Relating Fractal Dimension to Branching Behaviour in Filamentous Microorganisms

Abstract

The productivity of an industrial fermentation process involving a filamentous microbe is heavily dependent on the morphological form adopted by the organism. The development of systems capable of rapidly and accurately characterising morphology within a given process represents a significant challenge to biotechnologists, as the complex phenotypes that are manifested are often not easily quantified. Conventional parameters employed in these analyses are of limited value, as they reveal little about the specific branching behaviour of the organism, which is an important consideration given the demonstrated link between branching frequency and metabolite production. More recently, fractal geometry has been employed in the analysis of microbes, but a clear link between fractal dimension and branching behaviour has not been demonstrated. This study presents an alternative means of enumerating the fractal dimension of fungal mycelial structures, by generating a ‘fractal signal’ from an object boundary. In the analysis of a population of Aspergillus oryzae mycelia, both fractal dimension and hyphal growth unit were found to increase together over time. An extensive analysis of different populations of Penicillium chrysogenum and A. oryzae mycelia, cultivated under a variety of different conditions, revealed a strong correlation between fractal dimension and hyphal growth unit. The technique has the potential to be adapted and applied to any morphological form that may be encountered in a fermentation process, providing a universally applicable process parameter for more complete data acquisition.