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Solubilization of Magnesium-Bearing Silicate Minerals and the Subsequent Formation of Glushinskite by Aspergillus niger

Microbes may play a substantial role in the weathering and alteration of minerals. However, not enough concerns have been realized about the complexity of microbe-mineral interactions. The present work reports the interactions between fungi and minerals with emphasis on the role of silicate minerals as the metal donor for the precipitation of secondary mineral. Herein, two magnesium-bearing silicate minerals with different structures, forsterite and talc, were added to the submerged cultures of Aspergillus niger (A. niger). It is shown that forsterite exhibits a better solubilization effect than talc, and the secondary mineral glushinskite only precipitates in the presence of forsterite substrates. Oxalic acid excreted by A. niger plays a key role in the biological leaching and mineralization processes. Moreover, the forsterite particles with certain size added to the cultures tend to inhibit the aggregation of fungal biomass, and therefore affect the morphology of A. niger aggregates in the submerged culture. With varying forsterite particle size, distinct fungal morphological forms including mycelial pellets and freely dispersed hyphae can be formed, which have a direct impact on fungal metabolism and ultimately result in varied crystallization habits of the neo-minerals. Particularly in the culture with −40/+60 mesh forsterite particles, the mineralized glushinskite mainly exhibit tubular forms; whereas when forsterite particles were at −100/+120 mesh or −200 mesh, pyramidal prisms are obtained. We show that the environmental factors such as the particle size of mineral substrate could influence the fungal morphology and metabolic activities, thereby leading to different morphological neo-minerals. The dependence of biomineral morphology on the environmental factors can open up a novel avenue to understanding the microorganism-environment interactions.