Dieter Helm

Elaboration of a procedure for identification of bacteria using Fourier-Transform IR spectral libraries: a stepwise correlation approach

Abstract Bacteria display typical, fingerprint-like IR spectra, which are specific for different species and strains. On this basis, we have developed a computer-aided, fast-working procedure suitable for the identification of bacteria. Spectra were recorded within the range from 4000 to 500 cm −1 and were mathematically filtered to enhance spectral resolution. 97 different strains, comprising Gram-negative and Gram-positive bacteria, were used to create a spectrum test library. 72 of these strains were randomly selected, repetitively measured and used as ‘unknowns’ which were challenged against the spectra library. Quantitative comparison was performed on the basis of spectral dissimilarity. Dissimilarity between spectra was calculated as a suitably transformed and normalized Pearsons product moment correlation coefficient. Consideration of the entire spectrum yielded a relatively poor quota of correct matches of 43.1% at the species level and 31.9% at the strain level. However, subdivision of the entire spectrum into a number of distinct and nonredundant subranges enabled a stepwise comparison of the ‘unknowns’ with the test library. This more sophisticated advance, providing a remarkable data reduction at the same time, yielded an overall quota of correct matches of 94.4% at the species level and 83.3% at the strain level with most of the misidentified strains belonging to the Gram-negative bacteria.

Characterization and Identification of Micro-Organisms by FT-IR Spectroscopy and FT-IR Microscopy

A large series of physical techniques has been tested for the characterization of microbial cells. These techniques include gas chromatographic (GC) and high-performance liquid chromatographic (HPLC) techniques, gel electrophoresis, pyrolysis mass spectroscopy, fluorescence and chemiluminescence techniques, flow cytometry, impedance measurements, microcalorimetry, circular intensity differential scattering, nuclear magnetic resonance, and infrared as well as Raman spectroscopy (for review see Nelson, 1991). All these efforts have provided additional biochemical and structural information, which might -in some areas -be helpful for taxonomic characterizations.

Climate policy: The Kyoto approach has failed

Abandon coal, price carbon consumption and look to new technologies for a lasting solution to global emissions, argues Dieter Helm.

Evaluation of Biomonitoring Data

The construction of posets or Hasse diagrams is a profitable means for the evaluation of biomonitoring data. In contrast to other statistical approaches the Hasse Diagram Technique enables the consideration of multiple attributes at the same time and will result in at least partially ordered data sets. Moreover, the calculation of averaged ranks allows the construction of a total order for a given data set. For the evaluation of biomonitoring data, as obtained for the German Environmental Specimen Bank, the Hasse diagram technique was applied to achieve partially or totally ordered data. The following scheme was applied: i) Careful rounding of the original data to increase the number of comparabilities; ii) splitting of the data in smaller sub-sets; iii) construction of the posets for each sub-set; iv) construction of the total order for each sub-set (by means of averaged ranks) and, v) synopsis of the sub-sets.

Trendanalysen mit Mann-Kendall-Test und Theil-Schätzer@@@Weighting of data in trend analysis: Teil 2: Gewichtung der Daten

ZusammenfassungZiel und AbsichtEs wird eine Erweiterung für Trendanalysen mit dem Mann-Kendall-Test und der linearen Regression nach Theil vorgestellt, die eine Gewichtung der zu analysierenden Daten ermöglicht.MethodenAn Hand eines erdachten Beispiels wird die Auswirkung der Gewichtung auf die Ergebnisse des Mann-Kendall-Tests und der Regression nach Theil demonstriert. Die Gewichtungsfaktoren leiten sich dabei von den Stichprobenumfängen ab, auf die sich aggregierte Daten oder Mischproben gründen. Ein Wert, der die Information von mehr Individuen repräsentiert, soll stärkere Beachtung finden als ein Wert, der auf weniger Individuen zurückgeht.Ergebnisse und SchlussfolgerungenDie Erweiterung wirkt sich auf die Ergebnisse der Theil-Regression aus. Unter Gewichtung neigt sich die Ausgleichsgerade stärker den Datenpunkten mit größeren Stichproben zu.AusblickDie Umsetzung der vorgeschlagenen Erweiterungen zur Trendanalyse mit dem Mann-Kendall-Test und der Regression nach Theil (Berücksichtigung von Messunsicherheiten und Gewichtung der Daten) steht in der Praxis noch aus.AbstractGoal and ScopeAn extension for trend analysis with Mann Kendall test and Theil estimator is presented which enables the weighting of data by weight factors.MethodsIt is shown in which way the weighting can effect the outcome of a trend analysis. Weighting is done in relation to the different sample sizes of the data points. A value or an observation derived from many specimens will be considered more reliable than a value derived from only a few specimens and will thus get a higher weighting factor.ResultsWhen weighting is applied, this will effect the Theil estimator rather than the Mann Kendall test. As a result the regression line is tilted towards those points with higher weights.OutlookFuture must show whether the extensions presented here and in part 1 prove to be practical for the trend analysis in environmental monitoring or not.