Clostridium pasteurianum in kaolin bioleaching: Iron reduction and whitening mechanisms

Abstract

Previous studies have shown that microbial consortia outperform single strains in bioleaching processes. However, gaps remain in understanding the microbial community structure and functional interactions between key species and critical metabolic genes. This study addressed these questions through iron-reducing microbe-mediated bioleaching experiments combined with multi-omic approaches. The study found four major findings: (1) Bioleaching significantly enhanced the whiteness of kaolin from 60.8 to 90.4 % by selectively removing Fe (III), reducing the Fe (III) content from 1.5 % to 1.2 % without altering the kaolin structure. This process was accompanied by the solubilization of Fe (II). (2) Community succession identified Clostridium (87.7 %), Lysinibacillus (5.9 %), and Bacillus (0.7 %) as the dominant populations. Spearman analysis confirmed strong positive correlations between Clostridium abundance, Fe²⁺ concentration, and whiteness (p < 0.05), suggesting that together with Fe (III) content in kaolin Clostridium plays a key role in whitening. (3) Metagenomic reconstruction revealed Clostridium pasteurianum (50.8 %) was the core functional species. Its complete glycolysis/pyruvate metabolism pathways and acidogenesis gene clusters (lactic/formic/butyric acids) synergistically facilitated Fe (III) dissolution. Notably, this strain exhibited enriched ferredoxin-coding genes and membrane-bound electron transport chain components, suggesting it had a pivotal role in dissimilatory iron reduction. This work provides the first elucidation of structure-function relationships and metabolic networks within iron-reducing consortia, offering both theoretical foundations and practical strategies for sustainable mineral bio-processing.