Abstract
BackgroundAspergillus niger is a highly important industrial microorganism because of its amazing capacity to produce citric acid (CA). To explore the metabolic mechanism and physiological phenotype associated with high CA productivity, the transcriptomes of high CA-producing A. niger YX-1217 and degenerative strain YX-1217G were investigated using A. niger ATCC1015 as a control.ResultsThese strains showed distinct transcriptional differences in CA production. By contrast, the genes encoding glycoside hydrolases, aspartyl endoproteases, and carboxypeptidases were unusually upregulated in CA-producing strain YX-1217, which involved the carbohydrate hydrolysis and polypeptide degradation pathways, and should be related to its powerful capacity to utilize cornmeal fluidified liquid as raw material for the production of CA. In central metabolism of YX-1217, gene 9.735.1, which encodes glyceraldehyde 3-phosphate dehydrogenase, and two transcriptionally outstanding genes, 6000119 (An15g01920) and 3.2152.1 (An08g10920) that encode citrate synthase, were upregulated, thereby ensuring CA accumulation. In addition, a relatively strong electron transport chain, a regeneration system for NAD+/NADP+, and an efficient resistance mechanism may have contributed to the high CA production rate of YX-1217.ConclusionsThese comparisons have shed light on the mechanism underlying high CA yield in A. niger YX-1217 as well as provide insights into the development of novel strains that produce other organic acids.
Highlights
Aspergillus niger is a highly important industrial microorganism because of its amazing capacity to produce citric acid (CA)
The central metabolism among the three strains displayed no substantial differences, while the better central metabolism was an important premise for strain YX-1217 to overproduce CA
In strain YX-1217, abundant synaptic vesicles could accelerate the absorption and utilization of materials such as sugar that were prepared for the production of CA
Summary
Aspergillus niger is a highly important industrial microorganism because of its amazing capacity to produce citric acid (CA). Aspergillus niger is a ubiquitous fungus with powerful metabolic capabilities for the hydrolysis of carbohydrates and the production of organic acids and proteins. It has been widely used as an industrial workhorse to commercially produce organic acids such as citric acid (CA) and gluconic acid, as well as industrial proteins such as enzymes and active proteins (Krijgsheld et al 2013; Andersen et al 2008). As a powerful industrial enzyme producer, the genome of A. niger CBS513.88 was sequenced and analyzed by DSM Food Specialties in 2007 (Pel et al 2007).
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