Biological synthesis of nickel nanoparticles using extracellular metabolites of Bacillus sphaericus: Characterization and vector-borne disease control applications

In this study, we use extracellular metabolites of Bacillus sphaericus culture for the biosynthesis of nickel
nanoparticles (BS@NiNPs) and potential larvicidal activity against Anopheles subpictus and Culex quinquefasciatus as well as against Rhipicephalus (Boophilus) annulatus (adult cattle tick). The extracellular metabolites
derived from B. sphaericus culture acts as strong reducing and capping agents, allowing biosynthesis of the
BS@NiNPs. Characterization of the synthesized NiNPs was carried out using various techniques, including
UV�vis spectroscopy, atomic force microscopy (AFM), scanning electron microscopy (SEM), transmission
electron microscopy (TEM), Fourier transform infrared (FTIR) and X-ray diffraction (XRD). The FTIR spectroscopy analysis revealed significant peaks at specific wavenumbers (3435, 2923, 1646, 1406, and 1115 cm�1
),
indicating the presence of functional groups from biomolecules involved in the synthesis of BS@NiNPs. XRD
analysis confirms well-defined peaks observed at 2u = 31.72°, 45.40°, 56.43°, and 75.32°, which correspond
to the lattice planes of 100, 101, 102, and 103 reflections, respectively. SEM and TEM images showed that the
NiNPs exhibited spherical to oval shapes with clustered morphology with an average diameter of the grain
size is about 23 § 2.00. The BS@NiNPs exhibited significant parasitic action against A. subpictus and
C. quinquefasciatus as well as adult cattle tick R. (B) annulatus. It is noteworthy that bacterial pathogens such
as Bacillus species are commonly used for vector bio-control management due to their spore-forming
characteristics. Therefore, the toxicity of BS@NiNPs-treated mosquito larvae and cattle ticks was analyzed for
stress-related enzyme activities, including carboxylesterases, b-glucosidases, and glutathione S-transferases.
In summary, our work shows that BS@NiNPs have the potential to be an efficient larvicide against ticks and
mosquito larvae. The results of this study help to design environmentally benign and long-lasting methods
for biological control, addressing the problems posed by vector-borne diseases