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Green synthesis of nanoparticles has received a lot of attention from scientists globally because it is eco-friendly, relatively rapid, and a cost-effective method. This work presents a method for the green synthesis of nickel oxide nanoparticles (NiO-NPs) using leaf extracts of Populus ciliata as a reducing and stabilising agent. The synthesised NiO-NPs were characterised by ultraviolet-visible spectroscopy, Fourier transform infrared spectroscopy, powder X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. It was found that the synthesised NiO-NPs shapes varied, were highly crystalline, and had a face-centred cubic geometry. The calculated crystallite size of the synthesised nanoparticles was 44 nm. Moreover, the antibacterial activity of the synthesised NiO-NPs was also conducted against Gram-positive bacteria (Bacillus subtilis, Bacillus licheniformis) and Gram-negative bacteria (Escherichia coli and Klebsiella pneumoniae). Bacillus subtillus showed a maximum inhibition zone of 28.1±1.6 mm, whereas Klebsiella pneumonia showed a minimum inhibition zone of 9.2±0.5 mm. It was also found that the antibacterial activity increased with an increase in the concentration of NiO-NPs. Keywords: antibacterial activity, green synthesis, nanoparticles, NiO, Populus ciliata.

Two metal resistant Bacillus cereus strains (AVP12 and NC7401) isolated from metal polluted and nonpolluted rhizospheres of Tagetes minuta were examined for Cr(VI) bioaccumulation potential. It was found that the strains have potential to survive even at metal concentration of 300 mg/l. The per cent removal capacity of Cr(VI) by AVP12 and NC7401 strains was analyzed as a function of environmental factors including pH, incubation time and biosorbate concentration. The optimum pH was found to be 5 andwas selected for further studies. Both Langmuir and Freundlich isotherm models were found suitable for description of Cr(VI) bioaccumulation. The maximum Cr(VI) bioaccumulation capacity by Bacillus cereus AVP12 and Bacillus cereus NC7401 strains isolated from polluted rhizosphere was 181.0 and 107.5 mg/l, respectively while maximum Cr(VI) bioaccumulation capacity by Bacillus cereus AVP12 and Bacillus cereus NC7401 strains isolated from non-polluted rhizosphere was 92.59 and 62.11 mg/l, respectively. Both types of rhizobacterial strains, especially isolated from metal polluted rhizospheres could serve as economical and ecofriendly bioaccumulating agents for removal of Cr(VI).