Unified description of size effects of transport properties of liquids flowing in nanochannels

The present work connects transport properties of simple fluids flowing in nanochannels: the diffusion coefficient, the shear viscosity and the thermal conductivity. We used non-equilibrium molecular dynamics (NEMD) simulations of liquid argon flowing in a nanochannel formed by krypton walls, macroscopically equivalent to the planar Poiseuille flow, at constant temperature. All properties approach bulk values as the channel width increases. As the channel width decreases, the transport properties change dramatically: the diffusion coefficient decreases with the channel width, the shear viscosity increases with the channel width and the thermal conductivity increases with the channel width. The novel result of this work is that, if the size effect of one of the transport properties (say the diffusion coefficient) is known, then all the others can be estimated from results that apply to classic fluid mechanics.     

Archaeal nucleosome positioning by CTG repeats

DNA shape recognition determines the preferred binding sites for sequence-independent DNA binding proteins, and here we document that archaeal histones assemble archaeal nucleosomes in vitro centered preferentially within (CTG)6 and (CTG)8 repeats, close to junctions with flanking mixed-sequence DNA. Archaeal nucleosomes were not positioned by (CTG)4-, (CTG)5-, or (CTG)3AA(CTG)3-containing DNA sequences. The features of CTG repeat-containing sequences that direct eucaryal nucleosome positioning may also be similarly recognized by archaeal histones.     

Membrane-bound electron transfer chain of the thermohalophilic bacterium Rhodothermus marinus: a novel multihemic cytochrome bc, a new complex III

Rhodothermus marinus, a thermohalophilic bacterium, has a unique electron-transfer chain, containing, besides a cbb3 and a caa3 terminal oxidases, a novel cytochrome bc complex [Pereira, M. M., Carita, J. N., and Teixeira, M. (1999) Biochemistry 38, 1268-1275]. The membrane-bound iron-sulfur centers of this bacterium were studied by electron paramagnetic resonance (EPR) spectroscopy, leading to the identification of its main electron-transfer complexes. The resonances typical for the Rieske-type centers are not detected. Clusters S1 and S3 from succinate dehydrogenase were identified; interestingly, center S3 is shown to be present in two different conformations, with g values at 2.035, 2.009, and 2.001 and at 2.025, 2.002, and 2.000. Upon addition of NADH and dithionite, EPR signals assigned to resonances characteristic of binuclear and tetranuclear clusters develop and are attributed to the iron-sulfur centers of complexes I and II. A high-potential iron-sulfur protein- (HiPIP-) type center previously detected in the membranes of this bacterium [Pereira et al. (1994) FEBS Lett. 352, 327-330] is shown to belong indeed to a canonical HiPIP. This protein was purified and extensively characterized. It is a small water-soluble protein of approximately 10 kDa, containing a single [4Fe-4S]3+/2+ cluster. The reduction potential, determined by EPR redox titrations in intact and detergent-solubilized membranes as well as by cyclic voltammetry in solution, has a pH-independent value of 260 +/- 20 mV, in the range 6-9. In vitro reconstitution of the R. marinus electron-transfer chain shows that the HiPIP plays a fundamental role in the chain, as the electron shuttle between R. marinus cytochrome bc complex and the caa3 terminal oxidase, being thus simultaneously identified a HiPIP reductase and a HiPIP oxidase.     

Evaluation of Changes in Listeria monocytogenes Populations on Frankfurters at Different Stages from Manufacturing to Consumption

ABSTRACT: This study evaluated the fate of inoculated Listeria monocytogenes on frankfurters stored under conditions simulating those that may be encountered between manufacturing and consumption. Frankfurters with or without 1.5% potassium lactate and 0.1% sodium diacetate (PL/SD) were inoculated (1.8 ± 0.1 log CFU/cm²) with a 10‐strain composite of L. monocytogenes, vacuum‐packaged, and stored under conditions simulating predistribution storage (24 h, 4 °C), temperature abuse during transportation (7 h, 7 °C followed by 7 h, 12 °C), and storage before purchase (60 d, 4 °C; SBP). At 0, 20, 40, and 60 d of SBP, samples were exposed to conditions simulating delivery from stores to homes or food establishments (3 h, 23 °C), and then opened or held vacuum‐packaged at 4 or 7 °C for 14 d (SHF). Pathogen counts remained relatively constant on frankfurters with PL/SD regardless of product age and storage conditions; however, they increased on product without antimicrobials. In vacuum‐packaged samples, during SHF at 4 °C, the pathogen grew faster (P < 0.05) on older product (20 d of SBP) compared to product that was fresh (0 d of SBP); a similar trend was observed in opened packages. At 7 °C, the fastest growth (0.35 ± 0.02 log CFU/cm²/d) was observed on fresh product in opened packages; in vacuum‐packages, growth rates on fresh and aged products were similar. By day 40 of SBP the pathogen reached high numbers and increased slowly or remained unchanged during SHF. This information may be valuable in L. monocytogenes risk assessments and in development of guidelines for storage of frankfurters between package opening and product consumption.     

Incidence of Salmonella on beef carcasses relating to the U.S. meat and poultry inspection regulations.

This article is part of a major study designed to collect baseline contamination data by sampling beef carcasses in seven slaughtering plants (four steer-heifer and three cow-bull plants) during both a dry season (November to January) and a wet season (May to June). Samples (n = 30) were excised from each of three carcass anatomical sites (brisket, flank, and rump) at each of three points in the slaughtering chain (pre-evisceration, following final carcass washing, after 24-h carcass chilling). A total of 3,780 samples (100 cm2 each) were analyzed for presence of Salmonella; aerobic plate counts, total coliform counts, and Escherichia coli counts were also made. After 24-h chilling, average incidence (expressed as a percentage) of Salmonella in the brisket, flank, and rump samples, respectively, for steer-heifer carcasses was 0.8+/-1.7, 0, and 2.5+/-5.0 for the wet season and 0.8+/-1.7, 0, and 0 for the dry season; the corresponding percentages for cowbull carcasses were 4.4+/-2.0, 2.2+/-3.9, and 1.1+/-1.9 for the wet season and 2.2+/-3.9, 1.1+/-1.9, and 0 for the dry season. Depending on plant and season, ranges of probabilities of chilled steer-heifer carcasses passing the U.S. regulatory requirements for Salmonella contamination were 0.24 to 1.0 for the brisket, 1.0 for the flank, and 0.002 to 1.0 for the rump; the corresponding ranges for the chilled cow-bull carcasses were 0.25 to 1.0, 0.25 to 1.0, and 0.70 to 1.0. When the number of positive brisket, flank, and rump samples were combined, the probabilities of passing the regulatory requirements were 0.242 to 1.0 and 0.772 to 1.0 for the wet and dry seasons, respectively, in steer-heifer plants and 0.368 to 0.974 and 0.865 to 1.0 in cow-bull plants. Correlation coefficients of aerobic plate counts, total coliform counts, and E. coli counts with Salmonella incidence were higher (P< or =0.05) for cow-bull samples that had increased incidence of the pathogen when compared to steer-heifer samples.