Revealing the phosphate-solubilizing characteristics andmechanisms of the plant growth-promoting bacterium agrobacterium deltaense C1

Abstract Aims This study explores the phosphate (Pi)-solubilizing characteristics and mechanisms of a novel phosphate-solubilizing bacterium, Agrobacterium deltaense C1 (C1hereafter). Methods and Results The growth-promoting effects of C1 were investigated by gnotobiotic experiments, and the Pi-solubilizing mechanism was revealed by extracellular metabolomics, liquid chromatography analysis, and reverse transcription quantitative polymerase chain reaction (RT‒qPCR). Results showed that C1 significantly increased Arabidopsis biomass and total phosphorus (P) content under P deficiency. Under Ca3(PO4)2 condition, the presence of C1 resulted in a significant and negative correlation between available P content and medium pH changes, implying that Pi dissolution occurs through acid release. Metabolomics revealed C1’s ability to release 99 organic acids, with gluconic acid (GA), citric acid, and α-ketoglutaric acid contributing 64.86%, 9.58%, and 0.94% to Pi solubilization. These acids were significantly induced by P deficiency. Moreover, C1’s Pi solubilization may remain significant even in the presence of available P, as evidenced by substantial pH reduction and high gcd gene expression. Additionally, C1 produced over 10 plant growth-promoting substances. Conclusions C1 dissolves Pi primarily by releasing GA, which enhances plant growth under P deficiency. Notably, its Pi solubilization effect is not significantly limited by available Pi.