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Under the Scope
by Dr. Rajiv Sahay
 Aspergillus Terreus Aspergillus species are highly aerobic and are found in almost all oxygen-rich environments, where they commonly grow as molds on the surface of a substrate, as a result of the high oxygen tension. Commonly, fungi are grown on carbon-rich substrates, mainly monosaccharides such as glucose. Aspergilli, however, can also secrete amylase enzymes, which allow it to use polysaccharides as a carbon source, for example starch. As a result of this, Aspergillus species are common contaminants of starchy foods, for example bread and potato, and grow in or on many plants and trees.
In addition to growth on carbon sources such as glucose, fructose, maltose, and starch, many species of Aspergillus demonstrate oligotrophy: they are capable of growing in nutrient-depleted environments, or environments in which there is a complete lack of key nutrients. A. niger is a prime example of this; it can be found growing on damp walls, or as a major component of mildew
Species of Aspergillus are without a doubt an important microorganism, both medically and commercially. Some species can cause human infection, others are important in commercial, microbial fermentations.
In Asian countries, alcoholic beverages such as Japanese sake are made from rice, rather than from grapes, barley or corn. This fermentation is carried out entirely by microorganisms, instead of by plant amylases, or animal amylases (saliva) and yeast. Firstly, koji mold such as Aspergillus oryzae is used to convert the starch in the rice to sugars (saccharification), which are subsequently fermented by other microorganisms, such as yeast (Saccharomyces) and lactic acid bacteria.
Perhaps the most well-known application of A. niger is as the major source of citric acid; this organism accounts for over 99% of global citric acid production, or more than 4.5 million tonnes per annum. A. niger is also commonly used for the production of native and foreign enzymes, including glucose oxidase and hen egg white lysozyme. In these instances, the culture is rarely grown on a solid substrate, although this is still common practice in Japan, but is more often grown as a submerged culture in a bioreactor. In this way, the most important parameters can be strictly controlled, and maximal productivity can be achieved. It also makes it far easier to separate the chemical or enzyme of importance from the medium, and is therefore far more cost-effective
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