16S rRNA gene-based identification and plant growth-promoting potential of cultivable endophytic bacteria

Endophytic bacteria play essential roles in plant growth and fitness through nitrogen fixation, nutrient solubilization, and phytohormone production. However, the plant growth-promoting (PGP) potential of endophytic microorganisms inhabiting vegetables is underexplored. Thus, this study investigated the endophytic bacteria of vegetable crops for their PGP properties using the culture-dependent technique. Recovered isolates were identified by sequencing the partial 16S rRNA gene using Sanger sequencing. The isolated endophytic bacteria belonged to 15 genera and 39 different species. Bacillus, Enterobacter, Pantoea, and Pseudomonas were the predominant genera and had high phosphate solubilization and siderophore production potential. The isolates differentially produced indole-3-acetic acid and ammonium in the range 0.14-44.48 mu g mL(-1) and 0.77-93.24 mg L-1, respectively. Pseudomonas azotoformans, Stenotrophomonas maltophilia, and Serratia liquefaciens showed a high level of siderophore production, which was not significantly (p > 0.05) different across the plant and organ types. More than 21% of endophytes could produce gelatinase, protease, amylase, and cellulase, contributing to their diverse ecosystem functions. Bacterial density and species composition varied across the vegetable species, organs, and farm locations but were higher in the stems compared with other organs. However, the vegetable organ had no significant (p > 0.05) influence on the bacterial population density, except for the interaction of plant species and organs. Overall, this study provides basic knowledge about the cultivable endophytic bacterial community of vegetables and reveals diverse endophytic bacteria useful in bioinoculant formulations for improving crop productivity.