| Budget Amount *help |
¥2,500,000 (Direct Cost: ¥2,500,000)
Fiscal Year 1999: ¥600,000 (Direct Cost: ¥600,000)
Fiscal Year 1998: ¥1,900,000 (Direct Cost: ¥1,900,000)
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| Research Abstract |
Filamentous fungi show variety of colony growth patterns depending upon the environmental conditions. In this study, a multi-layer mycelial colony that had three main parameters of nutrient level, nutrient diffusion and hyphal growth rate was constructed. By comparing the model growth with the real fungal colony growth, the selection rules of mycelial colony patterns were investigated.
Without nutrient diffusion, the model colonies exhibited equivalent self-affinity in their roughening of colony fronts at any nutrient levels the colony growth can be maintained. The same result was also obtained for the cases of infinite nutrient limit case. However, the growth exponents of front roughness were found dependent upon the nutrient levels for the multi-layer models. These results showed that the hyphal production in the interior of the colonized space affected the roughening of colony fronts.
The nutrient diffusion brought about the variation of growth patterns. Particularly, as the growth ra
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te was lowered at fixed nutrient levels and nutrient diffusion coefficient, the colony exhibited reaction-limited growth and formed densely aggregated patterns. Under this condition, as the nutrient level was lowered, the ramified morphology was found to develop through reaction-limited process.
By comparing the model colony morphology with the real mycelial colonies, the pattern selection rule was found to exist in the inherent manner of response in the hyphal growth rate to the environmental nutrient levels. The wild and mutant strains of Aspergillus nidulans were grouped into two types; those maintained uniform growth at any nutrient and agar levels, and those exhibited ramified patterns at low nutrient levels. By measuring the colony expansion rates at various nutrient levels, these morphological types can be related with the mutation-induced decay of the growth rate at low nutrient levels.
Further, to consider the effect of growth inhibition by the hyphal aging etc., long-term measurement of hyphal growth rate was commenced for A. nidulans and other strains. Gradual or steep decay of hyphal growth rate was found in the growth process, and it was suggested that the manner of growth rate reduction was dependent upon the environmental nutrient levels. Less
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