Isolation and Characterization of Phosphate-Solubilizing Bacteria from Compost and Open Dump Sites: Implications for Plant Growth

Phosphorus (P) is a vital macronutrient for plant growth. The bioavailability of P in soils is limited due to the insolubility of P. This study aimed to isolate and characterize Phosphate Solubilizing Bacteria (PSB) strains and determine their efficiency of phosphate solubilization and their effect on plant growth. pH, Electrical Conductivity (EC), Total Organic Carbon (TOC), organic nitrogen, and available phosphorus in soil were analyzed. Pikovskaya’s Agar (PKV) was used to isolate PSB strains and identified through biochemical tests and 16S rRNA gene sequencing. The solubilization efficiency of the isolates was assessed in PVK broth supplemented with 0.5% tricalcium phosphate (TCP), and their effect on plant growth was evaluated in pot experiments. Mung bean (Vigna radiata) was selected as the experimental plant. Five Bacillus strains were identified, and the genotypic test was confirmed as Bacillus pumilus strain PRE14, Bacillus altitudinis 41KF2b, Bacillus cereus ATCC 14579, Bacillus siamensis strain KCTC 13613, and Bacillus subtilis strain NCIB 3610. All isolated strains were positive for the catalase test, gram staining, motility test, starch hydrolysis test, and spore staining test. The citrate utilization test and the spot test for indole production were negative for isolated PSB strains. B. siamensis strain KCTC 13613 showed the highest phosphate solubilizing efficiency with the maximum phosphorus concentration of 9.17±0.07 mg/kg recorded after 6 days of incubation. Pot experiments revealed that potting media inoculated with B. siamensis strain KCTC 13613 exhibited the highest shoot length (mean increase of 16.77 ± 0.74 cm), root length (mean increase of 10.99 ± 0.41 cm), and wet weight (mean increase of 0.60 ± 0.08 g) compared to other isolated PSB strains. All isolated Bacillus spp. Strains demonstrated a significant difference (n=9, P < 0.05) in measured growth parameters compared to plants grown under the control potting media. Soil pH increased post-germination, with the lowest pH recorded at 7.40±0.09 for media inoculated with B. siamensis strain KCTC 13613, indicating organic acid production. These findings reveal the potential of Bacillus spp. as bio-inoculants to promote sustainable agriculture by enhancing phosphorus availability and plant growth.