Enrichment of urban waste compost samples allows the isolation of highly efficient phosphate solubilizing bacteria

Phosphorus is essential for plant growth, development, and responses to biotic and abiotic stress, yet much of the phosphorus in soils occurs in forms that are unavailable to plants, limiting crop productivity. Phosphate-solubilizing bacteria (PSB) represent a promising strategy to enhance phosphorus availability and improve the sustainability of agricultural systems, although many reported isolates exhibit limited solubilization efficiency, highlighting the need for new isolation approaches. This study aimed to isolate and in vitro characterize efficient PSB from composting systems containing urban residues from Quito, Ecuador to identify potential candidate strains for sustainable agriculture. Nine isolates were recovered through an enrichment procedure: six identified as Pantoea spp. and three as Klebsiella spp. All the isolates exhibited high phosphate-solubilizing activity. On solid NBRIP medium, the solubilization index (SI) ranged from 0.74 to 4.14 at day 12, with isolate P3B exhibiting the highest SI. In liquid NBRIP medium, soluble phosphorus reached 515.46 and 700.22 mg/L after 5 days, with P1A showing the highest concentration. Supernatant pH decreased to 4.09-5.06 in all cultures, supporting acidification as a primary solubilization mechanism. This approach enabled the isolation of efficient PSB with potential for biofertilizer development. However, the strong dominance of two genera raises the possibility that the enrichment process may have caused the underrepresentation of other functional taxa. In addition to meeting quality standards for agricultural use, the urban waste compost used in this study highlights the importance of urban waste management strategies for minimizing environmental impacts.