Contamination of agriculture land by heavy metals is a worldwide risk that has sped up noticeably since the beginning of the industrial revolution. Hence, there arise the demands of heavy metal tolerant plant growth promoting bacterial strains for specific metal contaminated agricultural sites restoration. In this study, 36 bacterial isolates were screened out from the rhizospheric soil of Phaseolus vulgaris. Among these, two bacterial strains AR6 and AR8 were selected based on their higher Cr(VI) tolerance (1200 and 1100 μg/mL, respectively) and the maximum production of plant growth promoting substances. In the molecular characterization study, both the bacterial strains showed 99% homology with Cellulosimicrobium funkei KM032184. In greenhouse experiments, the exposure of Cr(VI) to P.vulgaris inhibited the growth and photosynthetic pigments and increased the enzymatic and non-enzymatic antioxidant expressions. However, rhizosphere bacterial inoculations alleviated the negative effect of Cr(VI) and enhanced the seed germination rate (89.54%), shoot (74.50%),root length (60%), total biomass (52.53%), chlorophyll a (15.91%), chlorophyll b (17.97%), total chlorophyll (16.58%) and carotenoid content (3.59%). Moreover, bacterial inoculations stabilized and modulated the antioxidant system of P. vulgaris by reducing the accumulation of Cr in plant tissues. The present finding shows the Cr(VI) tolerance and plant growth promoting properties of the rhizosphere bacterial strains which might make them eligible as biofertilizer of metal-contaminated soils.

Coleus aromaticus leaf essential oil and its purified constituent, carvacrol, were studied for their inhibition activity of diabetic linked α-amylase and α-glucosidase, and the antiproliferative activity and cytotoxicity on human melanoma cancer (A375) cells; its effect on cell cycle arrest, DNA fragmentation and apoptosis by the cleavage of poly-(ADPribose)-polymerase (PARP) and Bcl-2 gene expression was examined. The essential oil and its constituent carvacrol exhibited inhibitory activities against α-amylase and α-glucosidase. The IC₅₀ values for α-amylase (34.64 ± 1.09; 152.3 ± 1.21 µg mL⁻¹) and α-glucosidase (29.29 ± 1.05; 94.02 ± 0.78 µg mL⁻¹) were obtained for the essential oil and carvacrol respectively. Carvacrol inhibited the growth of A375 cells by inducing apoptosis as evidenced by acridine orange/ethidium bromide staining and flow cytometry analyses. The A375 cells treated with carvacrol for 24 h induced apoptosis by the cleavage of PARP and reduced Bcl-2 gene expression. Carvacrol may induce apoptosis by direct activation of the mitochondrial pathway, which plays a vital role in the anticancer effect.

Soil contaminated by chromium (Cr) is a major concern for sustainable agriculture. Considering this as a basis, the present study was designed to isolate Cr(VI)-reducing and plant growth-promoting bacterial strain from contaminated sampling sources. In this study, Rhizobium strain ND2 was isolated from the root nodules of Phaseolus vulgaris grown in leather industrial effluent contaminated soil. The strain ND2 exhibited strong resistance to different heavy metals and reduced 30 and 50 µg ml⁻¹ concentrations of Cr(VI) completely after 80 and 120 h of incubation, respectively, as well as chromium adsorption and immobilization were confirmed by scanning electron microscopic equipped with energy X-ray spectroscopy. In addition, the strain produced 21.73 and 36.86 µg ml⁻¹ of indole-3-acetic acid at 50 and 100 µg ml⁻¹ of L-tryptophan supplimentations, respectively. Strain ND2 positively affected the exo-polysaccharide, ammonia, protease and catalase production and stimulated root length of various test crops under Cr(VI) stress. Moreover, Rhizobium strain ND2 has the potential to colonize the diverse agricultural crops. Thus, the present findings strongly suggested that the multipotential properties of ND2 could be exploited for bioremediation of contaminated sites with Cr(VI) as well as potential bio fertilizer for enhancing the agricultural productivity.

The aim of this study was to investigate the effect of Cr(VI) on the plant growth-promoting traits of potential rhizobacterial strain isolated from Phaseolus vulgaris rhizosphere. A total of 36 rhizobacterial strains were recovered from the rhizosphere of P. vulgaris. Among these strains, the strain AR8 was specifically selected due to the highest resistance against heavy metals and the maximum production of plant growth-promoting substances. The rhizobacterial strain AR8 was identified as Cellulosimicrobium funkei (KM263188) following 16S rDNA gene sequencing. Strain AR8 solubilized phosphate and produced indole-3-acetic acid (32.57 µg/ml), exopolysaccharide (17.23 µg/ml), ammonia (54.16 µg/ml), catalase, biosurfactant, protease, amylase, and lipase. Under Cr(VI) stress, Cr(VI) concentration-dependent progressive decline in all plant growth-promoting traits of the C. funkei exposed was observed except for exopolysaccharide production, which consistently increased with increasing concentrations of Cr(VI). The root elongation assay resulted that the application of C. funkei strain AR8 significantly increased root length of test crops both in the presence and absence of Cr(VI) compared to uninoculated Cr(VI) treated plants. Moreover, AR8 generated a large number of colonies in diverse agricultural crops. Due to these intrinsic abilities, strain AR8 could be utilized for growth promotion as well as for the remediation of chromium in chromium-contaminated soil.