---

The biosynthesis of nanoparticles (NPs) has been proposed due to its fast, clean, safe, and cost-effective production and being efficient alternative to conventional physicochemical methods. This study aimed to isolate and identify aquatic yeast strains for their potential to form Zinc oxide nanoparticles (ZnONPs). A yeast strain, NS02, with high tolerance against zinc ion (5.25 mM) was isolated using the enrichment technique and was selected as efficient candidate for the biosynthesis of ZnONPs under cell-free extract (CFE) strategy. The preliminary evaluation on the formation of ZnONPs was performed by visual observation and UV-visible absorption spectra of the biosynthesized ZnONPs. The morphology, size and elemental distribution of the nanoparticles were determined by Field emission scanning electron microscopy (FESEM) equipped with energy-dispersive X-ray (EDX). X-ray diffractometer (XRD) was used to identify the crystalline phase of the ZnONPs. Antibacterial activity of ZnONPs against pathogenic bacteria isolated from the clinical specimens was investigated using agar well diffusion method. The isolate NS02 was characterized based on their morphological properties and amplification the ITS-5.8S-ITS2 rDNA regions. The present study pioneered the capabilities of the native aquatic strain Rhodotorula pacifica for the extracellular synthesis of ZnONPs with CFE strategy. The biosynthesized ZnONPs had a growth inhibitory effect all tested clinical isolates due to their nanometric size and well-defined dispersity. This investigation is attempted to indicate the novel microbial sources of aquatic yeasts as biological plant in the synthesis of ZnONPs with antimicrobial activity under cell-free extract strategy.
 

---

This study investigated the potential of aquatic bacteria for their ability as a biocatalyst to synthesized Fe2O3 nanoparticles using iron precursor, FeCl3. A total of 25 aquatic bacterial strains were isolated in trypticase soy agar plus 10 mM FeCl3 with selective enrichment technique. Among the bacterial strains evaluated, NV06 was the only strain able to synthesize Fe2O3 nanoparticles extracellularly. The strain NV06 was identified as Alcaligenes sp., on the basis of phenotypic and molecular characteristics. Extracellular synthesis of Fe2O3 nanoparticles by this strain was investigated under the optimal conditions. The biosynthesized Fe2O3 nanoparticles were characterized using UV–visible spectrophotometry (UV-Vis), Scanning electron microscopy (SEM), Energy-dispersive X-ray spectroscopy (EDX), and Fourier transform infrared (FTIR) spectroscopy. The results showed that cell-free extract (CFE) of the bacterium strain can produce the rod-shaped Fe2O3 nanoparticles with mean edge lengths of 80.2 nm and mean diameters of 25.5 nm, after being exposed to FeCl3 solution (10 mM), at an optimum pH of 6 and an optimum temperature of 28 °C, after 96 hours of incubation at 150 rpm. This is the first report on the extracellular biosynthesis of Fe2O3 nanoparticles using the genus of Alcaligenes under the CFE strategy. It could be speculated that the results of the study can hopefully introduce the inherent capabilities of aquatic microbes as safe, simple, and effective biocatalysts in the production of Fe2O3 nanoparticles.