Alkalinity regulation of bauxite residue mediated by Penicillium oxalicum: Insights into carbon components dynamics

Microbially-driven alkaline neutralization during soil formation in bauxite residue is a promising technology toward sustainable management of alkaline solid-waste landscapes worldwide. However, our knowledge regarding the impacts of microorganisms on the organic components dynamics involved in alkalinity regulation remains rather limited. In this study, we performed water-phase and solid-phase microcosm experiments using Penicillium oxalicum and sugarcane bagasse with gradient addition amount. Multi-spectroscopic techniques and metabolomic analysis were employed to investigate the combined effects of alkaline stabilization and carbon components dynamics in bauxite residue. An addition of 5 ‰ of sugarcane bagasse was appropriate to reduce the pH of bauxite residue from 10.16 to < 9.0, whilst increasing the content of particulate organic carbon by > 30 %. Spectroscopic analysis verified that sugarcane bagasse predominantly formed connections with humic substances, establishing zones rich in carbon containing fulvic and humic acids, which promoted the bio-production of low-molecular-weight-organic acids. Metabolomic analysis identified 631 compounds, with 126 associated to carbon metabolism. Notably, tricarboxylic acid cycle (TCA) pathway involving acetate and oxalate were significantly up-regulated following the combined application. Mantel-test analysis further showed positive correlations between 5-hydroxyindoleacetic acid and 5-phosphonooxy-L-lysine and alkalinity regulation, proving that the combined application regulated alkalinity by improving amino acid metabolism and carbon skeleton reutilization. Overall, our findings highlighted the metabolic mechanisms involved in alkalinity regulation during soil formation process mediated by P. oxalicum and provided an optimized solution for microbially-driven alkaline regulation within bauxite residue.