Synthesis of Silica-coated Iron Oxide Nanoparticles: Preventing Aggregation without Using Additives or Seed Pretreatment.

The Stober process is frequently used to prepare silica-coated iron oxide nanoparticles. This is usually achieved by seeding a reaction mixture consisting of water, ethanol and a catalyst with iron oxide particles and adding a silica precursor. The hydrolysis and condensation of precursor monomers results in the deposition of a silica layer on iron oxide particles. However, this process is accompanied by an increase in the ionic strength of the medium which promotes the rapid aggregation of iron oxide particles. A number of methods have been developed to prevent seed aggregation during the coating process. The majority of these methods include a pretreatment step in which the surface of iron oxide particles is modified in a manner that increases their stability in aqueous solutions. Here we suggest that by decreasing the initial concentration of the catalyst for a short period to minimize nucleation by reducing precursor hydrolysis rate and then gradually increasing the concentration to the optimum level to allow silica formation to proceed normally it may be possible to prevent aggregation without surface modification. The properties of the resulting nanoparticles as analyzed by transmission electron microscopy and magnetometry as well as their efficiency at extracting genomic DNA from different bacterial strains compared to that of a commercial extraction kit are also reported.

Screening for Type II L-Asparaginases: Lessons from the Genus Halomonas.

Among the two types of bacterial L-asparaginases, only type II enzymes have been used in the treatment of acute lymphoblastic leukemia owing to their higher affinity for L-asparagine. However, current screening media used for the isolation of L-asparaginase-producing microorganisms do not discriminate between the two types of L-asparaginase. During an optimization study conducted to increase L-asparaginase production by environmental Halomonas isolates, it was noticed that the pattern of L-asparaginase production in response to variations in glucose concentration varied between different isolates suggesting that they differ in their ability to produce type II L-asparaginases, an observation that was confirmed by further experiments. Bioinformatics analysis of available Halomonas whole genome sequences revealed that indeed some species of this genus possess both L-asparaginase types while others possess only type I enzymes. By comparing the growth pattern of these isolates on different media, we propose that by omitting glucose, reducing the concentration of L-asparagine and providing an alternative nitrogen source in L-asparaginase screening media it may be possible to differentiate between type I and type II activities.

L-Asparaginase Activity in Cell Lysates and Culture Media of Halophilic Bacterial Isolates.

The objective of this study was to isolate halophilic bacteria with the ability to produce intracellular or extracellular L-asparaginase. A total number of 120 halophilic bacteria were isolated from 17 different saline habitats of Iran including salt lakes, wetlands, brine springs and deserts. Among these, 68 were able to grow in the presence of 1.5 M NaCl and 52 demonstrated the ability to grow in the selection medium containing 3.5 M NaCl. None of the isolates appeared to produce appreciable amounts of extracellular L-asparaginase. Among the isolates that produced intracellular L-asparaginase, 5 moderate and 1 extreme halophiles were selected for further study based on their observed activity level. The moderately halophilic isolates were shown to belong to the genus Halomonas while the extreme halophile was identified as a member of the genus Aidingimonas.

From bacteria to human: a journey into the world of chitinases.

Chitinases, the enzymes responsible for the biological degradation of chitin, are found in a wide range of organisms from bacteria to higher plants and animals. They participate in numerous physiological processes such as nutrition, parasitism, morphogenesis and immunity. Many organisms, in addition to chitinases, produce inactive chitinase-like lectins that despite lacking enzymatic activity are involved in several regulatory functions. Most known chitinases belong to families 18 and 19 of glycosyl hydrolases, however a few chitinases that belong to families 23 and 48 have also been identified in recent years. In this review, different aspects of chitinases and chi-lectins from bacteria, fungi, insects, plants and mammals are discussed.

Optimization of Chitinase Production by Bacillus pumilus Using Plackett-Burman Design and Response Surface Methodology.

A soil bacterium capable of degrading chitin on chitin agar plates was isolated and identified as Bacillus pumilus isolate U5 on the basis of 16S rDNA sequence analysis. In order to optimize culture conditions for chitinase production by this bacterium, a two step approach was employed. First, the effects of several medium components were studied using the Plackett-Burman design. Among various components tested, chitin and yeast extract showed positive effect on enzyme production while MgSO4 and FeSO4 had negative effect. However, the linear model proved to be insufficient for determining the optimum levels for these components due to a highly significant curvature effect. In the second step, Box-Behnken response surface methodology was used to determine the optimum values. It was noticed that a quadratic polynomial equation fitted he experimental data appropriately. The optimum concentrations for chitin, yeast extract, MgSO4 and FeSO4 were found to be 4.76, 0.439, 0.0055 and 0.019 g/L, respectively, with a predicted value of chitinase production of 97.67 U/100 mL. Using this statistically optimized medium, the practical chitinase production reached 96.1 U/100 mL.

Purification and characterization of two extracellular endochitinases from Massilia timonae.

Two extracellular chitinases (designated as Chi-56 and Chi-64) produced by Massilia timonae were purified by ion-exchange chromatography, ammonium sulfate precipitation, and gel-filtration chromatography. The molecular mass of Chi-56 was 56 kDa as determined by both SDS-PAGE and gel-filtration chromatography. On the other hand, Chi-64 showed a molecular mass of 64 kDa by SDS-PAGE and 28 kDa by gel-filtration chromatography suggesting that its properties may be different from those of Chi-56. The optimum temperature, optimum pH, pI, K(m), and V(max) of Chi-56 were 55 degrees C, pH 5.0, pH 8.5, 1.1 mg mL(-1), and 0.59 micromol microg(-1)h(-1), respectively. For Chi-64, these values were 60 degrees C, pH 5.0, pH 8.5, 1.3 mg mL(-1), and 1.36 micromol microg(-1)h(-1), respectively. Both enzymes were stimulated by Mn(2+) and inhibited by Hg(2+), and neither showed exochitinase activity. The N-terminal sequences of Chi-56 and Chi-64 were determined to be Q-T-P-T-Y-T-A-T-L and Q-A-D-F-P-A-P-A-E, respectively.

MICROALGAL BIOTRANSFORMATION OF STEROIDS(1).

Microbial biotransformation of steroids is not a new concept, but most studies in this field have focused on fungal and bacterial systems. Microalgae, despite their photosynthetic ability and immense biodiversity, have not received much attention in this aspect until recently. Since the publication of the first article on microalgal biotransformation of steroids about 20 years ago, there have been many reports describing different modifications, including hydroxylation, reduction, side-chain degradation, and isomerization introduced by these microorganisms on estrane, androstane, and pregnane derivatives. On the other hand, the development of new large-scale cultivation systems, the adaptation of existing fermentation techniques to microalgae, and the introduction of microalgal genetic manipulation methods have made these organisms promising candidates for a wide range of biotechnological processes, including biotransformations. In this review, we have summarized the steroid transformation patterns of several microalgal strains and present a perspective of the future trends in microalgal biotechnology, including the possibility of adapting relatively new techniques, such as organic media catalysis and cell immobilization, to this specific field.