Abstract

Purpose: Bacillus (such as Bacillus velezensis) are marketed as plant growth–promoting bacteria (PGPB). The ?–propeller phytase (BPP)–carrying Bacillus can release inorganic phosphate from phytate hydrolysis and thereby improve the plant growth in P deficient soils. However, our knowledge on BPP–carrying Bacillus during germination and the early stages of plants is still limited. Here, we quantified the abundance of Bacillus BPP genes in seeds of tomato inoculated with a seed–endophytic Bacillus and germinated on agar with and without P. Methods: The specificity of chosen primer set was first confirmed for the detection of the Bacillus BPP gene in seed–endophytic Bacillus velezensis–like strains (Bacillus sp. S–30, S–23 and P–28) by digital PCR (dPCR). Tomato seeds were inoculated with Bacillus sp. S–30, germinated and grown on agar supplemented with insoluble phosphate and phytate. Seedlings were harvested at 11 and 21 days and the presence of Bacillus BPP gene in gDNA extracts and cDNA was determined by dPCR. Results: Both at days 11 and 21 post–germination, the inoculation of strain Bacillus sp. S–30 resulted in greater biomass of the inoculated seedlings. In general, dPCR revealed a significant (p < 0.05) greater abundance of the BPP gene in DNA extracts and cDNA from inoculated seedlings with Bacillus sp. S–30 in both sampling days. Overall, a higher expression of BPP was observed in inoculated seedlings, particularly in phytate–supplemented agar. Conclusion: Bacillus BPP gene was successfully used to quantify by dPCR inoculated Bacillus sp. S–30 and BPP–carrying Bacillus in tomato seedlings post–germination. © The Author(s) under exclusive licence to Sociedad Chilena de la Ciencia del Suelo 2025.