Recovery of a WWTP fertilizer added with plant growth promoting bacteria (PGPB). Relationship with antibiotic resistance in the "One Health" environment with an oak species: Quercus ilex

Soil degradation is a critical problem in Spain, aggravated by intensive agricultural practices, urbanisation and natural phenomena such as forest fires. This study addresses soil regeneration through the valorisation of waste from wastewater treatment plants (WWTP) and its supplementation with plant growth-promoting bacteria (PGPB). Quercus ilex , a species of holm oak of significant importance in Spain, was used as a model to evaluate the effects of these treatments on plant growth and soil health. In this research, plant growth assays, metabolic and taxonomic diversity analyses, nutritional and antibiotic resistance evaluations were carried out, all providing significant results. Treatments with EDAR waste, both sterilized and non-sterilized, significantly improved the growth of Quercus ilex , showing highly positive effects after PGPB supplementation, evaluating in this study Bacillus pretiosus (C1) and Pseudomonas agronomica (C2) strains, showing improvements in nutrient uptake and stress tolerance. Moreover, understanding what is happening requires considering microbial diversity, which plays a crucial role in understanding soil functions and transformations. The microbial diversity analysis revealed high diversity in all treatments, with changes observed in the composition of the soil microbial community. Additionally, treatments with PGPB did not increase antibiotic resistance in soil microbial communities, which is fundamental within the context of the " One Health " approach pursued throughout this work.