YtfK activates the stringent response by triggering the alarmone synthetase SpoT in Escherichia coli

The stringent response is a general bacterial stress response that allows bacteria to adapt and survive adverse conditions. This reprogramming of cell physiology is caused by the accumulation of the alarmone (p)ppGpp which, in Escherichia coli, depends on the (p)ppGpp synthetase RelA and the bifunctional (p)ppGpp synthetase/hydrolase SpoT. Although conditions that control SpoT-dependent (p)ppGpp accumulation have been described, the molecular mechanisms regulating the switching from (p)ppGpp degradation to synthesis remain poorly understood. Here, we show that the protein YtfK promotes SpoT-dependent accumulation of (p)ppGpp in E. coli and is required for activation of the stringent response during phosphate and fatty acid starvation. Our results indicate that YtfK can interact with SpoT. We propose that YtfK activates the stringent response by tilting the catalytic balance of SpoT toward (p)ppGpp synthesis.

POLAR MODELLING AND SEGMENTATION OF GENOMIC MICROARRAY SPOTS USING MATHEMATICAL MORPHOLOGY

Robust image analysis of spots in microarrays (quality control + spot segmentation + quantification) is a requirement for automated software which is of fundamental importance for a high-throughput analysis of genomics microarray-based data. This paper deals with the development of model-based image processing algorithms for qualifying/segmenting/quantifying adaptively each spot according to its morphology. A series of morphologicalmodels for spot intensities are introduced. The spot typologies representmost of the possible qualitative cases identified from a large database (different routines, techniques, etc.). Then, based on these spot models, a classification framework has been developed. The spot feature extraction and classification (without segmenting) is based on converting the spot image to polar coordinates and, after computing the radial/angular projections, the calculation of granulometric curves and derived parameters from these projections. Spot contour segmentation can also be solved by working in polar coordinates, calculating the up/downminimal path, which is easily obtained with the generalized distance function. With this model-based technique, the segmentation can be regularised by controlling different elements of the algorithm. According to the spot typology (e.g., doughnut-like or egg-like spots), several minimal paths can be computed to obtain a multi-region segmentation. Moreover, this segmentation is more robust and sensible to weak spots, improving the previous approaches.

Detection of sulfamethazine in water, milk and pig manure by dipstick immunoassay

During the past few years, there has been an increasing interest in rapid visual tests that could be performed outside the laboratory, for example on farms, in store houses or in food production plants. Hence, cost effective and simple screening methods are required for residual analysis of environmental and food samples on-site. Here, a simple and instrumental independent dipstick immunoassay for sulfamethazine detection is described. The polyclonal antibody was optimised in terms of coating dilution on a nitrocellulose membrane, dilution of peroxidase tracer conjugate, blocking agents and incubation times. Test results assessed by visual measurement can be available within 20 minutes. In buffer, water, skimmed milk and pig manure extract, sulfamethazine fortified at 50 and 100 µg/l has exhibited clear visual differentiation in colour development (lower intensity) in comparison to the control spot intensity (high intensity) of the dipstick.

Laboratory assessment of three new monitors of blood glucose: Accu-Chek II, Glucometer II, and Glucoscan 2000.

We describe a laboratory assessment of three new monitors of blood glucose concentrations: the Boehringer "Accu-Chek II" (B), the Ames "Glucometer II" (A), and the Lifescan "Glucoscan 2000" (L). Inherent imprecision (CV) of each monitor was less than 2%. Maximum difference between individual monitors of the same type was less than or equal to 0.5 mmol/L. The volume of blood applied to the test strips is not critical, but duration of blood incubation or color development should be precise. Two types of test strips retained sufficient color 48 h after development to allow checking of the original measurement, and would be suitable as quality-control "spot" checks. Correlation coefficients for results for whole-blood glucose vs those for serum glucose (measured with the Beckman ASTRA-8) were: 0.992 (B), 0.967 (A), and 0.988 (L). Bias plots of these data showed positive bias for A (0.45 mmol/L) and L (0.17 mmol/L) in relation to serum-glucose measurements, but a negative bias of 0.32 mmol/L for B. Calibration solutions are not interchangeable. Although these versions of the monitors are probably not analytically superior to earlier models, they are easier to use.