Changes in the Weathering Activity and Populations of Culturable Rock-Weathering Bacteria from the Altered Purple Siltstone and the Adjacent Soil

A total of 150 bacteria were isolated from the less and more altered (weathered) purple siltstones and the adjacent soils to compare the changes in the rock weathering patterns and populations of rock-weathering bacteria. The proportions of the highly effective Fe and Si solubilizers were significantly different among the altered rocks and soils. Maximum proportions of the highly effective Fe, Si, and Al solubilizers were observed in the soils, while significantly higher proportion of the highly effective K solubilizers was observed in the more altered rocks and the soils. The rock-weathering bacteria belonged to 37 bacterial species, among which 36, 64, and 56% of the species were specific to the less and more altered rocks and the soils, respectively. In the rock-weathering process, strains M78 and L38 mainly produced acetic acid, while strain H28 mainly produced gluconic acid. Furthermore, dominant rock-weathering members of Ensifer genus had the higher ability to release Fe and Si, while dominant rock-weathering members of Bacillus had the higher ability to release K. The results suggest the changes in the element mobilization patterns and populations of the rock-weathering bacteria and highlight the possible role of these bacteria in the rock weathering and soil formation.