Abstract
Halophiles are the organisms that thrive in extreme high salt environments. Despite the extensive studies on their biotechnological potentials, the ability of halophilic prokaryotes for the synthesis of nanoparticles has remained understudied. In this study, the archaeal and bacterial halophiles from a solar saltern were investigated for the intracellular/extracellular synthesis of silver and selenium nanoparticles. Silver nanoparticles were produced by the archaeal Haloferax sp. (AgNP-A, intracellular) and the bacterial Halomonas sp. (AgNP-B, extracellular), while the intracellular selenium nanoparticles were produced by the archaeal Halogeometricum sp. (SeNP-A) and the bacterial Bacillus sp. (SeNP-B). The nanoparticles were characterized by various techniques including UV-Vis spectroscopy, XRD, DLS, ICP-OES, Zeta potentials, FTIR, EDX, SEM, and TEM. The average particle size of AgNP-A and AgNP-B was 26.34 nm and 22 nm based on TEM analysis. Also, the characteristic Bragg peaks of face-centered cubic with crystallite domain sizes of 13.01 nm and 6.13 nm were observed in XRD analysis, respectively. Crystallographic characterization of SeNP-A and SeNP-B strains showed a hexagonal crystallite structure with domain sizes of 30.63 nm and 29.48 nm and average sizes of 111.6 nm and 141.6 nm according to TEM analysis, respectively. The polydispersity index of AgNP-A, AgNP-B, SeNP-A, and SeNP-B was determined as 0.26, 0.28, 0.27, and 0.36 and revealed high uniformity of the nanoparticles. All of the synthesized nanoparticles were stable and their zeta potentials were calculated as (mV): ˗33.12, ˗35.9, ˗31.2, and ˗29.34 for AgNP-A, AgNP-B, SeNP-A, and SeNP-B, respectively. The nanoparticles showed the antibacterial activity against various bacterial pathogens. The results of this study suggested that the (extremely) halophilic prokaryotes have great potentials for the green synthesis of nanoparticles.
Highlights
Halophilic prokaryotes are salt-loving microorganisms that cannot survive in the absence of salts
All the extreme halophiles were identified as Archaea and all the moderates were identified as Bacteria based on their susceptibility and resistance to the anisomycin, respectively
We used extreme and moderate halophiles isolated from a solar saltern for the green synthesis of silver and selenium nanoparticles
Summary
Halophilic prokaryotes are salt-loving microorganisms that cannot survive in the absence of salts (most special NaCl). Moderate halophiles grow optimally under 1.5 M salt concentrations, and most of them belong to the Bacteria They use some organic compounds called compatible solutes (compatible with cellular macromolecules) to counter the high osmosis pressure. Extreme halophiles grow optimally in the presence of more than 1.5 M salts (up to 5 M), and most of them belong to the Archaea They store a high amount of salts (especially KCl) inside their cells to balance the osmosis pressure [1]. The salinity increases gradually through the effects of the wind and temperature with the salt produced at the last pond being called the crystallizer pond [2] Living in these extreme environments (high salt concentration, high UV radiation, low water content) requires unique cell components, different form nonhalophile (micro)organisms. Halophile macromolecules have the potential to be used in biotechnological processes such as biopolymers, hydrolytic enzymes, biosurfactants, biofuels, and bioremediation which are not suitable for common prokaryotes [3]
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