Oxygen availability is the major determinant of the metabolic modes adopted by Escherichia coli. Although much is known about E. coli gene expression and metabolism under fully aerobic and anaerobic conditions, the intermediate oxygen tensions that are encountered in natural niches are understudied. Here, for the first time, the transcript profiles of E. coli K-12 across the physiologically significant range of oxygen availabilities are described. These suggested a progressive switch to aerobic respiratory metabolism and a remodeling of the cell envelope as oxygen availability increased. The transcriptional responses were consistent with changes in the abundance of cytochrome bd and bo and the outer membrane protein OmpW. The observed transcript and protein profiles result from changes in the activities of regulators that respond to oxygen itself or to metabolic and environmental signals that are sensitive to oxygen availability (aerobiosis). A probabilistic model (TFInfer) was used to predict the activity of the indirect oxygen-sensing two-component system ArcBA across the aerobiosis range. The model implied that the activity of the regulator ArcA correlated with aerobiosis but not with the redox state of the ubiquinone pool, challenging the idea that ArcA activity is inhibited by oxidized ubiquinone. The amount of phosphorylated ArcA correlated with the predicted ArcA activities and with aerobiosis, suggesting that fermentation product-mediated inhibition of ArcB phosphatase activity is the dominant mechanism for regulating ArcA activity under the conditions used here.The bacterium and model organism Escherichia coli K-12 has three basic metabolic modes: aerobic respiration, anaerobic respiration, and fermentation (1, 2). There is a hierarchy in which aerobic respiration is preferred to anaerobic respiration, which in turn is preferred to fermentation (1). This hierarchy reflects the relative amounts of energy that can be conserved by these metabolic modes, and oxygen availability is the major signal that governs which metabolic mode is adopted.Many environments, both natural (host intestinal tract) and man-made (bioreactors), are characterized by the presence of oxygen gradients and/or regions of variable oxygen availability (3, 4). Thus, how patterns of gene expression adapt across the range of physiologically relevant oxygen availabilities is important for the efficiency of biotechnological processes that use E. coli as a cell factory and for competitiveness in natural environments (4). However, obtaining reproducible data from E. coli cultures at low oxygen tensions is technically demanding, and the overwhelming majority of the relevant literature reports the results of experiments with fully aerobic or anaerobic cultures. Furthermore, as indicated by Alexeeva et al. (5), in the relatively few attempts to study E. coli grown at intermediate oxygen tensions, it was apparent that neither dissolved oxygen tension nor the gas input to a chemostat accurately describes the responses of the culture to changes in ...
Supplementary data are available at Bioinformatics online.
http://homepages.inf.ed.ac.uk/gsanguin/software.html.
Digital images have become part of everyday life by demonstrating its usability in a variety of fields from education to space research. Confidentiality and security of digital images have grown significantly with increasing trend of information interchange over the public channel. Cryptography can be used as a successful technique to prevent image data from unauthorized access. Keeping the nature of image data in mind, several encryption techniques are presented specifically for digital images, in literature during past few years. These cryptographic algorithms lack a benchmark for evaluation of their performance, cryptographic security and quality analysis of recovered images. In this study, we have designed and developed a benchmark based on all the parameters necessary for a good image encryption scheme. Extensive studies have been made to categories all the parameters used by different researchers to evaluate their algorithms and an optimum benchmark for evaluation is formulated. This benchmark is used to evaluate three image encryption schemes. The results of evaluation have highlighted the specific application areas for these image encryption schemes.
Visible Light Communication (VLC) is a novel optical wireless communication technology which uses Light Emitting Diodes (LEDs) and Photodiodes for coherent detection and very-high-data rate data communication system. The stringent Line of Sight (LoS) requirement in VLC makes it very suitable for Indoor Positioning System (IPS), to be used for autonomous and smart city infrastructure. The current work aims to implement a real time IPS system using VLC link in Network Simulator (NS-3). The VLC module is implemented by modelling real-time attributes of LEDs, optical channel, and the photodiodes. The localization is carried out using trilateration schemes which measures the Received Signal Strength Indication (RSSI) and the Time Difference of Arrival (TDoA) for position estimation of the target. The project is further extended to obtain a comparative analysis between VLC link and other existing technology, Wi-Fi, as far as positioning accuracy and other important performance metrics are concerned. The simulation results show significant improvement for the VLC link over the Wi-Fi link specially for the TDoA scheme accompanied by increasing number of beacon nodes. INDEX TERMSVisible Light communication, IPS, RSSI, TDoA, Trilateration or Multilateration, NS-3 simulator. I. INTRODUCTION Since the inception of RF technologies, there has been a tremendous growth in the telecommunication sector, especially the wireless networks. However, with the increase in demand of RF spectrum, RF spectrum saturation has been observed. The interference between the communication links has also taken a toll [1]. Due to this dilemma, optical communication technologies, i.e., non-RF spectrum technologies, have gained considerable attention of data communication researchers. Amongst optical communication technologies, VLC is relatively a recent data communication that offer extremely high data rate and inherent security [2]. This is because the VLC provides the best of the transmission characteristics with the minimum trade-off. Other salient features include non-penetration to walls, cost effectiveness, vast spectrum of communication, no interference with RF spectrum (430-790THz), and high resolution for localization applications [3]. The communication over a VLC link is highly secure for covert communication due to opacity hindrance because VLC signal cannot pass through walls and other opaque materials.The high transmission speed, safety, low energy consumptions and operating in restricting environments, all provide an edge to VLC over the standard Wireless communication technologies [4]. It is worth-mentioning that although VLC links are very reliable due to the noninterference of RF signals, yet Low Density Parity Check (LDPC) codes are, in general, able to achieve the capacityapproaching performance of a myriad of communication systems. However, the present work does not take into consideration the use of LDPC codes due to the scope of the work [5,6]. The VLC systems use LEDs to transmit wireless data over long distances and support su...
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