 : insights into struvite and nickel struvite synthesis and their implications Microorganisms thriving in extreme environments have evolved remarkable strategies to cope with harsh conditions often presenting significant biotechnological potential. Former mining sites known for their high concentrations of heavy metals and low pH provide an extreme environment for microbial adaptation. Streptomyces mirabilis P16B 1 was previously isolated from a former uranium mine near Ronneburg Germany. This strain presents high tolerance to nickel and other heavy metals along with the ability to produce biominerals. The objective of this research was to elucidate the underlying mechanism behind this process. The mineral produced by S. mirabilis P16B 1 was identified as struvite. In the presence of nickel this metal is incorporated into the mineral structure forming Ni struvite. The biomineralization of struvite occurs with limited control by the bacterium over the process. Mineral precipitation was induced due to the increasing concentration of ammonium in the vicinity of the cell as a result of metabolic activity and consequent rise in the pH thus increasing the supersaturation of the mineral. Moreover the activity of the nickel exporter NreB in the presence of nickel results in an increased concentration of this metal near the cell thereby increasing the supersaturation of Ni struvite. Analyses of the metabolome and secretome of the strain revealed the involvement of organic molecules in the mineralization process. The precipitation of struvite provides advantages to the bacterium such as immobilization of nutrients like nitrogen and phosphate which can later be solubilized by the bacterium. Additionally the precipitation of Ni struvite adds to the extreme tolerance of this bacterium by immobilizing the metal extracellularly which also benefits other microorganisms in the environment. This ability to immobilize nickel coupled with its involvement in nutrient cycling positions S. mirabilis P16B 1 as an important member of the soil community.