Escherichia coli sentenced to death by heat stress : reaching out for the last functional genes

Escherichia coli K12 was used as a model to investigate physiological and molecular changes during cell adaptation and survival to cooking temperatures used in food industries. Bacteria grown to stationary phase in BHI broth were heated at 58°C or 60°C until a process lethality value (F70 10) of 2 or 3 was reached, or until an internal core temperature of 71°C was attained. Growth and cell integrity were evaluated after heating. Transcriptional modifications were analyzed by microarrays and expression of heat-shock genes was quantified by qPCR. Only cells heated at 58°C F=2 were still able to grow in liquid or on solid BHI after treatment. However, their transcriptome did not differ from those of bacteria heated at 58°C F=3 (PFDR > 0.01). Transcriptomic data obtained at 71°C were significantly different from the others. The expression of dnaK and groEL was significantly lower at 71°C than at 58°C and 60°C (P < 0.0001). Furthermore, despite similar cell viability and integrity post-treatment, 132 and 8 genes were differentially expressed at 58°C and 60°C F=3, respectively (P-FDR < 0.01) when compared to 71°C. These eight genes, whose expression was upregulated at 71°C, may be considered as good biomarkers to test antimicrobial efficiency of heatstress

Physiological adaptation of Escherichia coli after transfer onto refrigerated ground meat and other solid matrices : a molecular approach

Bacteria on meat are subjected to specific living conditions that differ drastically from typical laboratory procedures in synthetic media. This study was undertaken to determine the behavior of bacteria when transferred from a rich-liquid medium to solid matrices, as is the case during microbial process validation. Escherichia coli cultured in Brain–Heart Infusion (BHI) broth to different growth phases were inoculated in ground beef (GB) and stored at 5 °C for 12 days or spread onto BHI agar and cooked meat medium (CMM), and incubated at 37 °C for several hours. We monitored cell densities and the expression of σ factors and genes under their control over time. The initial growth phase of the inoculum influenced growth resumption after transfer onto BHI agar and CMM. Whatever the solid matrix, bacteria adapted to their new environment and did not perceive stress immediately after inoculation. During this period, the σE and σH regulons were not activated and rpoD mRNA levels adjusted quickly. The rpoS and gadA mRNA levels did not increase after inoculation on solid surfaces and displayed normal growth-dependent modifications. After transfer onto GB, dnaK and groEL gene expression was affected more by the low temperature than by the composition of a meat environment

Infrared supercontinuum generated in concatenated InF3 and As2Se3 fibers

We report on infrared supercontinuum (SC) generation through subsequent nonlinear propagation in concatenated step-index fluoride and As2Se3 fiber. These fibers were pumped by an all-fiber laser source based on an erbium amplifier followed by a thulium power amplifier. ZBLAN and InF3 fibers were compared for the concatenated scheme. The broadest SC produced was achieved by optimizing the length of the InF3 fiber. This arrangement allowed the generation of 200 mW infrared SC with high spectral flatness and spanning from 1.4 μm to 6.4 μm

Search for dark matter produced in association with bottom or top quarks in √s = 13 TeV pp collisions with the ATLAS detector

A search for weakly interacting massive particle dark matter produced in association with bottom or top quarks is presented. Final states containing third-generation quarks and miss- ing transverse momentum are considered. The analysis uses 36.1 fb−1 of proton–proton collision data recorded by the ATLAS experiment at √s = 13 TeV in 2015 and 2016. No significant excess of events above the estimated backgrounds is observed. The results are in- terpreted in the framework of simplified models of spin-0 dark-matter mediators. For colour- neutral spin-0 mediators produced in association with top quarks and decaying into a pair of dark-matter particles, mediator masses below 50 GeV are excluded assuming a dark-matter candidate mass of 1 GeV and unitary couplings. For scalar and pseudoscalar mediators produced in association with bottom quarks, the search sets limits on the production cross- section of 300 times the predicted rate for mediators with masses between 10 and 50 GeV and assuming a dark-matter mass of 1 GeV and unitary coupling. Constraints on colour- charged scalar simplified models are also presented. Assuming a dark-matter particle mass of 35 GeV, mediator particles with mass below 1.1 TeV are excluded for couplings yielding a dark-matter relic density consistent with measurements