Soil regeneration using wastewater treatment plant sludge and plant growth-promoting bacteria in Quercus ilex: implications for antibiotic resistance within a One Health framework

Abstract

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 analyzes, nutritional and antibiotic resistance evaluations were carried out, all providing significant results. Treatments with WWTP sludge, 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, PGPB-inoculated treatments did not show a generalized increase in phenotypic antibiotic resistance under the experimental conditions tested, which is fundamental within the context of the " One Health " approach pursued throughout this work.