Inoculation with endophytic Bacillus megaterium alleviates lead toxicity in cherry tomato

Abstract The current research was designed to assess Pb tolerance and growth-enhancing capabilities of an endophytic bacterium obtained from mangrove foliage in Saudi Arabia, and to determine its effectiveness in mitigating Pb-induced stress in tomato plants. An endophytic bacterial strain was isolated from mangrove leaves collected from the Saihat Mangrove, Saudi Arabia. Pb tolerance was assessed through growth assays under increasing concentrations of Pb (NO 3 ) 2 to determine the maximum tolerable concentration (MTC). Molecular characterization was carried out through sequencing of the 16S rRNA gene region. The obtained isolate was confirmed as Bacillus megaterium , displaying greater than 98% sequence similarity (accession: PV018404). The bacterium exhibited uninhibited growth at 50 ppm Pb(NO 3 ) 2 , partial growth suppression at concentrations ranging from 100–250 ppm, and pronounced inhibition between 350–450 ppm. The maximum tolerable concentration was determined to be 450 ppm, at which bacterial growth remained markedly reduced compared to untreated samples (p < 0.05).The strain exhibited multiple plant growth–promoting traits. In uncontaminated soil, inoculated tomato plants showed increases of 6–24% in shoot and root length and dry biomass compared with controls. Under Pb-contaminated soil (720 ppm Pb), inoculation significantly alleviated Pb stress, enhancing shoot length by 23%, root length by 26%, and shoot and root dry weight by 37%.Nutrient uptake was also improved, with increases in N, P, and K of 4.5%, 25.3%, and 13.8% in uncontaminated soil, and 37.9%, 3.6%, and 26.7% under Pb stress, respectively. These results demonstrate that B. megaterium tolerates high Pb levels while enhancing plant growth and nutrient acquisition, highlighting its promise as a bioinoculant for Pb-contaminated soils.