Distinct Mineral Weathering Behaviors of the Novel Mineral-Weathering Strains Rhizobium yantingense H66 and Rhizobium etli CFN42.

Bacteria play important roles in mineral weathering, soil formation, and element cycling. However, little is known about the interaction between silicate minerals and rhizobia. In this study, Rhizobium yantingense H66 (a novel mineral-weathering rhizobium) and Rhizobium etli CFN42 were compared with respect to potash feldspar weathering, mineral surface adsorption, and metabolic activity during the mineral weathering process. Strain H66 showed significantly higher Si, Al, and K mobilization from the mineral and higher ratios of cell numbers on the mineral surface to total cell numbers than strain CFN42. Although the two strains produced gluconic acid, strain H66 also produced acetic, malic, and succinic acids during mineral weathering in low- and high-glucose media. Notably, higher Si, Al, and K releases, higher ratios of cell numbers on the mineral surface to total cell numbers, and a higher production of organic acids by strain H66 were observed in the low-glucose medium than in the high-glucose medium. Scanning electron microscope analyses of the mineral surfaces and redundancy analysis showed stronger positive correlations between the mineral surface cell adsorption and mineral weathering, indicated by the dissolved Al and K concentrations. The results showed that the two rhizobia behaved differently with respect to mineral weathering. The results suggested that Rhizobium yantingense H66 promoted potash feldspar weathering through increased adsorption of cells to the mineral surface and through differences in glucose metabolism at low and high nutrient concentrations, especially at low nutrient concentrations. IMPORTANCE This study reported the potash feldspar weathering, the cell adsorption capacity of the mineral surfaces, and the metabolic differences between the novel mineral-weathering Rhizobium yantingense H66 and Rhizobium etli CFN42 under different nutritional conditions. The results showed that Rhizobium yantingense H66 had a greater ability to weather the mineral in low-and high-glucose media, especially in the low-glucose medium. Furthermore, Rhizobium yantingense H66 promoted mineral weathering through the increased adsorption of cells to the mineral surface and through increased organic acid production. Our results allow us to better comprehend the roles of different rhizobia in silicate mineral weathering, element cycling, and soil formation in various soil environments, providing more insight into the geomicrobial contributions of rhizobia to these processes.