Modelling the color development in Biolog microtiter plates by the Gompertz function

The color development curves obtained from multiple readings of Biolog GN m icrotiter plates over a long incubation time were fitted to the Gompertz fu nction. This yielded - for each sole-carbon source the incubation time inde pendent and biologically relevant Gompertz parameters A (maximal extent of color development), mu(M) (specific color development rate) and lambda (lag time). To evaluate the applicability of the model, the coefficients of dete rmination, the residuals, the biological significance of the parameters, th e stability of the parameter estimates and the predicting power of the mode l were determined. For the pure strains Vibrio alginolyticus and Pseudomona s fluorescens the model passed all the criteria. For the model community co nsisting of a mixture of 9 strains, all criteria were met for almost all th e oxidized carbon sources. However, a high amount of measuring points in th e color development curve is necessary (preferably >20) and the reading fre quency needs to be the highest in the lagphase and the exponential phase to ensure a high stability and predictability of the estimates of mu(M) and l ambda, especially when the color develops very rapidly in the wells. For a few carbon sources the Gompertz model was not appropriate, as the color dev elopment curve showed clearly 2 tiers. However, it is substantiated that th e second tier may be eliminated from the time series, which allowed the mod el again to pass all the criteria. Finally, comparison of Biolog fingerprin ts of environmental samples was made with principal component analysis of t he estimated Gompertz parameters for each carbon source. It is shown that t his approach is practicable and may yield consistent results for environmen tal microbial community analysis.