The morphology of filamentous fungi.

The morphology of fungi has received attention from both pure and applied scientists. The subject is complicated, because many genes and physiological mechanisms are involved in the development of a particular morphological type: its morphogenesis. The contribution from pure physiologists is growing steadily as more and more details of the transport processes and the kinetics involved in the morphogenesis become known. A short survey of these results is presented. Various mathematical models have been developed for the morphogenesis as such, but also for the direct relation between morphology and productivity--as production takes place only in a specific morphological type. The physiological basis for a number of these models varies from thorough to rather questionable. In some models, assumptions have been made that are in conflict with existing physiological know-how. Whether or not this is a problem depends on the purpose of the model and on its use for extrapolation. Parameter evaluation is another aspect that comes into play here. The genetics behind morphogenesis is not yet very well developed, but needs to be given full attention because present models and practices are based almost entirely on the influence of environmental factors on morphology. This makes morphogenesis rather difficult to control, because environmental factors vary considerably during production as well as on scale. Genetically controlled morphogenesis might solve this problem. Apart from a direct relation between morphology and productivity, there is an indirect relation between them, via the influence of morphology on transport phenomena in the bioreactor. The best way to study this relation is with viscosity as a separate contributing factor.