Biophotonic sensor for swift detection of malignant brain tissues by using nanocomposite YBa2Cu3O7/dielectric material as a 1D defective photonic crystal.

In the present research work we have theoretically examined the biosensing capabilities of proposed one dimensional defective photonic crystal for swift detection of malignant brain tissues. The transfer matrix formulation and MATLAB computational tool have been used to examine the transmission properties of proposed structure. The identical buffer layers of nanocomposite superconducting material have been used either side of cavity region to enhance the interaction between incident light and different brain tissue samples poured into the cavity region. All the investigations have been carried out under normal incidence to suppress the experimental liabilities involved. We have investigated the biosensing performance of the proposed design by changing the values of two internal parameters (1) the cavity layer thickness (d4) and (2) volume fraction (η) of nanocomposite buffer layers one by one to get the optimum biosensing performance from the structure. It has been found that the sensitivity of the proposed design becomes 1.42607 µm/RIU when the cavity region of thickness 15dd is loaded with lymphoma brain tissue. This value of sensitivity can be further increased to 2.66136 µm/RIU with η = 0.8. The findings of this work are very beneficial for designing of various bio-sensing structures composed of nanocomposite materials of diversified biomedical applications.

Bio-Alcohol Sensor Based on One-Dimensional Photonic Crystals for Detection of Organic Materials in Wastewater.

In this work, we have explored a novel application of one-dimensional (1D) photonic crystals (PCs) as a biomarker for the detection of organic materials in wastewater. The high concentration of organic materials may lead to adverse impact on human life. In order to save human life from these adverse effects, we have investigated the bio-alcohol sensing properties of a 1D multilayer periodic structure (AB)N/C/(AB)N capable of detecting organic materials in wastewater. The proposed structure works on the principle to detect a very small change in the refractive index of the wastewater sample under investigation by means of producing a shift in the position of the defect mode inside the photonic band gap (PBG) of the proposed structure. The transfer matrix method (TMM) has been used to investigate the transmission properties of the proposed design with the help of MATLAB software. We have also studied the effect of changes in the defect layer's thickness, the volume fraction of the nanocomposite material and the incident angle on the sensitivity of our proposed bio-alcohol sensing design. Our bio-alcohol sensor shows a high sensitivity value of 500 nm/RIU and a low detection limit value of 1 × 10-5 RIU. The figure of merit and quality factor values of our bio-alcohol sensor are 5 × 103 and 5.236 × 103, respectively. The damping rate of the design is ξ=95.4927×10-5.

Microbial Cell Factories for Diol Production.

Diols are compounds with two hydroxyl groups and have a wide range of appealing applications as chemicals and fuels. In particular, five low molecular diol compounds, namely 1,3-propanediol (1,3-PDO), 1,2-propanediol (1,2-PDO), 2,3-butanediol (2,3-BDO), 1,3-butanediol (1,3-BDO), and 1,4-butanediol (1,4-BDO), can be biotechnologically produced by direct microbial bioconversion of renewable materials. In this review, we summarize recent developments in the microbial production of diols, especially regarding the engineering of typical microbial strains as cell factory and the development of corresponding bioconversion processes.

Comparative physiological study of the wild type and the small colony variant of Pseudomonas aeruginosa 20265 under controlled growth conditions.

Small-colony variants (SCVs) of Pseudomonas aeruginosa are often found in chronically infected airways of patients suffering from cystic fibrosis. These slow-growing morphological variants have been associated with persistent and antibiotic-resistant infections. Nevertheless, the behavior of SCVs under varied availability of O2 and iron, two key variables relevant to the lung environment of CF patients and pathogenicity of P. aeruginosa, has not been systematically studied so far. In this work, the effects of O2 and iron were comparatively studied for a CF P. aeruginosa wild type (WT) strain and its SCV phenotype in a real-time controlled cultivation system. Significant differences in the behavior of these strains were observed and quantified. In general, SCV exhibited a higher fitness than the WT toward aerobic conditions. Under iron rich condition, and despite less release of total extracellular proteins, absence of flagellin and lower siderophore production, the SCV cells grown at fully aerobic conditions showed a higher specific growth rate and a significantly higher cytotoxicity in comparison with the WT cells. The strains behaved also differently towards iron limitation. The phenomena of limited O2 transfer from the gas to the liquid phase and enhancement of formation of virulence factors under conditions of iron limitation were much more profound in the SCV culture than in the WT culture. These results have important implications for better understanding the pathogenicity of P. aeruginosa and its small-colony variants.

Substrate-limited co-culture for efficient production of propionic acid from flour hydrolysate.

Propionic acid is presently mainly produced by chemical synthesis. For many applications, especially in feed and food industries, a fermentative production of propionic acid from cheap and renewable resources is of large interest. In this work, we investigated the use of a co-culture to convert household flour to propionic acid. Batch and fed-batch fermentations of hydrolyzed flour and a process of simultaneous saccharification and fermentation were examined and compared. Fed-batch culture with substrate limitation was found to be the most efficient process, reaching a propionic acid concentration of 30 g/L and a productivity of 0.33 g/L*h. This is the highest productivity so far achieved with free cells on media containing flour hydrolysate or glucose as carbon source. Batch culture and culture with controlled saccharification and fermentation delivered significantly lower propionic acid production (17-20 g/L) due to inhibition by the intermediate product lactate. It is concluded that co-culture fermentation of flour hydrolysate can be considered as an appealing bioprocess for the production of propionic acid.

