Culturable endophytic Pseudomonas fluorescens Z1B4 isolated from Zanthoxylum alatum Roxb. with stress-tolerance and plant growth-promoting potential

Endophytes are an important constituent of sustainable agriculture because of their ability to produce a large number of agriculturally important metabolites. A salt-tolerant fluorescent green pigment-producing endophytic bacterium was isolated on 2.5% NaCl-supplemented nutrient agar from the leaf samples of Zanthoxylum alatum Roxb. The isolate Z1B4 was identified as Pseudomonas fluorescens based on morphological features, fatty acid methyl ester analysis, biochemical tests, and 16S rRNA gene sequencing. P. fluorescens Z1B4 showed positive results for tricalcium phosphate solubilization; 1-aminocyclopropane-1-carboxylate (ACC) deaminase activity; and production of auxins, siderophores, hydrogen cyanide, and ammonia. P. fluorescens Z1B4 also showed strong antagonistic activity against Curvularia lunata (MTCC 283), Fusarium verticillioides (MTCC 3322), and Alternaria alternata (MTCC 1362) and exhibited stress tolerance to a wide range of temperature and pH and concentrations of NaCl and calcium salts. Under natural conditions, following inoculation with the isolate Z1B4, a significant increase in the growth of pea and maize test plants in pots was observed compared to that of uninoculated control plants. The rifampicin-resistant mutant Z1B4^Rif was recovered from the roots, shoots, and leaves of the test plants, indicating that the isolated endophytic bacterium can grow well within different plant tissues. The present study indicated that the endophytic bacterium P. fluorescens Z1B4 can be used as a bacterial inoculant in stressed environments for sustainable agriculture.