Abstract
Due to the importance of phosphorus (P) in agriculture, crop inoculation with phosphate-solubilizing bacteria is a relevant subject of study. Paenibacillus sonchi genomovar Riograndensis SBR5 is a promising candidate for crop inoculation, as it can fix nitrogen and excrete ammonium at a remarkably high rate. However, its trait of phosphate solubilization (PS) has not yet been studied in detail. Here, differential gene expression and functional analyses were performed to characterize PS in this bacterium. SBR5 was cultivated with two distinct P sources: NaH2PO4 as soluble phosphate source (SPi) and hydroxyapatite as insoluble phosphate source (IPi). Total RNA of SBR5 cultivated in those two conditions was isolated and sequenced, and bacterial growth and product formation were monitored. In the IPi medium, the expression of 68 genes was upregulated, whereas 100 genes were downregulated. Among those, genes involved in carbon metabolism, including those coding for subunits of 2-oxoglutarate dehydrogenase, were identified. Quantitation of organic acids showed that the production of tricarboxylic acid cycle-derived organic acids was reduced in IPi condition, whereas acetate and gluconate were overproduced. Increased concentrations of proline, trehalose, and glycine betaine revealed active osmoprotection during growth in IPi. The cultivation with hydroxyapatite also caused the reduction in the motility of SBR5 cells as a response to Pi depletion at the beginning of its growth. SBR5 was able to solubilize hydroxyapatite, which suggests that this organism is a promising phosphate-solubilizing bacterium. Our findings are the initial step in the elucidation of the PS process in P. sonchi SBR5 and will be a valuable groundwork for further studies of this organism as a plant growth-promoting rhizobacterium.
Highlights
Phosphorus (P) is a macronutrient required for plant growth
We aimed to relate some genes of P. sonchi SBR5, which were differentially expressed with two distinct P sources (SPi and in Soluble (SPi) and Insoluble (IPi)) to the physiological analysis of phosphate solubilization (PS) processes
Our findings revealed that IPi condition changed carbon metabolism and vitamin biosynthesis of SBR5 and expressed flagellation genes and activated osmoprotection
Summary
Phosphorus (P) is a macronutrient required for plant growth. Plant roots can absorb P in the form of orthophosphates, either H2PO4− or HPO42−, but the concentration of these ions in the soil is in the micromolar range (Shin et al, 2004; Ai et al, 2009). Mineral P can be, for example, found associated with the surface of iron or aluminum oxides in the soil, making it poorly soluble and unavailable for plant nutrition (Shen et al, 2011). Those factors lead to the overuse of chemical P fertilizers and animal manure applied to agricultural land, which— soil fertility and crop production are improved—caused severe environmental damage in the past decades, such as eutrophication of rivers and lakes, and the input of cadmium and radionuclides in the soil from contaminated fertilizers (Vance et al, 2003; Attallah et al, 2019; Li et al, 2020; Lee et al, 2020). Besides providing soluble P to plants, these organisms promote plant growth and development by other activities, such as nitrogen fixation and production of plant phytohormones (Zaidi et al, 2009)
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