Single-Cell Analysis of the Dps Response to Oxidative Stress.

UNLABELLED: Microorganisms have developed an elaborate spectrum of mechanisms to respond and adapt to environmental stress conditions. Among these is the expression of dps, coding for the DNA-binding protein from starved cells. Dps becomes the dominant nucleoid-organizing protein in stationary-phase Escherichia coli cells and is required for robust survival under stress conditions, including carbon or nitrogen starvation, oxidative stress, metal exposure, and irradiation. To study the complex regulation of Dps in E. coli, we utilized time-lapse fluorescence microscopy imaging to examine the kinetics, input encoding, and variability of the Dps response in single cells. In the presence of an oxidative stressor, we observed a single pulse of activation of Dps production. Increased concentrations of H2O2 led to increased intensity and duration of the pulse. While lower concentrations of H2O2 robustly activated the Dps response with little effect on the growth rate, higher concentrations of H2O2 resulted in dramatically lower and highly varied growth rates. A comparison of cells exposed to the same concentration of H2O2 revealed that increased levels of Dps expression did not confer a growth advantage, indicating that recovery from stress may rely primarily upon variation in the amount of damage caused to individual cells. IMPORTANCE: We show for the first time the response of the DNA-binding protein from starved cells (Dps) to oxidative stress in single cells of E. coli Through time-lapse fluorescence microscopy, a single pulse of Dps production is observed in cells exposed to H2O2, with a duration and intensity of induction proportional to the concentration of the applied stress. More intense Dps expression did not provide a growth benefit to the bacteria, suggesting that healing from oxidative stress may largely depend upon the amount of damage in each individual cell.

Room temperature synthesis of perylene diimides facilitated by high amic acid solubility.

A novel protocol for the synthesis of perylene diimides (PDIs), by reacting perylene dianhydride (PDA) with aliphatic amines is reported. Full conversions were obtained at temperatures between 20 and 60 °C, using DBU as the base in DMF or DMSO. A "green" synthesis of PDIs, that runs at higher temperatures, was developed using K2CO3 in DMSO. The reaction sequence for the imidization process, via perylene amic acid intermediates (PAAs), has been confirmed experimentally aided by the synthesis and full characterization of stable model amic acid salts and amic esters. Kinetic studies, using absorption spectroscopy, have established that PDI formation proceeds via fast amic acid formation, followed by a slow conversion to imides. Solubility of the intermediate PAA salts is found to be low and rate-limiting. Based on this finding, quantitative PDI synthesis at room temperature was achieved by diluting the reaction mixture with water, the solvent in which PAA salts have better solubility. Thus, the otherwise harsh synthesis of PDIs has been transformed into an extremely convenient functional group tolerant and highly efficient reaction that runs at room temperature.

Does Transcranial Magnetic Stimulation Have an Added Value to Clinical Assessment in Predicting Upper-Limb Function Very Early After Severe Stroke?

BACKGROUND: The added prognostic value of transcranial magnetic stimulation (TMS)-induced motor-evoked potentials (MEPs) to clinical modeling for the upper limb is still unknown early poststroke. OBJECTIVE: To determine the added prognostic value of TMS of the adductor digiti minimi (TMS-ADM) to the clinical model based on voluntary shoulder abduction (SA) and finger extension (FE) during the first 48 hours and at 11 days after stroke. METHODS: This was a prospective cohort study with 3 logistic regression models, developed to predict upper-limb function at 6 months poststroke. The first model showed the predictive value of SA and FE measured within 48 hours and at 11 days poststroke. The second model included TMS-ADM, whereas the third model combined clinical and TMS-ADM information. Differences between derived models were tested with receiver operating characteristic curve analyses. RESULTS: A total of 51 patients with severe, first-ever ischemic stroke were included. Within 48 hours, no significant added value of TMS-ADM to clinical modeling was found ( P = .369). Both models suffered from a relatively low negative predictive value within 48 hours poststroke. TMS-ADM combined with SA and FE (SAFE) showed significantly more accuracy than TMS-ADM alone at 11 days poststroke ( P = .039). CONCLUSION: TMS-ADM showed no added value to clinical modeling when measured within first 48 hours poststroke, whereas optimal prediction is achieved by SAFE combined with TMS-ADM at 11 days poststroke. Our findings suggest that accuracy of predicting upper-limb motor function by TMS-ADM is mainly determined by the time of assessment early after stroke onset.