Biorefining of Anaerobic Digestates for the Recovery of Biostimulants and Bioelicitors for Immune Priming and Plant Protection

Olive oil production is a major global agricultural industry that generates significant waste, particularly olive pomace, which poses environmental and economic challenges. Anaerobic digestion emerges as a promising solution for its valorization into biogas. However, the resulting digestate remains underutilized and its long-term environmental impact is uncertain. Traditional disposal methods are costly and inefficient, underscoring the need for more sustainable approaches. In this study, olive pomace digestate was biorefined, and its components were upcycled into soil amendments and plant immunostimulants. Metagenomic analysis revealed a diverse microbial community in the liquid fraction. A microbial-enriched protein extract (MIPE) was obtained, containing precursors of microbe- and damage-associated molecular patterns, including Flagellin, Elongation Factor Tu, and the plant phytocytokine Golven. Plant treatment with MIPE triggered a rapid immune response, characterized by oxidative burst, mitogen-activated protein kinase activation, and the upregulation of defense-related genes such as CYP81F2, FRK1, and WRKY53. MIPE-induced priming enhanced Arabidopsis and tomato resistance to Botrytis cinerea and Pseudomonas syringae. Our findings highlight olive pomace digestate as a valuable growth biostimulant, with its liquid fraction also representing a promising resource of immunity bioelicitors. This refinement valorizes olive mill waste, providing a sustainable alternative to chemical fertilizers and pesticides and supporting sustainable agriculture.