A COMPARISON OF METHODS FOR DETERMINING THE FRACTAL DIMENSIONS OF COLONIES OF FILAMENTOUS BACTERIA

Several techniques for measuring fractal geometry were applied to grow ing colonies of three nocardioform actinomycetes with different colony morphologies or space filling properties to assess their suitability for quantitative characterization of colony morphology. Fractal dimens ion (D) increased with size and complexity of colonies of the filament ous Nocardia asteroides and Nocardia otitidiscaviarum, but decreased s lightly with the non-filamentous Rhodococcus erythropolis. Box count m ethods were superior to calipers methods for analysing colonies, but i t was necessary to use software which allowed multiple determinations at different starting points on the colony outline to increase measure ment accuracy. Problems were encountered in obtaining straight lines i n some Richardson plots with data from the calipers method used for ca lculating D, but we were unable to interpret our data according to a s emi fractal model suggested by others. Although the fractal dimension obtained from the area-perimeter relation showed potential as a descri ptor of colony shape, data from a larger number of colonies are requir ed to confirm this. In our study, the mass-radius method was only usef ul for the largest colony of N. asteroides. Possible applications of f ractal analysis in microbial colony characterisation are discussed.