Inoculum-size phenomena in Aspergillus oryzae

McIntosh, A. F (1966) Inoculum-size phenomena in Aspergillus oryzae. PhD thesis, University of Glasgow.

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Reports by a number of authors in widely differing fields of biological study have shown that various phenomena accompany a change in the size of an inoculum. Such phenomena have been shown in the present work to occur in cultures of Aspergillus oryzae under a variety of conditions. The importance of size of inoculum in growth, in metabolism of carbon and nitrogen and in respiration has been considered. The size of the inoculum chosen has been found to be a determinating factor in each one of the aspects of metabolism studied. It has been shown in growth experiments, particularly with reference to maximum yield that deep cultures are influenced by inoculum size to a greater extent than are stationary cultures and that increase in mechanical stress enhances the effect of inoculum size. Large-inoculum cultures usually show a higher maximum yield than do small-inoculum cultures. The effects of inoculum size on growth are generally more pronounced when no trace elements are added. The effect of trace elements has been examined not only by using trace-element-poor chemicals, but by blocking trace elements with a chelating agent, removing them by a purification procedure or adding them individually or in combination. It has been shown that each individual trace element mates its own contribution to the inoculum size effect and the resultant effect is a composite one depending upon the balance of trace elements in the substrate. A balance can be struck which can give a reversal of the usual effects of inoculum size, that is, smaller growth rate or maximum yield are obtained with large-inoculum cultures. Caramelization of the substrate results in a masking of the effects. Aspergillus oryzae has been shown to produce substances inhibitory and stimulatory to its own growth. stimulating substances are evident in large-inoculum cultures at all stages of growth and in small-inoculum cultures at late stages of growth. Inhibitory substances predominate in early stages of growth of small-inoculum cultures. Since the differences between results for the growth experiments were sometimes small, statistical methods were applied to assess the validity of claims made. The metabolism of carbon and nitrogen has been studied in this work. Consideration of the utilization of the carbon source and production of acids, together with incorporation and excretion of nitrogen has shown that large-inoculum cultures are generally more efficient than small-inoculum cultures at comparable mycelium contents, as the mycelium ages, it decreases in efficiency. A number of factors influence the respiratory; activity of Aspergillus oryzae. At late stages of growth, uptake of oxygen is reduced. Uptake of oxygen is reduced when the mycelium ages, or is subjected to a washing treatment, or is collected on a detergent-treated filter. Each individual component of the substrate has some influence on rate of uptake of oxygen. Small-inoculum cultures at all stages of growth capable of being collected and examined had the low rate of uptake found in late (but not in early) stages of growth of large-inoculum cultures.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Additional Information: Adviser: E O Morris
Keywords: Plant sciences
Date of Award: 1966
Depositing User: Enlighten Team
Unique ID: glathesis:1966-72791
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 11 Jun 2019 11:06
Last Modified: 11 Jun 2019 11:06

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