Physicochemical and biological characteristics of the nanostructured polysaccharide-iron hydrogel produced by microorganismKlebsiella oxytoca

Abstract

There is an increasing interest in the nanostructured polysaccharide-iron hydrogel produced by Klebsiella oxytoca. Critical physicochemical and biological characteristics of these nanostructures should be revealed for biomedical applications. Accordingly, an iron reducing strain K. oxytoca, which synthesizes biogenic polysaccharide-iron hydrogel nanoparticles, known as Fe (III)-exopolysaccharide (Fe-EPS) was isolated from a mineral spring. For microbiological identification purpose 16S rRNA sequence analysis and different morphological, physiological, and biochemical characteristics of the isolate were studied. Critical physicochemical and biological characteristics of the produced Fe-EPS were evaluated using transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectroscopy, X-ray crystallography (XRD), vibrating sample magnetometer (VSM). In addition, for the first time, Fe-EPS which synthesized by K. oxytoca was evaluated by dynamic light scattering (DLS), thermo gravimetric analysis (TGA), and cytotoxicity assay. TEM micrographs showed that the biogenic Fe-EPS is composed of ultra-small (about 1.8 nm) iron oxide nanoparticles (IONs) which are trapped in a polysaccharide matrix. The matrix was about 17% (w/w) of Fe-EPS total weight and provided a large negative charge of -71 mV. Interestingly, Fe-EPS showed a growth promotion effect on hepatocarcinoma cell line (Hep-G2) and 36% increase in the percentage of viability was observed by 24 h exposure to 500 μg ml Fe-EPS.

Iron-Reducing Bacteria and Iron Nanostructures

“…This nanocomposite of exopolysaccharide and iron nanoparticles usually forms a shell with high electron density around the bacterial cells. This shell can be seen as a dark hollow in the transmission electron micrographs (Figure 3) [19].…”

“…Iron minerals which are used as electron acceptor by IRB can give color to bacterial cells, for instance using fumarate as the electron acceptor will give a red color to cells [6]. Klebsiella oxytoca cells which grown on the ferric citrate agar media produce colonies with a metallic shine (Figure 2) [19]. However, it is not universal rule and the red color of some strains of IRB such as Geobacter bremensis and Geobacter pelophilus is due to the presence of c-type cytochromes [6].…”

“…30 mM, pH 7.0). The media are usually enriched with vitamins and trace elements [19][20][21]. For instance, some researchers have used a vitamin and mineral mixture enriched media for cultivation of Klebsiella oxytoca.…”

“…For instance, some researchers have used a vitamin and mineral mixture enriched media for cultivation of Klebsiella oxytoca. The media was supplemented with 50 mM of ferric citrate which provides ferric ions as electron acceptor and also citrate as organic substrate for fermentation [10,19]. The bacteria consume citrate as energy and carbon sources in anaerobic culture condition [8][9][10].…”

“…Nanocrystals have large surface to volume ratio which results in large reactive surface areas for biochemical reactions and hence increase the bioavailability of iron compounds. The surface structure of KCl, 0.1 g; NaH 2 PO4, 1 g; NH 4 Cl, 1.5 g; NaHCO 3 , 2.5 g; ferric citrate, 0.5 mM; mineral solution, 10 ml; vitamin solution, 10 ml [19] NaHCO 3 , 2.5 g, NH 4 Cl, 1.5 g, NaH 2 PO 4 , 0.6 g, KCl, 0.1 g, ferric citrate, 50 mM; vitamin mixture, 10 mL; mineral mixture, 10 mL [10] iron nanoparticles differs from those of larger crystallites which leads to altered reactivity or varied crystal chemistry [44]. For instance, the size-dependent bioavailability of hematite (α-Fe 2 O 3 ) nanoparticles to obligate aerobic Pseudomonas mendocina bacteria was examined by using the natural siderophore-producing wild type strain and a siderophore mutant strain.…”