In this study, the metallothionein gene of Candida albicans (C. albicans) was assembled by polymerase chain reaction (PCR), inserted into pUC19 vector, and further transformed into Escherichia coli (E. coli) DH5α cells. The capacity of these recombinant E. coli DH5α cells to synthesize silver nanoparticles was examined. Our results demonstrated that the expression of C. albicans metallothionein in E. coli promoted the bacterial tolerance to metal ions and increased yield of silver nanoparticle synthesis. The compositional and morphological analysis of the silver nanoparticles revealed that silver nanoparticles synthesized by the engineered E. coli cells are around 20 nm in size, and spherical in shape. Importantly, the silver nanoparticles produced by the engineered cells were more homogeneous in shape and size than those produced by bacteria lack of the C. albicans metallothionein. Our study provided preliminary information for further development of the engineered E. coli as a platform for large-scale production of uniform nanoparticles for various applications in nanotechnology. studies have been seeking to integrate MTs in creating biological platforms for the production of metal NPs. Engineered bacteria expressing MT and/or phytochelatins have been shown to be able to produce diverse nanoparticles [9][10][11].A critical aspect in developing a microbial platform for NP synthesis is choosing a proper host microorganism. It is ideal that a biofactory can make NPs with consistent properties for their applications in various field of nanotechnology. Many types of microorganism have been shown to be able to synthesize various metal NPs, but with diverse properties [12][13][14][15][16]. In addition, the conditions for cultivation and maintenance of microorganisms vary for different species [14][15][16]. Among the microorganisms able to serve as potential biofactories for metal NP synthesis, the readily available bacteria, E. coli, is of particular interest, due to the relatively easy and simple procedures to grow, maintain and manipulate them in the lab. The potential of engineered E. coli as a common platform for synthesis of diverse NP has been explored; however, the efficiency of NP synthesis by the engineered bacteria and the potential to upgrade to large scale NP production were not examined [9][10][11].The goal of this study was to provide preliminary evidence for exploiting engineered E. coil as a platform for the large-scale production of metal NPs with controlled morphological properties. In this study, we chose C. albicans MT as a target protein and transferred a PCR-assembled C. albicans MT gene into E. coli DH5α cells to examine whether expression of C. albicans MT in E. coli would improve bacterial NP synthesis.Compared to E. coli MT, which has four cysteine out of 56 residues (7.1%), the C. albicans MT has a relatively high content of cysteine residues (15.8%). Importantly, the C. albicans has four repeats of Cys-Xaa-Cys presumably for binding metal ions, such as copper [17,18]. To examine whether the...
Selenium is an essential micronutrient for all mammals and plays an important role in maintaining human physiological functions. Selenium nanoparticles (SeNPs) have been shown to demonstrate antioxidant and antimicrobial activity. The objective of this study was to explore whether SeNPs have the potential to be used as food preservatives with which to reduce food spoilage. SeNPs were synthesized through ascorbic acid reduction of sodium selenite (Na2SeO3) in the presence of bovine serum albumin (BSA) as a capping and stabilizing agent. The chemically synthesized SeNPs had a spherical conformation with an average diameter of 22.8 ± 4.7 nm. FTIR analysis confirmed that the nanoparticles were covered with BSA. We further tested the antibacterial activity of these SeNPs against ten common food-borne bacteria. A colony-forming unit assay showed that SeNPs exhibited inhibition on the growth of Listeria Monocytogens (ATCC15313) and Staphylococcus epidermidis (ATCC 700583) starting at 0.5 µg/mL, but higher concentrations were required to slow down the growth of Staphylococcus aureus (ATCC12600), Vibrio alginolyticus (ATCC 33787), and Salmonella enterica (ATCC19585). No inhibition was observed on the growth of the other five test bacteria in our study. Our data suggested that the chemically synthesized SeNPs were able to inhibit the growth of some food-borne bacteria. The size and shape of SeNPs, method of synthesis, and combination of SeNPs with other food preservatives should be considered when SeNPs are to be used for the prevention of bacteria-mediated food spoilage.
Extracts from plants continue to be a vital source of medicines, Ocimum, (family Labiatae) is well known for treatment of a wide range of human illnesses. This study evaluates the extraction methods best suited for the determination of the antimicrobial potential of basil. The methanolic extract of O. gratissimum species had the highest yield (1.48±1.48%), while the essential oil of O. tenuiflorum had the lowest (0.19±0.30%). Comparison of methanolic extracts of different accessions, O.tenuiflorum (MSR1), O.basilicum (PI 172996) showed a growth reduction of 74%, for S. pyogenes, 91% for E. coli respectively; while essential oils of O. basilicum (PI 358472) had a growth reduction of 57% for S. pyogenes, 72% for E. coli. The chloroform extracts exhibited little or no inhibitory effects. In conclusion, the methanolic extracts, and essential oils were equally effective against the tested bacteria. Ocimum species may be used as an alternative source in the search for agents to treat bacteria.
Phytochelatins, the enzymatic products of phytochelatin synthase, play a principal role in protecting the plants from heavy metal and metalloid toxicity due to their ability to scavenge metal ions. In the present study, we investigated the capacity of soluble intracellular extracts from E. coli cells expressing R. tropici phytochelatin synthase to synthesize gold nanoparticle. We discovered that the reaction mediated by soluble extracts from the recombinant E. coli cells had a higher yield of gold nanoparticles, compared to that from the control cells. The compositional and morphological properties of the gold nanoparticles synthesized by the intracellular extracts from recombinant cells and control cells were similar. In addition, this extracellular nanoparticle synthesis method produced purer gold nanoparticles, avoiding the isolation of nanoparticles from cellular debris when whole cells are used to synthesize nanoparticles. Our results suggested that phytochelatins can improve the efficiency of gold nanoparticle synthesis mediated by bacterial soluble intracellular extracts, and the potential of extracellular nanoparticle synthesis platform for the production of nanoparticles in large quantity and pure form is worth further investigation.
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