Advances in citric acid fermentation by Aspergillus niger: biochemical aspects, membrane transport and modeling.

Many of the commercial production processes for organic acids are excellent examples of fungal biotechnology. However, unlike penicillin, the organic acids have had a less visible impact on human well-being. Indeed, organic acid fermentations are often not even identified as fungal bioprocesses, having been overshadowed by the successful deployment of the β-lactam processes. Yet, in terms of productivity, fungal organic acid processes may be the best examples of all. For example, commercial processes using Aspergillus niger in aerated stirred-tank-reactors can convert glucose to citric acid with greater than 80% efficiency and at final concentrations in hundreds of grams per liter. Surprisingly, this phenomenal productivity has been the object of relatively few research programs. Perhaps a greater understanding of this extraordinary capacity of filamentous fungi to produce organic acids in high concentrations will allow greater exploitation of these organisms via application of new knowledge in this era of genomics-based biotechnology.

Organic Acid Production by Filamentous Fungi

Citric acid is a commodity chemical produced and consumed throughout The World. It is used mainly in the food and beverage industry, primarily as an acidulant. Although it is one of the oldest industrial fermentations, its World production is still in rapid increasing. Global production of citric acid in 2007 was over 1.6 million tones. Biochemistry of citric acid fermentation, various microbial strains, as well as various substrates, technological processes and product recovery are presented. World production and economics aspects of this strategically product of bulk biotechnology are discussed.

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Citric acid production.

Effect of indigenous Mesorhizobium spp. and plant growth promoting rhizobacteria on yields and nutrients uptake of chickpea (Cicer arietinum L.) under sustainable agriculture

Facility in the targeted manipulation of the genetic and metabolic composition of organisms, combined with unprecedented computational power, is forging a niche for a new subspecialty of biotechnology called metabolic engineering. First published in 2002, this book introduces researchers and advanced students in biology and engineering to methods of optimizing biochemical systems of biotechnological relevance. It examines the development of strategies for manipulating metabolic pathways, demonstrates the need for effective systems models, and discusses their design and analysis, while placing special emphasis on optimization. The authors propose power-law models and methods of biochemical systems theory toward these ends. All concepts are derived from first principles, and the text is richly illustrated with numerous graphs and examples throughout. Special features include: nontechnical and technical introductions to models of biochemical systems; a review of basic methods of model design and analysis; concepts of optimization; and detailed case studies.

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Pathway Analysis and Optimization in Metabolic Engineering

Under the conditions of citric acid fermentation, Aspergillus niger WU-2223L possessed at least two respiratory systems. One system was sensitive to cyanide (CN) and the other was sensitive to salicylhydroxamic acid (SHAM). The respiration of mycelia was partially, inhibited by CN or SHAM, and was completely inhibited in the presence of both CN and SHAM. With culture time, the CN-sensitivity of respiration decreased and the SHAM-sensitivity increased. The respiratory rate itself decreased suddenly at 4 days and thereafter remained at a low level. The SHAM-sensitive respiration was localized in the mitochondria. The alterations of respiration in the mitochondria were similar to those observed in mycelial cells.

Yuji Hirowatari

Papers

Alterations of Respiratory Systems in Aspergillus niger under the Conditions of Citric Acid Fermentation