Interaction Between Different Amoebae and Pseudomonas sp. Impacts Rice Plant Growth and Phosphorus Dynamics

Microorganisms play a key role in mineralizing phosphorus (P) in the soil, thereby reduces the P deficiency in plants. However, it is largely unknown how the interactions between phosphate-solubilizing bacteria and bacterivorous protists influence P dynamics. Therefore, the present study was conducted to investigate the interactive impact of phosphate-solubilizing Pseudomonas sp. (Ps) and three amoebae species (Vermamoeba vermiformis (A9), Acanthamoeba lenticulata (A10), and Acanthamoeba genotype T4 (A23)) on P dynamics in soil and plants. A significant enhancement in plant growth parameters was observed in amoebae-Ps combined treatments compared to the control and Ps alone treatments. The combined A10Ps (A. lenticulata + Pseudomonas sp.) and A23Ps (Acanthamoeba genotype T4 + Pseudomonas sp.) had a greater effect on plant P uptake (4.40 mg g^-1, and 4.60 mg g^-1, respectively) compared to the Ps alone treatment (3.84 mg g^-1). The alkaline phosphatase activity (APA) was significantly greater in A23Ps (417.68 µg pNP g^-1 24 h^-1). Similarly, the percentage of siderophore units (PSU), which is a quantitative expression used to measure the relative amount of siderophore produced by bacteria was higher (95.30%) in A10Ps treated soil. This was ultimately reflected by a higher percentage increase in soil available phosphorus (AP) in A23Ps (57.81%) and A10Ps (53.34%) than in the control treatment. These findings show that the trophic interactions between Pseudomonas sp. and amoebae play an important role in solubilizing P in a natural soil environment, therefore, it is advantageous to develop Pseudomonas sp. amoebae combined bioinoculants to enhance nutrient mineralization, availability, and ultimately growth of plant. However, before practical recommendations for field trials are made, a wide range of such interactions should be evaluated with broader taxonomic and functional screening along with molecular analysis.