Isolation and screening of potassium solubilizing bacteria from saxicolous habitat and their impact on tomato growth in different soil types

Bacteria that solubilize nutrients in the soil are commonly used as bio-inoculants for promoting the growth of different crop species. However, the influence of potassium (K) solubilizing bacteria (KSB) originating from saxicolous habitat (rock-dwelling) on plant growth has not been frequently examined. In this study, we isolated KSB from saxicolous habitats and estimated their ability to produce plant growth hormone, organic acids, and siderophore that may facilitate plant growth. Fifteen culturable saxicolous bacterial isolates with varied K solubilizing ability were isolated from two sites. Of these, four potential K solubilizers were selected and identified by 16S rRNA gene sequencing. The four bacterial isolates resembled Bacillus subtilis, Bacillus cereus, Bacillus licheniformis, and Burkholderia cenocepacia and produced different organic acids, indole acetic acid, and siderophore under in vitro conditions. Potassium solubilization differed among the bacterial isolates and was significantly influenced by K sources. Inoculation of KSB improved the tomato plant growth parameters like plant height, leaf area, total root length, root/shoot ratio, and tissue K content in sterilized and unsterilized Alfisol, and Vertisol soils under greenhouse conditions. We also observed higher residual K content in the KSB inoculated post-harvest soils. Among the four KSB isolates screened, B. licheniformis and B. cenocepacia presents an excellent prospect as bio-inoculants for improving tomato growth in different soil types. Besides these, the enriched K content in the post-harvest soils may help the growth of subsequent crops in sustainable agriculture.