Microbial Strategy Shift for Releasing Iron with Varying Mineral Substrates and their Accessibility: Implications for Iron Biomining

Since the dawn of human civilization, discovery of metals, especially iron (Fe), has played a pivotal role in the growth and diversification of human societies and industries. Steel, a metallurgical engineering marvel, is considered the backbone of any economy. Despite the immense importance and demand, Fe supply chains are highly compromised. The dominance of low-grade ores and highly positive carbon footprint of Fe ore processing presses demand green technologies like biomining. Understanding the intricate mechanisms by which microbes encourage mineral dissolution is pivotal in bioleaching. This study addresses a critical knowledge gap by examining the ability of Pseudomonas aeruginosa to mobilize Fe from mineral (ferrihydrite, goethite, and hematite) and rock surfaces (basalt glass and crystalline basalt), selected to mimic the mineralogy of critical and oxide Fe ores, such as laterites. Fe acquisition poses challenges to P. aeruginosa due to its limited availability in diverse environments. To overcome this limitation, bacteria employ sophisticated strategies, including synthesizing and secreting siderophores, small molecules with a high affinity for Fe, to scavenge and uptake Fe effectively. In this study, we investigated the role of siderophores in facilitating Fe uptake from various Fe sources by P. aeruginosa. Experimental setups involved incubating Fe oxides and basalt separately in sterilized Teflon flasks containing an Fe-limiting growth medium, each inoculated with a P. aeruginosa strain. Results demonstrated a significant increase in extracted Fe when siderophores were present, indicating a siderophore-driven process in Fe mobilization. Our findings highlight the complex regulatory network governing Fe mobilization in P. aeruginosa, emphasizing the interplay between quorum sensing (QS) and the Fe sequestration system. Unraveling these molecular mechanisms advances our understanding of microbial Fe acquisition strategies and opens avenues for understanding the innovative survival strategies employed by bacteria in Fe-limiting environments. Such studies are important for scaling up ferredox (a biohydrometallurgical concept for oxide ores) biomining processes for industrial use.