Journal of Bioscience and Bioengineering Vol. 102, No. 5  (Novermber 2006)  Cover

Localization of alternative oxidase in mitochondoria of citric acid-producing Aspergillus niger.

A filamentous fungus Aspergillus niger is industrially used for the production of citric acid. However, it remains unclear why citric acid is overproduced by A. niger. The cyanide-insensitive respiratory pathway, catalyzed by an alternative oxidase (AOX) has been shown to contribute to the production of a large amount of the acid. As the first step to analyze the mechanism underlying the overproduction of citric acid, a fusion gene, aox1-egfp, encoding AOX and enhanced green fluorescent protein (EGFP) were constructed and introduced into A. niger.

In A. niger transformant, the fusion protein AOX-EGFP was confirmed to occur in mitochondria through the comparison of the sites of the green fluorescence by AOX-EGFP (middle panel) with those of the red fluorescence stained with Mito Tracker Red CMXRos (bottom panel), suggesting the relation between citric acid production and AOX in A. niger.

Related article: Kirimura, K., Ogawa, S., Hattori, T., and Kino, K., "Expression analysis of alternative oxidase gene (aox1) with enhanced green fluorescent protein as marker in citric acid-producing Aspergillus niger", J. Biosci. Bioeng., vol. 102, 210-214 (2006).