Taking nature into lab: biomineralization by heavy metal-resistant streptomycetes in soil

Abstract

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 nutrientenriched or unamended soil incubated with the bacteria. As a result, all strains were able to form struvite minerals (MgNH4PO4 6H2O) on tryptic soy broth (TSB)-media supplemented with AlCl3, MnCl2 and CuSO4, 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 (Mn3(PO4)2 7H2O) was exclusively formed on minimal media spiked with MnCl2 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 NiSO4 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

Siderophore production by streptomycetes—stability and alteration of ferrihydroxamates in heavy metal-contaminated soil

“…Thirty grams of soil was transferred into sterile tubes (Greiner Bio One, 100 ml with screw top), inoculated with 0.648 g of fresh bacterial biomass (for fermentation protocol and further details, see Schütze et al 2013Schütze et al , 2014 of either the extremely heavy metal-resistant Streptomyces mirabilis P16B-1 (Schmidt et al 2008) or the metal-sensitive control strain Streptomyces lividans TK24 (Amoroso et al 2002;Ravel et al 2000). Soil was set to a water holding capacity of 70 % by addition of sterile tap water.…”

“…The recovery of siderophores from metal-containing soil was tested with the water-soluble fraction (pH of soil slurry was adjusted at pH 8 by use of hydroxide to allow for stable siderophore complexes; K f at neutral pH: FOE 10 32.5 , FOB 10 30.5 ; Hider and Kong 2010; Dhungana et al 2004), shaking at room temperature for 30 min (3015, GFL shaker), incubation at 4°C for 60 min, centrifugation at 14,000 rpm for 10 min, and filtration <45 μm of 50 g of fresh soil samples (see Schütze et al 2013) after supplementation with SCF (iron-free solution; 81.6 μM siderophore content). The SCF itself was used as a control to calculate the initial siderophore concentration.…”

Potential of Bioremediation and PGP Traits in Streptomyces as Strategies for Bio-Reclamation of Salt-Affected Soils for Agriculture

“…Microorganisms are also able to prevent the entry of toxic substances by adhering them to the cell membrane [82], and developing cytoplasmic protection mechanisms through inclusion bodies that retain a large number of toxic substances [81] to immobilize them. Besides, some microorganisms can immobilize toxic elements by forming biominerals with them inside or outside their cells [6,83,84].…”

“…Biomineralization can happen through two different mechanisms: biologically controlled mineralization (BCM) and biologically induced mineralization (BIM) [84]. There is evidence of biominerals produced by Streptomyces by active and passive mechanisms in BIM [6,22,83], where the formation occurs as a consequence of changes in the oversaturation of the system [85]. Active mechanisms comprise the capture or excretion of different metabolites [86].…”

Bio-precipitates produced by two autochthonous boron tolerant Streptomyces strains

“…On the whole, biominerals count with calcium as major cation, iron being the second most common, while phosphates, oxides, and carbonates happen to be the most numerous anions [4]. There is evidence of numerous bacterial genera which produce biominerals, such as Pseudomonas [10] Bacillus [11] and Vibrio [12] that mediate the precipitation of calcite under well-defined conditions, sulphate reducing bacteria and cyanobacteria involved in dolomite formation [13], Myxobacteria that allows obtaining struvite and calcite crystals in presence of the cellular membrane fraction [14], Halobacillus which precipitates carbonates at different salt and magnesium/calcium ratios concentrations [15], Shewanella capable of inducing extracellular precipitation of magnetite [16] and Streptomyces associated with hydromagnesite and needle-fiber aragonite deposits [17] and struvite biominerals in which Mg is replaced by Ni [18, 19]. Biominerals are increasingly being exploited in bio-nanotechnology, focused on exploiting ferritins [20], magnetite nanoparticles as Magnetic Resonance Imaging (MRI) contrast agents, ferrofluids, magnetic recording materials, therapeutic delivery vehicles [21], and on the remediation of other contaminants such as chromium [22], nickel [18] and cobalt [23].…”