Unexpected differential metabolic responses of Campylobacter jejuni to the abundant presence of glutamate and fucose

Introduction: Campylobacter jejuni is the leading cause of foodborne bacterial enteritis in humans, and yet little is known in regard to how genetic diversity and metabolic capabilities among isolates affect their metabolic phenotype and pathogenicity. Objectives: For instance, the C. jejuni 11168 strain can utilize both l-fucose and l-glutamate as a carbon source, which provides the strain with a competitive advantage in some environments and in this study we set out to assess the metabolic response of C. jejuni 11168 to the presence of l-fucose and l-glutamate in the growth medium. Methods: To achieve this, untargeted hydrophilic liquid chromatography coupled to mass spectrometry was used to obtain metabolite profiles of supernatant extracts obtained at three different time points up to 24 h. Results: This study identified both the depletion and the production and subsequent release of a multitude of expected and unexpected metabolites during the growth of C. jejuni 11168 under three different conditions. A large set of standards allowed identification of a number of metabolites. Further mass spectrometry fragmentation analysis allowed the additional annotation of substrate-specific metabolites. The results show that C. jejuni 11168 upon l-fucose addition indeed produces degradation products of the fucose pathway. Furthermore, methionine was faster depleted from the medium, consistent with previously-observed methionine auxotrophy. Conclusions: Moreover, a multitude of not previously annotated metabolites in C. jejuni were found to be increased specifically upon l-fucose addition. These metabolites may well play a role in the pathogenicity of this C. jejuni strain.</p

Silicon carbide (SiC) membrane nanomechanical resonators with multiple vibrational modes

We report on experimental demonstration of a new type of nanomechanical resonators based on very thin silicon carbide (SiC) square membranes. An optical interferometry with a radio-frequency two-port measurement scheme enables sensitive and efficient detection of many vibrational modes of the membranes. Membranes with sizes up to 1mm × 1mm and thicknesses down to t ≤ 500nm, offer very high aspect ratios and compelling resonance spectra of multiple-mode operations from kHz range to the HF (3-30MHz) band. Typical resonances have Q's ∼ 800-30000 at room temperature and in vacuum of ∼20mTorr. Some high-Q modes exhibit fairly strong nonlinear effects. © 2011 IEEE.link_to_subscribed_fulltex

Electrostatically driven touch-mode poly-SiC micro speaker

This paper presents an electrostatically driven microspeaker utilizing a SiC membrane operating in the touch-mode configuration. The device is formed using conventional wafer bonding to hermetically seal a low-stress, heavily-doped polycrystalline 3C-SiC (poly-SiC) membrane to a bulk micromachined silicon back-plate containing a thin oxide insulating layer. The bonding process is done in high vacuum, causing the poly-SiC membrane to flex down into contact with the back-plate when exposed to atmospheric pressure. Sound Pressure Level (SPL) measurements were recorded for a device with a poly-SiC membrane thickness of 1μm, a diameter of 800μm, and a diaphragm/back-plate spacing of 8μm. At a distance of 10mm, a maximum SPL of 73 dB was found at a frequency of 16.59 kHz. © 2007 IEEE.link_to_subscribed_fulltex