Metabolic insight into the role of microbial interplay in conferring drought stress tolerance in black cumin (Nigella sativa L.).

Abstract

Main conclusion: Serendipita indica and Pseudomonas fluorescens improved drought resilience in Nigella sativa by enhancing stress-related physiological and metabolic responses, including nutrient uptake, antioxidant activity, osmolyte accumulation, and photosynthetic efficiency. Utilizing metabolomic analysis combined with physiological studies, we evaluated the microbial interplay between Serendipita indica and Pseudomonas fluorescens in metabolite adjustments of black cumin (Nigella sativa L.) under drought stress conditions (D0: well-watered, D1: moderate drought at 60% field capacity, D2: severe drought at 40% field capacity). Metabolomic profiling and physiological measurements were conducted to assess plant growth, photosynthetic capacity, ionomic status, accumulation of compatible osmolytes (amino acids, organic acids, sugars), and activities of antioxidant enzymes (ascorbate peroxidase, catalase, and glutathione peroxidase). A synergistic effect between S. indica and P. fluorescens was observed under D1, while S. indica alone conferred more pronounced benefits under D2. Inoculated plants particularly those treated with S. indica, exhibited elevated levels of essential nutrients (N, Fe, Ca), osmolytes (glucose, fructose), and drought-responsive amino acids. Peak levels of aspartic acid (Asp), glutamine (Gln), glycine (Gly), gamma-aminobutyric acid (GABA), histidine (His), valine (Val), arginine (Arg), and leucine (Leu) were detected under severe drought in response to microbial treatments. This study provides the first integrative metabolomic and physiological evidence of microbe-mediated drought tolerance in Nigella sativa, highlighting the synergistic potential of fungal-bacterial consortia as a sustainable strategy to enhance crop resilience under water-limited conditions.