Use of Two PGPB Strains for the Valorization of Wastewater Sludge and Formulation of a Biofertilizer for the Recovery of Quercus ilex

In response to the growing demand for agricultural production and the need for more sustainable practices, the use of biofertilizers based on the valorization of agricultural residues is presented as an alternative to traditional chemical fertilizers. This approach seeks to minimize environmental impact and improve soil health in agroforestry systems. The present work studies the effect of two plant growth-promoting bacterial strains (PGPB), <i>Bacillus pretiosus</i> (C1) and <i>Pseudomonas agronomica</i> (C2) on <i>Quercus ilex</i> (holm oak) seedlings. Taxonomic diversity was evaluated by massive sequencing of amplicons of the 16S rRNA gene, as well as the metabolic diversity and antibiotic resistance profile of the bacterial communities. The study also evaluated the impact of PGPB strains on the development of <i>Quercus ilex</i> seedlings. On the other hand, the effect of the biofertilizer on soil bacterial communities was evaluated. The results showed that the addition of biofertilizer significantly improved plant development compared to the addition of traditional irrigation (water) or the addition of fertilizer without the strains. In the same way, it was observed how the addition of the strains reduced the minimum inhibitory concentrations (MIC) in the rhizospheres of the treated individuals compared to traditional irrigation. The metagenomic analysis of the rhizospheric communities revealed the survival of the strains in the soil after their addition in any of the chemical treatments without altering the alpha and beta microbial diversity of the rhizospheric communities.