Characterization of lead resistant endophytic Bacillus sp. MN3-4 and its potential for promoting lead accumulation in metal hyperaccumulator Alnus firma.

The aim of this study was to isolate and characterize endophytic bacteria from the roots of the metal hyperaccumulator plant Alnus firma. A total of 14 bacterial endophytes were isolated from root samples and assayed for tolerance to heavy metals. Isolate MN3-4 exhibited maximum bioremoval of Pb and was subsequently identified as Bacillus sp. based on 16S rRNA sequences. The pH and initial metal concentration highly influenced the Pb bioremoval rate. The growth of isolate MN3-4 was moderately altered in the presence of metals. Scanning electron microscopy, energy dispersive spectroscopy, biological-transmission electron microscopy, and Fourier transform infrared spectroscopy studies revealed that isolate MN3-4 had extracellularly sequestered the Pb molecules with little intracellular accumulation. Isolate MN3-4 did not harbor pbrA and pbrT genes. Moreover, isolate MN3-4 had the capacity to produce siderophores and indoleacetic acid. A root elongation assay demonstrated an increase (46.25%) in the root elongation of inoculated Brassica napus seedlings compared to that of the control plants. Obtained results pointed out that isolate MN3-4 could potentially reduce heavy metal phytotoxicity and increase Pb accumulation in A. firma plants.