Multimetal bioremediation and biomining by a combination of new aquatic strains of Mucor hiemalis

Enamul Hoque,Johannes Fritscher

doi:10.1038/s41598-019-46560-7

Enamul Hoque, Johannes Fritscher

Open Access

https://doi.org/10.1038/s41598-019-46560-7

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Abstract

Here we describe a unique microbial biotechnology for simultaneous bioremediation and biomining of twelve ionic metals overcoming the obstacles of multimetal toxicity to microbes. After a thorough search of key microorganisms in microbiomes of many sulfidic springs in Bavaria (Germany) over an area of 200 km2, we found three new strains EH8, EH10 and EH11 of Mucor hiemalis physiologically compatible and capable of multimetal-remediation and enrichment. We combined the multimetal-resistance, hyper-accumulation and elicitation power of EH8, EH10 and EH11 to develop a novel biotechnology for simultaneous removal, fractionation and enrichment of metal ions. As a first step we showed the intracellular fixing and deposition of mercury as nanospheres in EH8’s sporangiospores. Scanning Electron Microscopy-Energy-Dispersive X-Ray analysis revealed binding and precipitation of other applied metal ions as spherical nano-particles (~50–100 nm) at the outer electro-negative cellwall-surface of EH8, EH10 and EH11 sporangiospores. Microbiomes, germinated spores and dead insoluble cellwalls of these strains removed >81–99% of applied Al, Cd, Co, Cr, Cu, Hg, Ni, Pb, U, and Zn simultaneously and furthermore enriched precious Ag, Au and Ti from water all within 48 h, demonstrating the potential of new biotechnologies for safe-guarding our environment from metal pollution and concentrating precious diluted, ionic metals.

Highlights

Increasing global demand and use of various metals/metalloids leads to their accumulation in the environment and thereby simultaneously increases the risk of multimetal-toxicity to various organisms
In contrast to the overall microbial- community role for the metal precipitation[38], it was shown by our previous studies that if a key microorganism for metal removal exists in microbiomes, it can remove toxic metals simultaneously with high efficiency which is comparable to the microbiome itself (Table S1)[5,29]
Hyper-metal accumulating M. hiemalis strains EH8, EH10 and EH11 from sulfidic spring water were tested for metal accumulation after inhibition/toxicity assays

Summary

Introduction

Increasing global demand and use of various metals/metalloids leads to their accumulation in the environment and thereby simultaneously increases the risk of multimetal-toxicity to various organisms. The key obstacle in the development of suitable microbial biotechnology for multimetal bioremediation and biomining is the lack of knowledge about avoiding extreme multimetal toxicity to microorganisms In this context it is worth mentioning that microbial removal of toxic metal mixes of nickel and cadmium from water phase was very difficult because of high multimetal toxicity to Clostridium thermoaceticum even at a concentration of only 1 mM14. Few individual live fungi or dead fungal cell walls have been used for the removal of only a few toxic metals from water[11,33], as the live fungal mix (species/strain) may be mutually antagonistic during growth This could be the reason why the successful use of fungal species/ strain combinations for biotechnological applications was, until now, lacking

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