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UBC Theses and Dissertations

A study of the trace element nutrition of Aspergillus niger, in relation to the production of citric acid Tomlinson, Neil


The literature regarding the fungus Aspergillus niger contains proof of the essential nature of the trace elements zinc, iron, copper, and manganese for the growth of this organism. Workers who have investigated the process for the production of citric acid utilizing A. niger have, for the most part, either ignored the influence of these elements on the process, or have relied on their presence as chance contaminants of other components of the fermentation media. A few reports have been presented indicating that zinc and iron are necessary for maximum acid production, but copper and manganese usually have been found to be without effect or to be harmful. However, two investigators interested in the growth of the organism, rather than in acid production, have suggested that copper, in addition to zinc and iron, is necessary for acid production. These suggestions were based on pH changes observed in media on which the organism was growing. In addition to the four trace elements mentioned above, unconfirmed reports have been published indicating that gallium, scandium, and vanadium may play a role in the nutrition of the fungus. No evidence for the need of any other trace element for growth of A. niger has been presented. The present study was conducted for the purpose of investigating the influence of these trace elements on the production of citric acid by the fermentation process. The strain of A. niger used was one known to be capable of producing high yields of citric acid from cane sugar. The experimental work resulted in the demonstration of the need for zinc, iron, manganese, and copper for citric acid production. It was also found that the quantities of these elements made available to the fungus must be less than the amounts needed for good growth of the organism. However, evidence has been found which indicates these four trace elements alone are not sufficient and that possibly one or more others are required. When a basal medium of the following composition was used: [formula omitted]. The trace element additions enabling highest production of citric acid were: [formula omitted]. The yield obtained under these conditions was only about 83% of that obtained when untreated sucrose was the carbon source. The table following shows the per cent loss in acid production if the addition to the basal medium of any one or all of the four trace elements is omitted: [table omitted].

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