Isolation, biochemical characterization and enzymatic profiling of Plant Growth-Promoting Rhizobacteria associated...

The rhizosphere is a critical hotspot of plant-microbe interactions, where Plant Growth-Promoting Rhizobacteria (PGPR) play key roles in nutrient mobilization, growth promotion and stress tolerance. This study aimed to isolate and characterize PGPR from the rhizosphere of chilli (Capsicum annuum L.). Twenty-three morphologically distinct isolates were obtained and evaluated through morphological, biochemical, enzymatic and molecular approaches. Most isolates exhibited catalase and nitrate reduction activities, while carbohydrate utilization profiles revealed broader metabolic versatility in Lysinibacillus macroides compared to Lysinibacillus fusiformis. Enzymatic screening uncovered a high prevalence of protease, urease, amylase, cellulase and lipase production, key traits linked to nutrient cycling and rhizosphere colonization. Quantitative assessment of protease and lipase activities revealed significant inter-isolate variation, with isolates 4.1 and 2.B exhibiting comparatively higher enzyme indices. Pot tray validation showed that rhizobacterial inoculation enhanced seed germination and early seedling growth, with isolates 4.1 and 2.B performing best. Molecular identification confirmed isolates 4.1 and 2.B as L. fusiformis and L. macroides, respectively, supported by phylogenetic analysis. The dominance of diverse rhizobacterial strains and their hydrolytic enzyme activities reflects their ecological adaptability in semi-arid soils. These findings highlight L. fusiformis and L. macroides as promising biofertilizer candidates for chilli cultivation, offering eco-friendly alternatives to chemical fertilizers and contributing to sustainable, climate-resilient agriculture.