A new low molecular mass alkaline cyclodextrin glucanotransferase from Amphibacillus sp. NRC-WN isolated from an Egyptian soda lake

Background: Cyclodextrin glucanotransferase (CGTase) is one of the most industrially important enzymes used in the commercial production of cyclodextrins (CDs). Alkaliphilic bacteria have attracted much interest in the last few decades because of their ability to produce extracellular enzymes that are active and stable at high pH values. Here, we report the isolation of a new CGTase from alkaliphilic bacteria collected from Egyptian soda lakes and describe the purification and biochemical characterization of this CGTase. Results: Screening for CGTase-producing alkaliphilic bacteria from sediment and water samples collected from Egyptian soda lakes located in the Wadi Natrun valley resulted in the isolation of a potent CGTase-producing alkaliphilic bacterial strain, designated NRC-WN. Strain NRC-WN was belonging to genus Amplibacullus by 16S rDNA sequence analysis (similarity: ca. 98%). Among the tested nitrogen and carbon sources, peptone (0.15%, w/v) and soluble starch (0.4%, w/v) allowed maximal CGTase production by Amphibacillus sp. NRC-WN. CGTase was successfully purified from Amphibacillus sp. NRC-WN up to 159.7-fold through a combination of starch adsorption and anion exchange chromatography, resulting in a yield of 84.7%. SDS-PAGE analysis indicated that the enzyme was purified to homogeneity and revealed an estimated molecular mass of 36 kDa, which makes it one of the smallest CGTases reported in the literature. The purified enzyme exhibited maximum activity at 50oC and was stable up to 70oC, retaining 93% of its initial activity after treatment for 1 hr. Furthermore, Ca2+ ions (10 mM) significantly enhanced the thermal stability of the CGTase. The purified enzyme was active and stable over a wide pH range, showing maximal activity at pH 9.5. The enzyme was significantly stimulated by Zn2+, Ca2+ and Co2+ but was completely inhibited in the presence of Fe3+ and mercaptoethanol. The Km and Vmax values of the purified CGTase were estimated to be 0.0434 mg/ml and 3,333.3 mg \u3b2-CD/ml/min, respectively. \u3b2-CD was the predominant product of starch degradation by the Amphibacillus sp. NRC-WN CGTase, followed by \u3b1-and \u3b3-CDs. Conclusions: A new low molecular mass alkaline CGTase was purified from a newly identified alkaliphilic Amphibacillus sp. NRC-WN isolate from the Egyptian soda lakes. The enzyme showed promising thermal and pH stability and a high affinity toward starch as a natural substrate

On Physical Layer Security in Energy-Efficient Wireless Health Monitoring Applications

In this paper, we investigate a multi-objective optimization framework for secure wireless health monitoring applications. In particular, we consider a legitimate link for the transmission of a vital EEG signal, threatened by a passive eavesdropping attack, that aims at wiretapping these measurements. We incorporate in our framework the practical secrecy metric, namely secrecy outage probability (SOP), which requires only the knowledge of side information regarding the eavesdropper (Ev), instead of completely having its instantaneous channel state information (CSI). To that end, we formulate an optimization problem in the form of maximizing the energy efficiency of the transmitter, while minimizing the distortion encountered at the signal resulting from the compression process prior to transmission, under realistic quality of service (QoS) constraints. The problem is shown to be nonconvex and NP-complete. Towards solving the problem, a branch and bound (BnB)-based algorithm is presented where a ?-suboptimal solution, from the global optimal one, is obtained. Numerical results are conducted to verify the system performance, where it is shown that our proposed approach outperforms similar systems deploying fixed compression policies (FCPs). We successfully meet QoS requirements while optimizing the system objectives, at all channel conditions, which cannot be attained by these FCP approaches. Interestingly, we also show that a target secrecy rate can be practically achieved with nonzero probability, even when the Ev has a better channel condition, on the average, than that for the legitimate receiver.This work was made possible by NPRP grant # NPRP8-408-2-172 from the Qatar National Research Fund (a member of Qatar Foundation).Scopu

Can internal stresses explain the fracture resistance of cusp-replacing composite restorations?

Contains fulltext : 47471.pdf (publisher's version ) (Closed access)The aim of this study was to explore and compare the results of occlusal load application to cusp-replacing composite restorations, studied by means of finite element (FE) analysis and in vitro load tests. A three-dimensional (3D) FE model was created with a set up similar to an in vitro load test that assessed the fatigue resistance of upper premolars with buccal cusp-replacing resin composite restorations. Occlusal load was applied to two geometries (with and without palatal cuspal coverage), and the tooth-restoration interface and composite material stresses were calculated. Subsequently, safety factors were calculated by dividing the material strength values by the obtained stresses. The highest safety factors were observed for the restorations with cuspal coverage. This was consistent with the load test, in which cuspal coverage led to higher fracture resistance. Furthermore, the FE analysis predicted that failure of the tooth-restoration interface is more likely than failure of the composite material. Correspondingly, the load test showed predominantly adhesive failures of the restorations. Although the described test methods did not lead to a complete understanding of the failure mechanism, it can be concluded that the FE analysis provides additional information with regard to the differences in fracture behaviour of these types of restorations