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Comparative Analysis of Phosphate-Solubilizing Bacteria from Rice Rhizosphere and Earthworm across Rice Field Management Systems as Biofilm-Based Biofertilizer Inoculants
Abstract
Phosphate-solubilizing bacteria (PSB) are crucial microbial resources for improving phosphorus bioavailability and supporting low-input rice production. This study aimed to isolate and characterize high-performing PSB from rice rhizospheres and from the dominant earthworm species, Pontoscolex corethrurus. Samples were collected from 5 paddy field management systems in Central Java, Indonesia, including conventional, semi-organic, and 3 organic systems maintained for 7, 10, and 15 years, respectively. Sampling was conducted purposively at 5 points within each system, with 3 replicates per point. A total of 34 bacterial isolates were obtained using Nutrient agar: 20 from the rice rhizosphere and 14 from the gut of P. corethrurus. All isolates were screened for phosphate-solubilizing ability on Pikovskaya agar and in liquid assays. Morphological, physiological, and functional traits were assessed to evaluate diversity and potential. Rhizosphere isolates showed stronger phosphate-solubilizing activity than earthworm isolates in both assays. All isolates demonstrated biofilm-forming capacity. Four candidate isolates with the best PSB performance were identified: RZ5 and RZ16 (rhizosphere), and CAA and CAE (P. corethrurus). Their solubilization activity values were as follows: ROZ (qualitative = 5.10; quantitative = 6.90 µg ml-1), RZ16 (2.94; 8.89 µg ml-1), CAA (3.34; 5.23 µg ml-1), and CAE (2.79; 6.32 µg ml-1). These findings show ecological differentiation of PSB between rhizosphere and earthworm gut niches and across paddy field management systems. The superior strains identified here present strong potential as biofilm-based biofertilizer inoculants to enhance nutrient cycling and support sustainable rice agroecosystems, although further plant-level validation is still needed.
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