Alterations in the formation of lipopolysaccharide and membrane vesicles on the surface of Pseudomonas aeruginosa PAO1 under oxygen stress conditions.

It has been postulated that phenotypic variation in the relative expression of two chemically distinct types of lipopolysaccharide (LPS), a serotype-specific LPS (B-band) and a common antigen LPS (A-band) in Pseudomonas aeruginosa is an important mechanism enabling this opportunistic pathogen to alter its surface characteristics to mediate adhesion and to survive under extreme conditions. To further investigate this, the relative expression levels of the two distinct types of LPS in P. aeruginosa PAO1 were investigated with cells grown in a chemostat at different dissolved oxygen tensions (pO(2)). The A-band LPS was constitutively expressed as pO(2) was increased from nearly zero to 350 % of air saturation. In contrast, the B-band LPS showed a remarkable increase with increased pO(2). Almost no B-band LPS was found in cells grown at a pO(2) of less than 3 % of air saturation. Electron microscopic examination of cells revealed increased formation of membrane vesicles (MVs) on the surface of P. aeruginosa PAO1 under oxygen stress conditions. The toxicity of the supernatant of P. aeruginosa cultures to the growth of a hybridoma cell line significantly increased in samples taken from oxygen-stressed steady-state cultures. Furthermore, studies of adhesion in a continuous-flow biofilm culture revealed an increased adhesiveness for hydrophilic surfaces in P. aeruginosa PAO1 grown at a higher pO(2). The oxygen-dependent alterations of cell-surface components and properties observed in this work provide a possible explanation for the emergence of P. aeruginosa lacking the B-band LPS in chronically infected cystic fibrosis patients. The results are also useful for understanding the processes involved in the formation of MVs in P. aeruginosa.

Bacterial alginate: physiology, product quality and process aspects.

Alginate, a copolymer of beta-D-mannuronic acid and alpha-L-guluronic acid and currently commercially produced from the marine brown algae, can also be biologically produced by bacteria such as Azotobacter vinelandii, A. chroococcum and several species of Pseudomonas. The ever-increasing applications of this polymer in the food and pharmaceutical sectors have led to continuing research interest aimed at better understanding the metabolic pathways, the physiological or biological function of this polymer, the regulation of its formation and composition, and optimising the microbial production process. These aspects are reviewed here, with particular attention to alginate formation in the soil bacterium A. vinelandii. In addition, the biotechnological and industrial applications of alginate are summarised.

Effect of oxygen on formation and structure of Azotobacter vinelandii alginate and its role in protecting nitrogenase.

The activity of nitrogenase in the nitrogen-fixing bacterium Azotobacter vinelandii grown diazotrophically under aerobic conditions is generally considered to be protected against O(2) by a high respiration rate. In this work, we have shown that a high rate of respiration is not the prevailing mechanism for nitrogenase protection in A. vinelandii grown in phosphate-limited nitrogen-free chemostat culture. Instead, the formation of alginate appeared to play a decisive role in protecting the nitrogenase that is required for cell growth in this culture. Depending on the O(2) tension and cell growth rate, the formation rate and composition of alginate released into the culture broth varied significantly. Furthermore, transmission electron microscopic analysis of cell morphology and the cell surface revealed the existence of an alginate capsule on the surface of A. vinelandii. The composition, thickness, and compactness of this alginate capsule also varied significantly. In general, increasing O(2) tension led to the formation of alginate with a higher molecular weight and a greater L-guluronic acid content. The alginate capsule was accordingly thicker and more compact. In addition, the formation of the alginate capsule was found to be strongly affected by the shear rate in a bioreactor. Based on these experimental results, it is suggested that the production of alginate, especially the formation of an alginate capsule on the cell surface, forms an effective barrier for O(2) transfer into the cell. It is obviously the quality, not the quantity, of alginate that is decisive for the protection of nitrogenase.

Effect of nutrients on alginate synthesis in Azotobacter vinelandii and characterization of the produced alginate.

The role of nutrients on alginate production by Azotobacter vinelandii was studied in batch cultures. The largest amount of bacterial alginate was obtained in presence of: 0.3 g/l MgSO4.7H2O. 0.4 g/l NaCl, 42 mg/l CaCl2.2H2O,.4 mg/l KH2PO4, 16 mg/l K2HPO4, 2.5 mg/l FeSO4.7H2O, 2.9 mg/l H3BO3, 2 mg/l ZnSO4.7H2O, 2 mg/l Na2MoO4.2H2O, 0.3 mg/l CuSO4.5H2O, 0.2 mg/l MnCl2.4H2O. Alginate production was not enhanced by natural additives or inducing agents, except for acetate, which increased alginate yield. The pure alginate contained 0.36% ash and 0.4% protein. It is similar to algal alginate, but it has an extra acetyl group. It contains 69.5% M-M block, 27.5% M-G block and 3% G-G block.